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Nuclear calcium (Ca2+) signaling is crucial for symbiotic interactions between legumes and beneficial microbes, such as rhizobia and arbuscular mycorrhizal fungi. The ion channels DMI1 and CNGC15 are key to generating repetitive nuclear Ca2+ oscillations. Despite more than 20 years of research on symbiotic nuclear Ca2+ spiking, important questions remain, including the exact function of the DMI1 channel. This review highlights recent developments that have filled knowledge gaps regarding the regulation of CNGC15 and its interplay with DMI1. We also explore new insights into the evolutionary conservation of DMI1-induced symbiotic nuclear Ca2+ oscillations and the roles of CNGC15 and DMI1 beyond symbiosis, such as in nitrate signaling, and discuss new questions this raises. As we delve deeper into the regulatory mechanisms and evolutionary history of these ion channels, we move closer to fully understanding the roles of nuclear Ca2+ signaling in plant life. [ABSTRACT FROM AUTHOR]

Raffinose mitigates plant heat, drought, and cold stresses; however, whether raffinose contributes to plant waterlogging tolerance is unknown. The maize raffinose synthase mutant zmrafs-1 had seedlings that lack raffinose, generated fewer and shorter adventitious roots, and were more sensitive to waterlogging stress, while overexpression of the raffinose synthase gene, ZmRAFS , increased raffinose content, stimulated adventitious root formation, and enhanced waterlogging tolerance of maize seedlings. Transcriptome analysis of null segregant seedlings compared with zmrafs-1 , particularly when waterlogged, revealed that the expression of genes related to galactose metabolism and the auxin biosynthetic pathway were up-regulated by raffinose. Additionally, indole-3-acetic acid content was significantly decreased in zmrafs-1 seedlings and increased in ZmRAFS -overexpressing seedlings. Inhibition of the hydrolysis of raffinose by 1-deoxygalactonojirimycin decreased the waterlogging tolerance of maize seedlings, the expression of genes encoding proteins related to auxin transport-related genes, and the indole-3-acetic acid level in the seedlings, indicating that the hydrolysis of raffinose is necessary for maize waterlogging tolerance. These data demonstrate that raffinose catabolism stimulates adventitious root formation via the auxin signaling pathway to enhance maize waterlogging tolerance. [ABSTRACT FROM AUTHOR]

The triple response phenotype is characteristic for seedlings treated with the phytohormone ethylene or its direct precursor 1-aminocyclopropane-carboxylic acid, and is often employed to find novel chemical tools to probe ethylene responses. We identified a benzoxazole-urea derivative (B2) partially mimicking ethylene effects in a triple response bioassay. A phenotypic analysis demonstrated that B2 and its closest analogue arinole (ARI) induced phenotypic responses reminiscent of seedlings with elevated levels of auxin, including impaired hook development and inhibition of seedling growth. Specifically, ARI reduced longitudinal cell elongation in roots, while promoting cell division. In contrast to other natural or synthetic auxins, ARI mostly acts as an inducer of adventitious root development, with only limited effects on lateral root development. Quantification of free auxins and auxin biosynthetic precursors as well as auxin-related gene expression demonstrated that ARI boosts global auxin levels. In addition, analyses of auxin reporter lines and mutants, together with pharmacological assays with auxin-related inhibitors, confirmed that ARI effects are facilitated by TRYPTOPHAN AMINOTRANSFERASE1 (TAA1)-mediated auxin synthesis. ARI treatment in an array of species, including Arabidopsis, pea, tomato, poplar, and lavender, resulted in adventitious root formation, which is a desirable trait in both agriculture and horticulture. [ABSTRACT FROM AUTHOR]

This article explores the development of adventitious roots in rose cuttings and the factors that contribute to successful root formation. The study uses imaging and spectroscopy techniques to investigate the differences between easy-to-root and hard-to-root rose cultivars. The researchers find that cell wall composition plays a crucial role in the emergence of adventitious roots. The findings highlight the importance of integrated approaches to overcome propagation challenges. The article suggests that a better understanding of the physiology of rooting recalcitrance could lead to more effective propagation strategies. [Extracted from the article]

Reactive oxygen species (ROS) are essential signaling molecules that enable cells to respond rapidly to a range of stimuli. The ability of plants to recognize various stressors, incorporate a variety of environmental inputs, and initiate stress-response networks depends on ROS. Plants develop resilience and defensive systems as a result of these processes. Root hairs are central components of root biology since they increase the surface area of the root, anchor it in the soil, increase its ability to absorb water and nutrients, and foster interactions between microorganisms. In this review, we specifically focused on root hair cells and we highlighted the identification of ROS receptors, important new regulatory hubs that connect ROS production, transport, and signaling in the context of two hormonal pathways (auxin and ethylene) and under low temperature environmental input related to nutrients. As ROS play a crucial role in regulating cell elongation rates, root hairs are rapidly gaining traction as a very valuable single plant cell model for investigating ROS homeostasis and signaling. These promising findings might soon facilitate the development of plants and roots that are more resilient to environmental stressors. [ABSTRACT FROM AUTHOR]

The rhizotoxicity of protons (H+) in acidic soils is a fundamental constraint that results in serious yield losses. However, the mechanisms underlying H+-mediated inhibition of root growth are poorly understood. In this study, we revealed that H+-induced root growth inhibition in Arabidopsis depends considerably on excessive iron deposition in the root apoplast. Reducing such aberrant iron deposition by decreasing the iron supply or disrupting the ferroxidases LOW PHOSPHATE ROOT 1 (LPR) and LPR2 attenuates the inhibitory effect of H+ on primary root growth efficiently. Further analysis showed that excessive iron deposition triggers a burst of highly reactive oxygen species, consequently impairing normal root development. Our study uncovered a valuable strategy for improving the ability of plants to tolerate H+ toxicity by manipulating iron availability. [ABSTRACT FROM AUTHOR]

Plants have an incredible ability to sustain root and vascular growth after initiation of the embryonic root and the specification of vascular tissue in early embryos. Microarray assays have revealed that a group of transcription factors, TARGET OF MONOPTEROS (TMO), are important for embryonic root initiation in Arabidopsis. Despite the discovery of their auxin responsiveness early on, their function and mode of action remained unknown for many years. The advent of genome editing has accelerated the study of TMO transcription factors, revealing novel functions for biological processes such as vascular development, root system architecture, and response to environmental cues. This review covers recent achievements in understanding the developmental function and the genetic mode of action of TMO transcription factors in Arabidopsis and other plant species. We highlight the transcriptional and post-transcriptional regulation of TMO transcription factors in relation to their function, mainly in Arabidopsis. Finally, we provide suggestions for further research and potential applications in plant genetic engineering. [ABSTRACT FROM AUTHOR]

The toxicity of aluminum (Al) in acidic soil inhibits plant root development and reduces crop yields. In the plant response to Al toxicity, the initiation of programmed cell death (PCD) appears to be an important mechanism for the elimination of Al-damaged cells to ensure plant survival. In a previous study, the type I metacaspase AhMC1 was found to regulate the Al stress response and to be essential for Al-induced PCD. However, the mechanism by which AhMC1 is altered in the peanut response to Al stress remained unclear. Here, we show that a nuclear protein, mutator-like transposable element 9A (AhMULE9A), directly interacts with AhMC1 in vitro and in vivo. This interaction occurs in the nucleus in peanut and is weakened during Al stress. Furthermore, a conserved C2HC zinc finger domain of AhMULE9A (residues 735–751) was shown to be required for its interaction with AhMC1. Overexpression of AhMULE9A in Arabidopsis and peanut strongly inhibited root growth with a loss of root cell viability under Al treatment. Conversely, knock down of AhMULE9A in peanut significantly reduced Al uptake and Al inhibition of root growth, and alleviated the occurrence of typical hallmarks of Al-induced PCD. These findings provide novel insight into the regulation of Al-induced PCD. [ABSTRACT FROM AUTHOR]

Plant roots fulfil crucial tasks during a plant's life. As roots encounter very diverse conditions while exploring the soil for resources, their growth and development must be responsive to changes in the rhizosphere, resulting in root architectures that are tailor-made for all prevailing circumstances. Using multi-disciplinary approaches, we are gaining more intricate insights into the regulatory mechanisms directing root system architecture. This Special Issue provides insights into our advancement of knowledge on different aspects of root development and identifies opportunities for future research. [ABSTRACT FROM AUTHOR]

A growing understanding is emerging of the roles of peptide hormones in local and long-distance signalling that coordinates plant growth and development as well as responses to the environment. C-TERMINALLY ENCODED PEPTIDE (CEP) signalling triggered by its interaction with CEP RECEPTOR 1 (CEPR1) is known to play roles in systemic nitrogen (N) demand signalling, legume nodulation, and root system architecture. Recent research provides further insight into how CEP signalling operates, which involves diverse downstream targets and interactions with other hormone pathways. Additionally, there is emerging evidence of CEP signalling playing roles in N allocation, root responses to carbon levels, the uptake of other soil nutrients such as phosphorus and sulfur, root responses to arbuscular mycorrhizal fungi, plant immunity, and reproductive development. These findings suggest that CEP signalling more broadly coordinates growth across the whole plant in response to diverse environmental cues. Moreover, CEP signalling and function appear to be conserved in angiosperms. We review recent advances in CEP biology with a focus on soil nutrient uptake, root system architecture and organogenesis, and roles in plant–microbe interactions. Furthermore, we address knowledge gaps and future directions in this research field. [ABSTRACT FROM AUTHOR]

Plant submergence is a major abiotic stress that impairs plant performance. Under water, reduced gas diffusion exposes submerged plant cells to an environment that is enriched in gaseous ethylene and is limited in oxygen (O2) availability (hypoxia). The capacity for plant roots to avoid and/or sustain critical hypoxia damage is essential for plants to survive waterlogging. Plants use spatiotemporal ethylene and O2 dynamics as instrumental flooding signals to modulate potential adaptive root growth and hypoxia stress acclimation responses. However, how non-adapted plant species modulate root growth behaviour during actual waterlogged conditions to overcome flooding stress has hardly been investigated. Here we discuss how changes in the root growth rate, lateral root formation, density, and growth angle of non-flood adapted plant species (mainly Arabidopsis) could contribute to avoiding and enduring critical hypoxic conditions. In addition, we discuss current molecular understanding of how ethylene and hypoxia signalling control these adaptive root growth responses. We propose that future research would benefit from less artificial experimental designs to better understand how plant roots respond to and survive waterlogging. This acquired knowledge would be instrumental to guide targeted breeding of flood-tolerant crops with more resilient root systems. [ABSTRACT FROM AUTHOR]

Every living organism on Earth depends on its interactions with other organisms. In the rhizosphere, plants and microorganisms constantly exchange signals and influence each other's behavior. Recent studies have shown that many beneficial rhizosphere microbes can produce specific signaling molecules that affect plant root architecture and therefore could have substantial effects on above-ground growth. This review examines these chemical signals and summarizes their mechanisms of action, with the aim of enhancing our understanding of plant–microbe interactions and providing references for the comprehensive development and utilization of these active components in agricultural production. In addition, we highlight future research directions and challenges, such as searching for microbial signals to induce primary root development. [ABSTRACT FROM AUTHOR]

Lateral roots are a major component of root system architecture, and lateral root count (LRC) positively contributes to yield under drought in chickpea. To understand the genetic regulation of LRC, a biparental mapping population derived from two chickpea accessions having contrasting LRCs was genotyped by sequencing, and phenotyped to map four major quantitative trait loci (QTLs) contributing to 13–32% of the LRC trait variation. A single- nucleotide polymorphism tightly linked to the locus contributing to highest trait variation was located on the coding region of a gene (CaWIP2), orthologous to NO TRANSMITTING TRACT/WIP domain protein 2 (NTT/WIP2) gene of Arabidopsis thaliana. A polymorphic simple sequence repeat (SSR) in the CaWIP2 promoter showed differentiation between low versus high LRC parents and mapping individuals, suggesting its utility for marker-assisted selection. CaWIP2 promoter showed strong expression in chickpea apical root meristem and lateral root primordia. Expression of CaWIP2 under its native promoter in the Arabidopsis wip2wip4wip5 mutant rescued its rootless phenotype to produce more lateral roots than the wild-type plants, and led to formation of amyloplasts in the columella. CaWIP2 expression also induced the expression of genes that regulate lateral root emergence. Our study identified a gene-based marker for LRC which will be useful for developing drought-tolerant, high-yielding chickpea varieties. [ABSTRACT FROM AUTHOR]

Linker of nucleoskeleton and cytoskeleton (LINC) complexes consist of outer nuclear membrane KASH proteins, interacting in the nuclear envelope lumen with inner nuclear membrane SUN proteins and connecting the nucleus and cytoskeleton. The paralogous Arabidopsis KASH proteins SINE1 and SINE2 function during stomatal dynamics induced by light–dark transitions and abscisic acid (ABA), which requires F-actin reorganization. SINE2 influences actin depolymerization and SINE1 actin repolymerization. The actin-related protein 2/3 (ARP2/3) complex, an actin nucleator, and the plant actin-bundling and -stabilizing factor SCAB1 are involved in stomatal aperture control. Here, we have tested the genetic interaction of SINE1 and SINE2 with SCAB1 and the ARP2/3 complex. We show that SINE1 and the ARP2/3 complex function in the same pathway during ABA-induced stomatal closure, while SINE2 and the ARP2/3 complex play opposing roles. The actin repolymerization defect observed in sine1-1 is partially rescued in scab1-2 sine1-1 , while SINE2 is epistatic to SCAB1. In addition, SINE1 and ARP2/3 act synergistically in lateral root development. The absence of SINE2 renders trichome development independent of the ARP2/3 complex. Together, these data reveal complex and differential interactions of the two KASH proteins with the actin-remodeling apparatus and add evidence to the proposed differential role of SINE1 and SINE2 in actin dynamics. [ABSTRACT FROM AUTHOR]

Phytohormones play a central role in plant development and environmental responses. Auxin is a classical hormone that is required for organ formation, tissue patterning, and defense responses. Auxin pathways have been extensively studied across numerous land plant lineages, including bryophytes and eudicots. In contrast, our understanding of the roles of auxin in maize morphogenesis and immune responses is limited. Here, we review evidence for auxin-mediated processes in maize and describe promising areas for future research in the auxin field. Several recent transcriptomic and genetic studies have demonstrated that auxin is a key influencer of both vegetative and reproductive development in maize (namely roots, leaves, and kernels). Auxin signaling has been implicated in both maize shoot architecture and immune responses through genetic and molecular analyses of the conserved co-repressor RAMOSA ENHANCER LOCUS2. Polar auxin transport is linked to maize drought responses, root growth, shoot formation, and leaf morphogenesis. Notably, maize has been a key system for delineating auxin biosynthetic pathways and offers many opportunities for future investigations on auxin metabolism. In addition, crosstalk between auxin and other phytohormones has been uncovered through gene expression studies and is important for leaf and root development in maize. Collectively these studies point to auxin as a cornerstone for maize biology that could be leveraged for improved crop resilience and yield. [ABSTRACT FROM AUTHOR]

Robust agricultural yields require consistent flower production throughout fluctuating environmental conditions. Floral primordia are produced in the inflorescence meristem, which contains a pool of continuously dividing stem cells. Daughter cells of these divisions either retain stem cell identity or are pushed to the SAM periphery, where they become competent to develop into floral primordia after receiving the appropriate signal. Thus, flower production is inherently linked to regulation of the stem cell pool. The plant hormone auxin promotes flower development throughout its early phases and has been shown to interact with the molecular pathways regulating stem cell maintenance. Here, we will summarize how auxin signaling contributes to stem cell maintenance and promotes flower development through the early phases of initiation, outgrowth, and floral fate establishment. Recent advances in this area suggest that auxin may serve as a signal that integrates stem cell maintenance and new flower production. [ABSTRACT FROM AUTHOR]

S -Nitrosoglutathione plays a central role in nitric oxide (NO) homeostasis, and S -nitrosoglutathione reductase (GSNOR) regulates the cellular levels of S -nitrosoglutathione across kingdoms. Here, we investigated the role of endogenous NO in shaping shoot architecture and controlling fruit set and growth in tomato (Solanum lycopersicum). SlGSNOR silencing promoted shoot side branching and led to reduced fruit size, negatively impacting fruit yield. Greatly intensified in slgsnor knockout plants, these phenotypical changes were virtually unaffected by SlGSNOR overexpression. Silencing or knocking out of SlGSNOR intensified protein tyrosine nitration and S -nitrosation and led to aberrant auxin production and signaling in leaf primordia and fruit-setting ovaries, besides restricting the shoot basipetal polar auxin transport stream. SlGSNOR deficiency triggered extensive transcriptional reprogramming at early fruit development, reducing pericarp cell proliferation due to restrictions on auxin, gibberellin, and cytokinin production and signaling. Abnormal chloroplast development and carbon metabolism were also detected in early-developing NO-overaccumulating fruits, possibly limiting energy supply and building blocks for fruit growth. These findings provide new insights into the mechanisms by which endogenous NO fine-tunes the delicate hormonal network controlling shoot architecture, fruit set, and post-anthesis fruit development, emphasizing the relevance of NO–auxin interaction for plant development and productivity. [ABSTRACT FROM AUTHOR]

Plant root growth and developmental capacities reside in a few stem cells of the root apical meristem (RAM). Maintenance of these stem cells requires regenerative divisions of the initial stem cell niche (SCN) cells, self-maintenance, and proliferative divisions of the daughter cells. This ensures sufficient cell diversity to guarantee the development of complex root tissues in the plant. Damage in the root during growth involves the formation of a new post-embryonic root, a process known as regeneration. Post-embryonic root development and organogenesis processes include primary root development and SCN maintenance, plant regeneration, and the development of adventitious and lateral roots. These developmental processes require a fine-tuned balance between cell proliferation and maintenance. An important regulator during root development and regeneration is the gasotransmitter nitric oxide (NO). In this review we have sought to compile how NO regulates cell rate proliferation, cell differentiation, and quiescence of SCNs, usually through interaction with phytohormones, or other molecular mechanisms involved in cellular redox homeostasis. NO exerts a role on molecular components of the auxin and cytokinin signaling pathways in primary roots that affects cell proliferation and maintenance of the RAM. During root regeneration, a peak of auxin and cytokinin triggers specific molecular programs. Moreover, NO participates in adventitious root formation through its interaction with players of the brassinosteroid and cytokinin signaling cascade. Lately, NO has been implicated in root regeneration under hypoxia conditions by regulating stem cell specification through phytoglobins. [ABSTRACT FROM AUTHOR]

In nature, plant shoots are exposed to light whereas the roots grow in relative darkness. Surprisingly, many root studies rely on in vitro systems that leave the roots exposed to light whilst ignoring the possible effects of this light on root development. Here, we investigated how direct root illumination affects root growth and development in Arabidopsis and tomato. Our results show that in light-grown Arabidopsis roots, activation of local phytochrome A and B by far-red or red light inhibits respectively PHYTOCHROME INTERACTING FACTORS 1 or 4, resulting in decreased YUCCA4 and YUCCA6 expression. As a result, auxin levels in the root apex become suboptimal, ultimately resulting in reduced growth of light-grown roots. These findings highlight once more the importance of using in vitro systems where roots are grown in darkness for studies that focus on root system architecture. Moreover, we show that the response and components of this mechanism are conserved in tomato roots, thus indicating its importance for horticulture as well. Our findings open up new research possibilities to investigate the importance of light-induced root growth inhibition for plant development, possibly by exploring putative correlations with responses to other abiotic signals, such as temperature, gravity, touch, or salt stress. [ABSTRACT FROM AUTHOR]

As auxin is a major regulator of plant development, studying the signaling mechanisms by which auxin influences cellular activities is of primary importance. In this review, we describe current knowledge on the different modalities of signaling, from the well-characterized canonical nuclear auxin pathway, to the more recently discovered or re-discovered non-canonical modes of auxin signaling. In particular, we discuss how both the modularity of the nuclear auxin pathway and the dynamic regulation of its core components allow specific transcriptomic responses to be triggered. We highlight the fact that the diversity of modes of auxin signaling allows for a wide range of time scales of auxin responses, from second-scale cytoplasmic responses to minute-/hour-scale modifications of gene expression. Finally, we question the extent to which the temporality of auxin signaling and responses contributes to development in both the shoot and the root meristems. We conclude by stressing the fact that future investigations should allow an integrative view to be built not only of the spatial control, but also of the temporality of auxin-mediated regulation of plant development, from the cell to the whole organism. [ABSTRACT FROM AUTHOR]

Lateral root initiation requires the accumulation of auxin in lateral root founder cells, yielding a local auxin maximum. The positioning of auxin maxima along the primary root determines the density and spacing of lateral roots. The GOLVEN6 (GLV6) and GLV10 signaling peptides and their receptors have been established as regulators of lateral root spacing via their inhibitory effect on lateral root initiation in Arabidopsis. However, it was unclear how these GLV peptides interfere with auxin signaling or homeostasis. Here, we show that GLV6/10 signaling regulates the expression of a subset of auxin response genes, downstream of the canonical auxin signaling pathway, while simultaneously inhibiting the establishment of auxin maxima within xylem-pole pericycle cells that neighbor lateral root initiation sites. We present genetic evidence that this inhibitory effect relies on the activity of the PIN3 and PIN7 auxin export proteins. Furthermore, GLV6/10 peptide signaling was found to enhance PIN7 abundance in the plasma membranes of xylem-pole pericycle cells, which likely stimulates auxin efflux from these cells. Based on these findings, we propose a model in which the GLV6/10 signaling pathway serves as a negative feedback mechanism that contributes to the robust patterning of auxin maxima along the primary root. [ABSTRACT FROM AUTHOR]

When interacting with the environment, plant roots integrate sensory information over space and time in order to respond appropriately under non-uniform conditions. The complexity and dynamic properties of soil across spatial and temporal scales pose a significant technical challenge for research into the mechanisms that drive metabolism, growth, and development in roots, as well as on inter-organismal networks in the rhizosphere. Synthetic environments, combining microscopic access and manipulation capabilities with soil-like heterogeneity, are needed to elucidate the intriguing antagonism that characterizes subsurface ecosystems. Microdevices have provided opportunities for innovative approaches to observe, analyse, and manipulate plant roots and advanced our understanding of their development, physiology, and interactions with the environment. Initially conceived as perfusion platforms for root cultivation under hydroponic conditions, microdevice design has, in recent years, increasingly shifted to better reflect the complex growth conditions in soil. Heterogeneous micro-environments have been created through co-cultivation with microbes, laminar flow-based local stimulation, and physical obstacles and constraints. As such, structured microdevices provide an experimental entry point into the complex network behaviour of soil communities. [ABSTRACT FROM AUTHOR]

Root hairs are single-celled tubular structures produced from the epidermis, which play an essential role in water and nutrient uptake from the soil. Therefore, root hair formation and elongation are controlled not only by developmental programs but also by environmental factors, enabling plants to survive under fluctuating conditions. Phytohormones are key signals that link environmental cues to developmental programs; indeed, root hair elongation is known to be controlled by auxin and ethylene. Another phytohormone, cytokinin, also affects root hair growth, while whether cytokinin is actively involved in root hair growth and, if so, how it regulates the signaling pathway governing root hair development have remained unknown. In this study, we show that the two-component system of cytokinin, which involves the B-type response regulators ARABIDOPSIS RESPONSE REGULATOR 1 (ARR1) and ARR12, promotes the elongation process of root hairs. They directly up-regulate ROOT HAIR DEFECTIVE 6-LIKE 4 (RSL4) encoding a basic helix–loop–helix (bHLH) transcription factor that plays a central role in root hair growth, whereas the ARR1/12–RSL4 pathway does not crosstalk with auxin or ethylene signaling. These results indicate that cytokinin signaling constitutes another input onto the regulatory module governed by RSL4, making it possible to fine-tune root hair growth in changing environments. [ABSTRACT FROM AUTHOR]

The root cap is a small tissue located at the tip of the root with critical functions for root growth. Present in nearly all vascular plants, the root cap protects the root meristem, influences soil penetration, and perceives and transmits environmental signals that are critical for root branching patterns. To perform these functions, the root cap must remain relatively stable in size and must integrate endogenous developmental pathways with environmental signals, yet the mechanism is not clear. We previously showed that low pH conditions altered root cap development, and these changes are mediated by the NIN LIKE PROTEIN 7 (NLP7) transcription factor, a master regulator of nitrate signaling. Here we show that in Arabidopsis NLP7 integrates nitrate signaling with auxin pathways to regulate root cap development. We found that low nitrate conditions promote aberrant release of root cap cells. Nitrate deficiency impacts auxin pathways in the last layer of the root cap, and this is mediated in part by NLP7. Mutations in NLP7 abolish the auxin minimum in the last layer of the root cap and alter root cap expression of the auxin carriers PIN-LIKES 3 (PILS3) and PIN-FORMED 7 (PIN7) as well as transcription factors that regulate PIN expression. Together, our data reveal NLP7 as a link between endogenous auxin pathways and nitrate signaling in the root cap. [ABSTRACT FROM AUTHOR]

Calcium release to the nucleoplasm of root meristem cells was demonstrated to modulate root development. The calcium channel encoded by cyclic nucleotide-gated channel (CNGC) 15 localizes at the nuclear envelope in young Arabidopsis seedlings. In contrast, at later stages of root growth, overexpression analysis showed that AtCNGC15 can relocalize to the plasma membrane to mediate primary nitrate-induced gene expression. This raises the question as to whether nuclear localized AtCNGC15 is required for root apical meristem development in young Arabidopsis seedlings, and whether nitrate signalling occurs independently of nuclear localized AtCNGC15 at this developmental stage. In this study, we characterize a novel mutant allele of AtCNGC15 and demonstrate that the mutation of a highly conserved aspartic acid in the C-linker domain is sufficient to impair the gating of AtCNCG15. We demonstrate that AtCNGC15 mediates the nuclear calcium release that modulates root apical meristem development and nitrate-induced LBD39 expression. We also show that, in the presence of nitrate, the relocalization of AtCNGC15 at the plasma membrane occurs specifically in the columella cells. Our results further suggest that the induction of LBD37 , LBD38 , and LBD39 in the presence of nitrate is modulated by different inputs of cytoplasmic or nuclear calcium release. [ABSTRACT FROM AUTHOR]

Transcriptional networks are crucial to integrate various internal and external signals into optimal responses during plant growth and development. In Arabidopsis thaliana , primary root vasculature patterning and proliferation are controlled by a network centred around the basic Helix-Loop-Helix transcription factor complex, formed by TARGET OF MONOPTEROS 5 (TMO5) and LONESOME HIGHWAY (LHW), which control cell proliferation and division orientation by modulating the cytokinin response and other downstream factors. Despite recent progress, many aspects of the TMO5/LHW pathway are not fully understood. In particular, the upstream regulators of TMO5/LHW activity remain unknown. Here, using a forward genetics approach to identify new factors of the TMO5/LHW pathway, we discovered a novel function of the MYB-type transcription factor, MYB12. MYB12 physically interacts with TMO5 and dampens the TMO5/LHW-mediated induction of direct target gene expression, as well as the periclinal/radial cell divisions. The expression of MYB12 is activated by the cytokinin response, downstream of TMO5/LHW, resulting in a novel MYB12-mediated negative feedback loop that restricts TMO5/LHW activity, to ensure optimal cell proliferation rates during root vascular development. [ABSTRACT FROM AUTHOR]

ROOT MERISTEM GROWTH FACTOR1 (RGF1) and its receptors RGF1 INSENSITIVEs (RGIs) regulate primary root meristem activity via a mitogen-activated protein kinase (MPK) signaling cascade in Arabidopsis. However, it is unknown how RGF1 regulates lateral root (LR) development. Here, we show that the RGF1–RGI1 peptide–receptor pair negatively regulates LR development via activation of PUCHI encoding AP2/EREBP. Exogenous RGF1 peptides inhibited LR development of the wild type. However, the rgi1 mutants were partially or fully insensitive to RGF1 during LR development, whereas four other rgi single mutants, namely rgi2 , rgi3 , rgi4 , and rgi5 , were sensitive to RGF1 in inhibiting LR formation. Consistent with this, the red fluorescent protein (RFP) signals driven by the RGF1 promoter were detected at stage I and the following stages, overlapping with RGI1 expression. PUCHI expression was significantly up-regulated by RGF1 but completely inhibited in rgi1. LR development of puchi1-1 was insensitive to RGF1. PUCHI expression driven by the RGI1 promoter reduced LR density in both the wild type and rgi1,2,3. Further, mpk6 , but not mpk3 , displayed significantly down-regulated PUCHI expression and insensitive LR development in response to RGF1. Collectively, these results suggest that the RGF1–RGI1 module negatively regulates LR development by activating PUCHI expression via MPK6. [ABSTRACT FROM AUTHOR]

The phytohormone jasmonate is an essential endogenous signal in the regulation of multiple plant processes for environmental adaptation, such as primary root growth inhibition and root hair elongation. Perception of environmental stresses promotes the accumulation of jasmonate, which is sensed by the CORONATINE INSENSITIVE1 (COI1)–JASMONATE ZIM-DOMAIN (JAZ) co-receptor, triggering the degradation of JAZ repressors and induction of transcriptional reprogramming. The basic helix–loop–helix (bHLH) subgroup IIIe transcription factors MYC2, MYC3, and MYC4 are the most extensively characterized JAZ-binding factors and together stimulate jasmonate-signaled primary root growth inhibition. Conversely, the bHLH subgroup IIId transcription factors (i.e. bHLH3 and bHLH17) physically associate with JAZ proteins and suppress jasmonate-induced root growth inhibition. For root hair development, JAZ proteins interact with and inhibit ROOT HAIR DEFECTIVE 6 (RHD6) and RHD6 LIKE1 (RSL1) transcription factors to modulate jasmonate-enhanced root hair elongation. Moreover, jasmonate also interacts with other signaling pathways (such as ethylene and auxin) to regulate primary root growth and/or root hair elongation. Here, we review recent progress into jasmonate-mediated primary root growth and root hair development. [ABSTRACT FROM AUTHOR]

Locoweeds are leguminous forbs known for their toxicity to livestock caused by the endophytic fungi Alternaria sect. Undifilum. Unlike the defensive mutualisms reported in many toxin-producing endophytes and their plant hosts, the benefits that A. sect. Undifilum can confer to it host plants remains unclear. Here, we conducted physiological and genetic analyses to show that A. (sect. Undifilum) oxytropis influences growth, especially root development, in its locoweed host Oxytropis ochrocephala and Arabidopsis. The presence of A. oxytropis significantly decreased primary root length while increasing the numbers of lateral roots and root hairs, and increasing plant leaf area and fresh weight. The fungus also increased the concentrations of plant endogenous auxin, and the expression of key genes for auxin biosynthesis, signaling, and transport. These effects on root development were abolished in mutants deficient in auxin signaling and polar transport. Alternaria oxytropis down-regulated expression of PIN1 but increased expression of PIN2 , PIN7 , and AUX1 , which might reflect alterations in the spatial accumulation of auxin responsible for the changes in root architecture. Plant growth was insensitive to A. oxytropis when naphthylphthalamic acid was applied. Our findings indicate a function of A. oxytropis in promoting the growth and development of Arabidopsis via the regulation of auxin, which in turn suggests a possible role in benefiting its locoweed hosts via a process independent of its toxin production. [ABSTRACT FROM AUTHOR]

Medicago truncatula NODULE ROOT1 (MtNOOT1) and Pisum sativum COCHLEATA1 (PsCOCH1) are orthologous genes belonging to the NOOT-BOP-COCH-LIKE (NBCL) gene family which encodes key transcriptional co-regulators of plant development. In Mtnoot1 and Pscoch1 mutants, the development of stipules, flowers, and symbiotic nodules is altered. MtNOOT2 and PsCOCH2 represent the single paralogues of MtNOOT1 and PsCOCH1 , respectively. In M. truncatula , MtNOOT1 and MtNOOT2 are both required for the establishment and maintenance of symbiotic nodule identity. In legumes, the role of NBCL2 in above-ground development is not known. To better understand the roles of NBCL genes in legumes, we used M. truncatula and P. sativum nbcl mutants, isolated a knockout mutant for the PsCOCH2 locus and generated Pscoch1coch2 double mutants in P. sativum. Our work shows that single Mtnoot2 and Pscoch2 mutants develop wild-type stipules, flowers, and symbiotic nodules. However, the number of flowers was increased and the pods and seeds were smaller compared to the wild type. Furthermore, in comparison to the corresponding nbcl1 single mutants, both the M. truncatula and P. sativum nbcl double mutants show a drastic alteration in stipule, inflorescence, flower, and nodule development. Remarkably, in both M. truncatula and P. sativum nbcl double mutants, stipules are transformed into a range of aberrant leaf-like structures. [ABSTRACT FROM AUTHOR]

In eukaryotes, histone acetylation levels directly regulate downstream gene expression. As a plant-specific histone deacetylase (HDAC), HD2D is involved in plant development and abiotic stress. However, the response of HD2D to drought stress and its interacting proteins, is still unclear. In this study, we analysed HD2D gene expression patterns in Arabidopsis, revealing that HD2D gene was highly expressed in roots and rosette leaves, but poorly expressed in other tissues such as stems, flowers, and young siliques. The HD2D gene expression was induced by d -mannitol. We investigated the responses to drought stress in the wild-type plant, HD2D overexpression lines, and hd2d mutants. HD2D- overexpressing lines showed abscisic acid (ABA) hypersensitivity and drought tolerance, and these phenotypes were not present in hd2d mutants. RNA-seq analysis revealed the transcriptome changes caused by HD2D under drought stress, and showed that HD2D responded to drought stress via the ABA signalling pathway. In addition, we demonstrated that CASEIN KINASE II (CKA4) directly interacted with HD2D. The phosphorylation of Ser residues on HD2D by CKA4 enhanced HD2D enzymatic activity. Furthermore, the phosphorylation of HD2D was shown to contribute to lateral root development and ABA sensing in Arabidopsis, but, these phenotypes could not be reproduced by the overexpression of Ser-phospho-null HD2D lines. Collectively, this study suggests that HD2D responded to drought stress by regulating the ABA signalling pathway, and the expression of drought stress-related genes. The regulatory mechanism of HD2D mediated by CKII phosphorylation provides new insights into the ABA response and lateral root development in Arabidopsis. [ABSTRACT FROM AUTHOR]

Adventitious root (AR) development is an extremely complex biological process that is affected by many intrinsic factors and extrinsic stimuli. Some WUSCHEL-related homeobox (WOX) transcription factors have been reported to play important roles in AR development, but their functional relationships with auxin signaling are poorly understood, especially the developmental plasticity of roots in response to adversity stress. Here, we identified that the WOX11/12a– SMALL AUXIN UP RNA36 (SAUR36) module mediates AR development through the auxin pathway in poplar, as well as under salt stress. PagWOX11/12a displayed inducible expression during AR development, and overexpression of PagWOX11/12a significantly promoted AR development and increased salt tolerance in poplar, whereas dominant repression of PagWOX11/12a produced the opposite phenotype. PagWOX11/12a proteins directly bind to the SAUR36 promoter to regulate SAUR36 transcription, and this binding was enhanced during salt stress. Genetic modification of PagWOX11/12a–PagSAUR36 expression revealed that the PagWOX11/12a –PagSAUR36 module is crucial for controlling AR development via the auxin pathway. Overall, our results indicate that a novel WOX11 –SAUR –auxin signaling regulatory module is required for AR development in poplar. These findings provide key insights and a better understanding of the involvement of WOX11 in root developmental plasticity in saline environments. [ABSTRACT FROM AUTHOR]

Wheat is one of the world's major staple food crops, and breeding for improvement of grain yield is a priority under the scenarios of climate change and population growth. WRKY transcription factors are multifaceted regulators in plant growth, development, and responses to environmental stimuli. In this study, we identify the WRKY gene TaGSNE (Grain Size and Number Enhancer) in common wheat, and find that it has relatively high expression in leaves and roots, and is induced by multiple abiotic stresses. Eleven single-nucleotide polymorphisms were identified in TaGSNE , forming two haplotypes in multiple germplasm collections, named as TaGSNE-Hap-1 and TaGSNE-Hap-2. In a range of different environments, TaGSNE-Hap-2 was significantly associated with increases in thousand-grain weight (TGW; 3.0%) and spikelet number per spike (4.1%), as well as with deeper roots (10.1%) and increased root dry weight (8.3%) at the mid-grain-filling stage, and these were confirmed in backcross introgression populations. Furthermore, transgenic rice lines overexpressing TaGSNE had larger panicles, more grains, increased grain size, and increased grain yield relative to the wild-type control. Analysis of geographic and temporal distributions revealed that TaGSNE-Hap-2 is positively selected in China and Pakistan, and TaGSNE-Hap-1 in Europe. Our findings demonstrate that TaGSNE overcomes the trade-off between TGW/grain size and grain number, leading us to conclude that these elite haplotypes and their functional markers could be utilized in marker-assisted selection for breeding high-yielding varieties. [ABSTRACT FROM AUTHOR]

Although the division of the pericycle cells initiates both lateral root development and root-derived callus formation, these developmental processes are affected differently in the strigolactone and karrikin/KARRIKIN INSENSITIVE 2 (KAI2) ligand signalling mutant more axillary growth 2 (max2). Whereas max2 produces more lateral roots than the wild type, it is defective in the regeneration of shoots from root explants. We suggest that the decreased shoot regeneration of max2 originates from delayed formation of callus primordium, yielding less callus material to regenerate shoots. Indeed, when incubated on callus-inducing medium, the pericycle cell division was reduced in max2 and the early gene expression varied when compared with the wild type, as determined by a transcriptomics analysis. Furthermore, the expression of the LATERAL ORGAN BOUNDARIES DOMAIN genes and of callus-induction genes was modified in correlation with the max2 phenotype, suggesting a role for MAX2 in the regulation of the interplay between cytokinin, auxin, and light signalling in callus initiation. Additionally, we found that the in vitro shoot regeneration phenotype of max2 might be caused by a defect in KAI2, rather than in DWARF14, signalling. Nevertheless, the shoot regeneration assays revealed that the strigolactone biosynthesis mutants max3 and max4 also play a minor role. [ABSTRACT FROM AUTHOR]

The meristem is the most functionally dynamic part in a plant. The shaping of the meristem requires constant cell division and elongation, which are influenced by hormones and the cytoskeletal component, actin. Although the roles of hormones in modulating meristem development have been extensively studied, the role of actin in this process is still elusive. Using the single and double mutants of the vegetative class actin, we demonstrate that actin isovariant ACT7 plays an important role in root meristem development. In the absence of ACT7, but not ACT8 and ACT2, depolymerization of actin was observed. Consistently, the act7 mutant showed reduced cell division, cell elongation, and meristem length. Intracellular distribution and trafficking of auxin transport proteins in the actin mutants revealed that ACT7 specifically functions in the root meristem to facilitate the trafficking of auxin efflux carriers PIN1 and PIN2, and consequently the transport of auxin. Compared with act7 , the act7act8 double mutant exhibited slightly enhanced phenotypic response and altered intracellular trafficking. The altered distribution of auxin in act7 and act7act8 affects the response of the roots to ethylene, but not to cytokinin. Collectively, our results suggest that ACT7-dependent auxin-ethylene response plays a key role in controlling Arabidopsis root meristem development. [ABSTRACT FROM AUTHOR]

Small secreted peptides have been described as key contributors to complex signalling networks that control plant development and stress responses. The Brassicaceae-specific PROSCOOP family encodes precursors of Serine riCh endOgenOus Peptides (SCOOPs). In Arabidopsis SCOOP12 has been shown to promote the defence response against pathogens and to be involved in root development. Here, we explore its role as a moderator of Arabidopsis primary root development. We show that the PROSCOOP12 null mutation leads to longer primary roots through the development of longer differentiated cells while PROSCOOP12 overexpression induces dramatic plant growth impairments. In comparison, the exogenous application of synthetic SCOOP12 peptide shortens roots through meristem size and cell length reductions. Moreover, superoxide anion (O2·−) and hydrogen peroxide (H2O2) production in root tips vary according to SCOOP12 abundance. By using reactive oxygen species scavengers that suppress the proscoop12 phenotype, we showed that root growth regulation by SCOOP12 is associated with reactive oxygen species metabolism. Furthermore, our results suggest that peroxidases act as potential SCOOP12 downstream targets to regulate H2O2 production, which in turn triggers cell wall modifications in root. Finally, a massive transcriptional reprogramming, including the induction of genes from numerous other pathways, including ethylene, salicylic acid, and glucosinolates biosynthesis, was observed, emphasizing its dual role in defence and development. [ABSTRACT FROM AUTHOR]

The balance between cell growth, proliferation and differentiation emerges from gene regulatory networks coupled to various signal transduction pathways, including reactive oxygen species (ROS) and transcription factors (TFs), enabling developmental responses to environmental cues. The Arabidopsis thaliana's primary root has become a valuable system for unraveling such networks. Recently, the role of TFs that mediate the ROS's inhibition of primary root growth has begun to be characterized. This study demonstrates that the MADS-box transcription factor XAANTAL1 (XAL1) is an essential regulator of hydrogen peroxide (H2O2) in primary root growth and root stem cell niche identity. Interestingly, our findings suggest that XAL1 acts as a positive regulator of H2O2 concentration in the root meristem by directly regulating genes involved in oxidative stress response, such as PEROXIDASE 28 (PER28). Moreover, we found that XAL1 is necessary for the H2O2-induced inhibition of primary root growth through the negative regulation of peroxidase and catalase activities. Furthermore, XAL1, in conjunction with RETINOBLASTOMA-RELATED (RBR), is essential for positively regulating the differentiation of columella stem cells and for participating in primary root growth inhibition in response to oxidative stress induced by H2O2 treatment., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

4-Cl-IAA, and not IAA, stimulates pericarp GA biosynthesis and pericarp growth ([18]), and the expression of ethylene biosynthesis and signalling genes and ethylene response was differentially modified by the two auxins ([6]; [5]). Keywords: Auxin biosynthesis; auxin receptor; 4-chloro-indole-3-acetic acid; ethylene; gibberellin; pea reproductive development; Pisum sativum EN Auxin biosynthesis auxin receptor 4-chloro-indole-3-acetic acid ethylene gibberellin pea reproductive development Pisum sativum 3831 3835 5 06/28/22 20220624 NES 220624 The growth hormone auxin has been implicated as a necessary factor in the development of different types of fruit. Auxins and gibberellins are decreased in deseeded pods, while the addition of auxin can rescue the pericarp growth phenotype, and 4-Cl gives a better response than IAA. The auxins IAA and 4-Cl-IAA differentially modify gibberellin action via ethylene response in developing pea fruit. [Extracted from the article]

Nitrate is an important nutrient and a key signalling molecule for plant development. A number of transcription factors involved in the response to nitrate and their regulatory mechanisms have been identified. However, little is known about the transcription factors involved in nitrate sensing and their regulatory mechanisms among crop plants. In this study, we identified functions of a nitrate-responsive miR444:MADS-box transcription factor OsMADS27 module and its downstream targets mediating rice root growth and stress responses. Transgenic rice plants expressing miR444 target mimic improved rice root growth. Although miR444 has the potential to target multiple genes, we identified OsMADS27 as the major miR444 target that regulates the expression of nitrate transporters, as well as several key genes including expansins, and those associated with auxin signalling, to promote root growth. In agreement with this, overexpression of miRNA-resistant OsMADS27 improved root development and tolerance to abiotic stresses, while its silencing suppressed root growth. OsMADS27 mediated robust stress tolerance in plants through its ability to bind to the promoters of specific stress regulators, as observed in ChIP-seq analysis. Our results provide evidence of a nitrate-dependent miR444-OsMADS27 signalling cascade involved in the regulation of rice root growth, as well as its surprising role in stress responses. [ABSTRACT FROM AUTHOR]

Lateral root organogenesis is a key process in the development of a plant's root system and its adaptation to the environment. During lateral root formation, an early phase of cell proliferation first produces a four-cell-layered primordium, and only from this stage onwards is a root meristem-like structure, expressing root stem cell niche marker genes, being established in the developing organ. Previous studies reported that the gene regulatory network controlling lateral root formation is organized into two subnetworks whose mutual inhibition may contribute to organ patterning. PUCHI encodes an AP2/ERF transcription factor expressed early during lateral root primordium development and required for correct lateral root formation. To dissect the molecular events occurring during this early phase, we generated time-series transcriptomic datasets profiling lateral root development in puchi-1 mutants and wild types. Transcriptomic and reporter analyses revealed that meristem-related genes were expressed ectopically at early stages of lateral root formation in puchi-1 mutants. We conclude that, consistent with the inhibition of genetic modules contributing to lateral root development, PUCHI represses ectopic establishment of meristematic cell identities at early stages of organ development. These findings shed light on gene network properties that orchestrate correct timing and patterning during lateral root formation. [ABSTRACT FROM AUTHOR]

Plant growth promoting rhizobacteria (PGPR) refer to bacteria that colonize the rhizosphere and contribute to plant growth or stress tolerance. To further understand the molecular mechanism by which PGPR exhibit symbiosis with plants, we performed a high-throughput single colony screening from the rhizosphere, and uncovered a bacterium (named promoting lateral root, PLR) that significantly promotes Arabidopsis lateral root formation. By 16S rDNA sequencing, PLR was identified as a novel sub-species of Serratia marcescens. RNA-seq analysis of Arabidopsis integrated with phenotypic verification of auxin signalling mutants demonstrated that the promoting effect of PLR on lateral root formation is dependent on auxin signalling. Furthermore, PLR enhanced tryptophan-dependent indole-3-acetic acid (IAA) synthesis by inducing multiple auxin biosynthesis genes in Arabidopsis. Genome-wide sequencing of PLR integrated with the identification of IAA and its precursors in PLR exudates showed that tryptophan treatment significantly enhanced the ability of PLR to produce IAA and its precursors. Interestingly, PLR induced the expression of multiple nutrient (N, P, K, S) transporter genes in Arabidopsis in an auxin-independent manner. This study provides evidence of how PLR enhances plant growth through fine-tuning auxin biosynthesis and signalling in Arabidopsis, implying a potential application of PLR in crop yield improvement through accelerating root development. [ABSTRACT FROM AUTHOR]

Crown roots (CRs) are major components of the rice root system. They form at the basal node of the shoot, and their development is greatly influenced by environmental factors. Ammonium nitrogen is known to impact plant root development through ammonium transporters (AMTs), but it remains unclear whether ammonium and AMTs play roles in rice CR formation. In this study, we revealed a significant role of ammonium, rather than nitrate, in regulating rice CR development. High ammonium supply increases CR formation but inhibits CR elongation. Genetic evidence showed that ammonium regulation of CR development relies on ammonium uptake mediated jointly by ammonium transporters OsAMT1;1, OsAMT1;2; OsAMT1;3, and OsAMT2;1, but not on root acidification which was the result of ammonium uptake. OsAMTs are also needed for glutamine-induced CR formation. Furthermore, we showed that polar auxin transport dependent on the PIN auxin efflux carriers acts downstream of ammonium uptake and assimilation to activate local auxin signaling at CR primordia, in turn promoting CR formation. Taken together, our results highlight a critical role for OsAMTs in cooperatively regulating CR formation through regulating auxin transport under nitrogen-rich conditions. [ABSTRACT FROM AUTHOR]

An optimal size of post-embryonic root apical meristem (RAM) is achieved by a balance between cell division and differentiation. Despite extensive research, molecular mechanisms underlying the coordination of cell division and differentiation are still fragmentary. Here, we report that ORESARA 15 (ORE15), an Arabidopsis PLANT A/T-RICH SEQUENCE-AND ZINC-BINDING PROTEIN (PLATZ) transcription factor preferentially expressed in the RAM, determines RAM size. Primary root length, RAM size, cell division rate, and stem cell niche activity were reduced in an ore15 loss-of-function mutant but enhanced in an activation-tagged line overexpressing ORE15 , compared with wild type. ORE15 forms mutually positive and negative feedback loops with auxin and cytokinin signalling, respectively. Collectively, our findings imply that ORE15 controls RAM size by mediating the antagonistic interaction between auxin and cytokinin signalling-related pathways. [ABSTRACT FROM AUTHOR]

Much of what we know about the role of auxin in plant development derives from exogenous manipulations of auxin distribution and signaling, using inhibitors, auxins, and auxin analogs. In this context, synthetic auxin analogs, such as 1-naphthalene acetic acid (1-NAA), are often favored over the endogenous auxin, indole-3-acetic acid (IAA), in part due to their higher stability. While such auxin analogs have proven instrumental in revealing the various faces of auxin, they display in some cases bioactivities distinct from IAA. Here, we focused on the effect of auxin analogs on the accumulation of PIN proteins in brefeldin A-sensitive endosomal aggregations (BFA bodies), and correlation with the ability to elicit Ca2+ responses. For a set of commonly used auxin analogs, we evaluated if auxin analog-induced Ca2+ signaling inhibits PIN accumulation. Not all auxin analogs elicited a Ca2+ response, and their differential ability to elicit Ca2+ responses correlated partially with their ability to inhibit BFA-body formation. However, in tir1/afb and cngc14 , 1-NAA-induced Ca2+ signaling was strongly impaired, yet 1-NAA still could inhibit PIN accumulation in BFA bodies. This demonstrates that TIR1/AFB–CNGC14-dependent Ca2+ signaling does not inhibit BFA body formation in Arabidopsis roots. [ABSTRACT FROM AUTHOR]

C4 photosynthesis increases the efficiency of carbon fixation by spatially separating high concentrations of molecular oxygen from Rubisco. The specialized leaf anatomy required for this separation evolved independently many times. The morphology of C4 root systems is also distinctive and adapted to support high rates of photosynthesis; however, little is known about the molecular mechanisms that have driven the evolution of C4 root system architecture. Using a mutant screen in the C4 model plant Setaria italica , we identify Siaux1-1 and Siaux1-2 as root system architecture mutants. Unlike in S. viridis , AUX1 promotes lateral root development in S. italica. A cell by cell analysis of the Siaux1-1 root apical meristem revealed changes in the distribution of cell volumes in all cell layers and a dependence of the frequency of protophloem and protoxylem strands on SiAUX1. We explore the molecular basis of the role of SiAUX1 in seedling development using an RNAseq analysis of wild-type and Siaux1-1 plants and present novel targets for SiAUX1 -dependent gene regulation. Using a selection sweep and haplotype analysis of SiAUX1 , we show that Hap-2412TT in the promoter region of SiAUX1 is an allele which is associated with lateral root number and has been strongly selected for during Setaria domestication. [ABSTRACT FROM AUTHOR]

The metals iron, zinc, manganese, copper, molybdenum, and nickel are essential for the growth and development of virtually all plant species. Although these elements are required at relatively low amounts, natural factors and anthropogenic activities can significantly affect their availability in soils, inducing deficiencies or toxicities in plants. Because essential trace metals can shape root systems and interfere with the uptake and signaling mechanisms of other nutrients, the non-optimal availability of any of them can induce multi-element changes in plants. Interference by one essential trace metal with the acquisition of another metal or a non-metal nutrient can occur prior to or during root uptake. Essential trace metals can also indirectly impact the plant's ability to capture soil nutrients by targeting distinct root developmental programs and hormone-related processes, consequently inducing largely metal-specific changes in root systems. The presence of metal binding domains in many regulatory proteins also enables essential trace metals to coordinate nutrient uptake by acting at high levels in hierarchical signaling cascades. Here, we summarize the known molecular and cellular mechanisms underlying trace metal-dependent modulation of nutrient acquisition and root development, and highlight the importance of considering multi-element interactions to breed crops better adapted to non-optimal trace metal availabilities. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) plays important roles in plant development. Adventitious roots (AR), lateral buds (LB) and callus formation are important traits for plants. Here, a gene encoding RESPIRATORY BURST OXIDASE HOMOLOG B (PdeRBOHB) from poplar line 'NL895' (Populus. deltoides × P. euramericana) was predicted to be involved in H2O2 accumulation, and lines with reduced expression were generated. H2O2 content was decreased, and the development of adventitious roots, lateral buds, and callus was inhibited in reduced expression PdeRBOHB lines. A gene encoding PdeWRKY75 was identified as the upstream transcription factor positively regulating PdeRBOHB. This regulation was confirmed by dual luciferase reporter assay, GUS transient expression analysis and electrophoretic mobility shift assay. In the reduced expression PdeWRKY75 lines, H2O2 content was decreased and the development of adventitious roots, lateral buds, and callus development was inhibited, while in the overexpression lines, H2O2 content was increased and the development of adventitious roots and lateral buds was inhibited, but callus formation was enhanced. Additionally, reduced expression PdeRBOHB lines showed lowered expression of PdeWRKY75 , while exogenous application of H2O2 showed the opposite effect. Together, these results suggest that PdeWRKY75 and PdeRBOHB are part of a regulatory module in H2O2 accumulation, which is involved in the regulation of multiple biological processes. [ABSTRACT FROM AUTHOR]

The response of plant growth and development to nutrient and water availability is an important adaptation for abiotic stress tolerance. Roots need to intercept both passing nutrients and water while foraging into new soil layers for further resources. Substantial amounts of nitrate can be lost in the field when leaching into groundwater, yet very little is known about how deep rooting affects this process. Here, we phenotyped root system traits and deep 15N nitrate capture across 1.5 m vertical profiles of solid media using tall mesocosms in switchgrass (Panicum virgatum L.), a promising cellulosic bioenergy feedstock. Root and shoot biomass traits, photosynthesis and respiration measures, and nutrient uptake and accumulation traits were quantified in response to a water and nitrate stress factorial experiment for switchgrass upland (VS16) and lowland (AP13) ecotypes. The two switchgrass ecotypes shared common plastic abiotic responses to nitrogen (N) and water availability, and yet had substantial genotypic variation for root and shoot traits. A significant interaction between N and water stress combination treatments for axial and lateral root traits represents a complex and shared root development strategy for stress mitigation. Deep root growth and 15N capture were found to be closely linked to aboveground growth. Together, these results represent the wide genetic pool of switchgrass and show that deep rooting promotes nitrate capture, plant productivity, and sustainability. [ABSTRACT FROM AUTHOR]

Soil flooding creates low-oxygen environments in root zones and thus severely affects plant growth and productivity. Plants adapt to low-oxygen environments by a suite of orchestrated metabolic and anatomical alterations. Of these, formation of aerenchyma and development of adventitious roots are considered very critical to enable plant performance in waterlogged soils. Both traits have been firmly associated with stress-induced increases in ethylene levels in root tissues that operate upstream of signalling pathways. Recently, we used a bioinformatic approach to demonstrate that several Ca2+ and K+ -permeable channels from KCO, AKT, and TPC families could also operate in low oxygen sensing in Arabidopsis. Here we argue that low-oxygen-induced changes to cellular ion homeostasis and operation of membrane transporters may be critical for cell fate determination and formation of the lysigenous aerenchyma in plant roots and shaping the root architecture and adventitious root development in grasses. We summarize the existing evidence for a causal link between tissue-specific changes in oxygen concentration, intracellular Ca2+ and K+ homeostasis, and reactive oxygen species levels, and their role in conferring those two major traits enabling plant adaptation to a low-oxygen environment. We conclude that, for efficient operation, plants may rely on several complementary signalling pathway mechanisms that operate in concert and 'fine-tune' each other. A better understanding of this interaction may create additional and previously unexplored opportunities to crop breeders to improve cereal crop yield losses to soil flooding. [ABSTRACT FROM AUTHOR]

Cold stress adversely affects plant growth and is a limiting factor in crop productivity. Temperature volatility as a consequence of climate change will increase the effects of cold stress on crop cultivation. Low temperatures frequently occur early after planting in temperate climates, and severely affect root development in cereals. In this review, we address the question of how cereal root systems respond to cold at different scales. First, we summarize the morphological, physiological, and cellular responses of cereal roots to cold stress and how these processes are regulated by phytohormones. Subsequently, we highlight current understanding of the genetic and molecular analyses of cold tolerance with emphasis on the role of cold-responsive genes in improving cold tolerance in cereal roots. Finally, we discuss the role of beneficial microorganisms and mineral nutrients in ameliorating the effects of cold stress in cereal roots. A comprehensive knowledge of the molecular mechanisms underlying cold tolerance will ensure yield stability by enabling the generation of cold-tolerant crop genotypes. [ABSTRACT FROM AUTHOR]