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Summary: Stem bending in trees induces flexure wood but its properties and development are poorly understood. Here, we investigated the effects of low‐intensity multidirectional stem flexing on growth and wood properties of hybrid aspen, and on its transcriptomic and hormonal responses.Glasshouse‐grown trees were either kept stationary or subjected to several daily shakes for 5 wk, after which the transcriptomes and hormones were analyzed in the cambial region and developing wood tissues, and the wood properties were analyzed by physical, chemical and microscopy techniques.Shaking increased primary and secondary growth and altered wood differentiation by stimulating gelatinous‐fiber formation, reducing secondary wall thickness, changing matrix polysaccharides and increasing cellulose, G‐ and H‐lignin contents, cell wall porosity and saccharification yields. Wood‐forming tissues exhibited elevated jasmonate, polyamine, ethylene and brassinosteroids and reduced abscisic acid and gibberellin signaling. Transcriptional responses resembled those during tension wood formation but not opposite wood formation and revealed several thigmomorphogenesis‐related genes as well as novel gene networks including FLA and XTH genes encoding plasma membrane‐bound proteins.Low‐intensity stem flexing stimulates growth and induces wood having improved biorefinery properties through molecular and hormonal pathways similar to thigmomorphogenesis in herbaceous plants and largely overlapping with the tension wood program of hardwoods. [ABSTRACT FROM AUTHOR]

Summary: Indole‐3‐acetic acid (IAA) controls a plethora of developmental processes. Thus, regulation of its concentration is of great relevance for plant performance. Cellular IAA concentration depends on its transport, biosynthesis and the various pathways for IAA inactivation, including oxidation and conjugation.Group II members of the GRETCHEN HAGEN 3 (GH3) gene family code for acyl acid amido synthetases catalysing the conjugation of IAA to amino acids. However, the high degree of functional redundancy among them has hampered thorough analysis of their roles in plant development.In this work, we generated an Arabidopsis gh3.1,2,3,4,5,6,9,17 (gh3oct) mutant to knock out the group II GH3 pathway. The gh3oct plants had an elaborated root architecture, showed an increased tolerance to different osmotic stresses, including an IAA‐dependent tolerance to salinity, and were more tolerant to water deficit. Indole‐3‐acetic acid metabolite quantification in gh3oct plants suggested the existence of additional GH3‐like enzymes in IAA metabolism. Moreover, our data suggested that 2‐oxindole‐3‐acetic acid production depends, at least in part, on the GH3 pathway. Targeted stress‐hormone analysis further suggested involvement of abscisic acid in the differential response to salinity of gh3oct plants.Taken together, our data provide new insights into the roles of group II GH3s in IAA metabolism and hormone‐regulated plant development. [ABSTRACT FROM AUTHOR]

Summary: The levels of the important plant growth regulator indole‐3‐acetic acid (IAA) are tightly controlled within plant tissues to spatiotemporally orchestrate concentration gradients that drive plant growth and development. Metabolic inactivation of bioactive IAA is known to participate in the modulation of IAA maxima and minima.IAA can be irreversibly inactivated by oxidation and conjugation to aspartate and glutamate. Usually overlooked because of its reversible nature, the most abundant inactive IAA form is the IAA‐glucose (IAA‐glc) conjugate.Glycosylation of IAA in Arabidopsis thaliana is reported to be carried out by UDP‐glycosyltransferase 84B1 (UGT84B1), while UGT74D1 has been implicated in the glycosylation of the irreversibly formed IAA catabolite oxIAA.Here we demonstrated that both UGT84B1 and UGT74D1 modulate IAA levels throughout plant development by dual IAA and oxIAA glycosylation. Moreover, we identified a novel UGT subfamily whose members redundantly mediate the glycosylation of oxIAA and modulate skotomorphogenic growth. [ABSTRACT FROM AUTHOR]

SUMMARY: The phytohormone cytokinin plays a significant role in nearly all aspects of plant growth and development. Cytokinin signaling has primarily been studied in the dicot model Arabidopsis, with relatively little work done in monocots, which include rice (Oryza sativa) and other cereals of agronomic importance. The cytokinin signaling pathway is a phosphorelay comprised of the histidine kinase receptors, the authentic histidine phosphotransfer proteins (AHPs) and type‐B response regulators (RRs). Two negative regulators of cytokinin signaling have been identified: the type‐A RRs, which are cytokinin primary response genes, and the pseudo histidine phosphotransfer proteins (PHPs), which lack the His residue required for phosphorelay. Here, we describe the role of the rice PHP genes. Phylogenic analysis indicates that the PHPs are generally first found in the genomes of gymnosperms and that they arose independently in monocots and dicots. Consistent with this, the three rice PHPs fail to complement an Arabidopsis php mutant (aphp1/ahp6). Disruption of the three rice PHPs results in a molecular phenotype consistent with these elements acting as negative regulators of cytokinin signaling, including the induction of a number of type‐A RR and cytokinin oxidase genes. The triple php mutant affects multiple aspects of rice growth and development, including shoot morphology, panicle architecture, and seed fill. In contrast to Arabidopsis, disruption of the rice PHPs does not affect root vascular patterning, suggesting that while many aspects of key signaling networks are conserved between monocots and dicots, the roles of at least some cytokinin signaling elements are distinct. Significance Statement: We demonstrate that the function of the rice pseudo histidine phosphotransfer proteins has diverged from their Arabidopsis counterparts, despite data indicating that these rice proteins are also negative regulators of cytokinin signaling. [ABSTRACT FROM AUTHOR]

Summary: The plant hormone auxin is a key factor for regulation of plant development, and this function was probably reinforced during the evolution of early land plants. We have extended the available toolbox to allow detailed studies of how auxin biosynthesis and responses are regulated in moss reproductive organs, their stem cells and gametes to better elucidate the function of auxin in the morphogenesis of early land plants.We measured auxin metabolites and identified IPyA (indole‐3‐pyruvic acid) as the main biosynthesis pathway in Physcomitrium (Physcomitrella) patens and established knock‐out, overexpressor and reporter lines for biosynthesis genes which were analyzed alongside previously reported auxin‐sensing and transport reporters.Vegetative and reproductive apical stem cells synthesize auxin. Sustained stem cell activity depends on an inability to sense the auxin produced while progeny of the stem cells respond to the auxin, aiding in the control of cell division, expansion and differentiation. Gamete precursors are dependent on a certain degree of auxin sensing, while the final differentiation is a low auxin‐sensing process.Tha data presented indicate that low auxin activity may represent a conserved hallmark of land plant gametes, and that local auxin biosynthesis in apical stem cells may be part of an ancestral mechanism to control focal growth. [ABSTRACT FROM AUTHOR]

Summary: Dynamic regulation of the concentration of the natural auxin (IAA) is essential to coordinate most of the physiological and developmental processes and responses to environmental changes. Oxidation of IAA is a major pathway to control auxin concentrations in angiosperms and, along with IAA conjugation, to respond to perturbation of IAA homeostasis. However, these regulatory mechanisms remain poorly investigated in conifers. To reduce this knowledge gap, we investigated the different contributions of the IAA inactivation pathways in conifers.MS‐based quantification of IAA metabolites under steady‐state conditions and after perturbation was investigated to evaluate IAA homeostasis in conifers. Putative Picea abies GH3 genes (PaGH3) were identified based on a comprehensive phylogenetic analysis including angiosperms and basal land plants. Auxin‐inducible PaGH3 genes were identified by expression analysis and their IAA‐conjugating activity was explored.Compared to Arabidopsis, oxidative and conjugative pathways differentially contribute to reduce IAA concentrations in conifers. We demonstrated that the oxidation pathway plays a marginal role in controlling IAA homeostasis in spruce. By contrast, an excess of IAA rapidly activates GH3‐mediated irreversible conjugation pathways.Taken together, these data indicate that a diversification of IAA inactivation mechanisms evolved specifically in conifers. [ABSTRACT FROM AUTHOR]

The phytohormones jasmonate, gibberellin, salicylate, and ethylene regulate an interconnected reprogramming network integrating root development with plant responses against microbes. The establishment of mutualistic ectomycorrhizal symbiosis requires the suppression of plant defense responses against fungi as well as the modification of root architecture and cortical cell wall properties. Here, we investigated the contribution of phytohormones and their crosstalk to the ontogenesis of ectomycorrhizae (ECM) between grey poplar (Populus tremulax alba) roots and the fungus Laccaria bicolor. To obtain the hormonal blueprint of developing ECM, we quantified the concentrations of jasmonates, gibberellins, and salicylate via liquid chromatography–tandem mass spectrometry. Subsequently, we assessed root architecture, mycorrhizal morphology, and gene expression levels (RNA sequencing) in phytohormone‐treated poplar lateral roots in the presence or absence of L. bicolor. Salicylic acid accumulated in mid‐stage ECM. Exogenous phytohormone treatment affected the fungal colonization rate and/or frequency of Hartig net formation. Colonized lateral roots displayed diminished responsiveness to jasmonate but regulated some genes, implicated in defense and cell wall remodelling, that were specifically differentially expressed after jasmonate treatment. Responses to salicylate, gibberellin, and ethylene were enhanced in ECM. The dynamics of phytohormone accumulation and response suggest that jasmonate, gibberellin, salicylate, and ethylene signalling play multifaceted roles in poplar L. bicolor ectomycorrhizal development. The ectomycorrhizal fungus Laccaria bicolor affects sensitivity to jasmonate in roots of Populus tremulax alba, while promoting responses to salicylate, gibberellin, and ethylene. Adjusted accumulation and perception of these phytohormones is necessary for the development of ectomycorrhizae. [ABSTRACT FROM AUTHOR]

Cytokinins are an important group of plant hormones that are also found in other organisms, including cyanobacteria. While various aspects of cytokinin function and metabolism are well understood in plants, the information is limited for cyanobacteria. In this study, we first experimentally confirmed a prenylation of tRNA by recombinant isopentenyl transferase NoIPT2 from Nostoc sp. PCC 7120, whose encoding gene we previously identified in Nostoc genome along with the gene for adenylate isopentenyl transferase NoIPT1. In contrast to NoIPT2, the transcription of NoIPT1 was strongly activated during the dark period and was followed by an increase in the cytokinin content several hours later in the light period. Dominant cytokinin metabolites detected at all time points were free bases and monophosphates of isopentenyladenine and cis-zeatin, while N-glucosides were not detected at all. Whole transcriptome differential expression analysis of cultures of the above Nostoc strain treated by cytokinin compared to untreated controls indicated that cytokinin together with light trigger expression of several genes related to signal transduction, including two-component sensor histidine kinases and two-component hybrid sensors and regulators. One of the affected histidine kinases with a cyclase/histidine kinase-associated sensory extracellular domain similar to the cytokinin-binding domain in plant cytokinin receptors was able to modestly bind isopentenyladenine. The data show that the genetic disposition allows Nostoc not only to produce free cytokinins and prenylate tRNA but also modulate the cytokinin biosynthesis in response to light, triggering complex changes in sensing and regulation. [ABSTRACT FROM AUTHOR]