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Roots are fundamental for plants to adapt to variable environmental conditions. The development of a robust root system is orchestrated by numerous genetic determinants and, among them, the MADS‐box gene ANR1 has garnered substantial attention. Prior research has demonstrated that, in chrysanthemum, CmANR1 positively regulates root system development. Nevertheless, the upstream regulators involved in the CmANR1‐mediated regulation of root development remain unidentified. In this study, we successfully identified bric‐a‐brac, tramtrack and broad (BTB) and transcription adapter putative zinc finger (TAZ) domain protein CmBT1 as the interacting partner of CmANR1 through a yeast‐two‐hybrid (Y2H) screening library. Furthermore, we validated this physical interaction through bimolecular fluorescence complementation and pull‐down assays. Functional assays revealed that CmBT1 exerted a negative influence on root development in chrysanthemum. In both in vitro and in vivo assays, it was evident that CmBT1 mediated the ubiquitination of CmANR1 through the ubiquitin/26S proteasome pathway. This ubiquitination subsequently led to the degradation of the CmANR1 protein and a reduction in the transcription of CmANR1‐targeted gene CmPIN2, which was crucial for root development in chrysanthemum. Genetic analysis suggested that CmBT1 modulated root development, at least in part, by regulating the level of CmANR1 protein. Collectively, these findings shed new light on the regulatory role of CmBT1 in degrading CmANR1 through ubiquitination, thereby repressing the expression of its targeted gene and inhibiting root development in chrysanthemum. [ABSTRACT FROM AUTHOR]

Chrysanthemum, one of the most popular ornamental plants in the world, is renowned for its brilliant colors and multifarious flower types. Thousands of gorgeous chrysanthemum cultivars exist thanks to both traditional breeding techniques and its characteristic bud sporting. In this study, we identified a pink-to-yellow flower color-changed bud sport of the edible chrysanthemum cultivar 'Pink Candy'. The bud variant and its parent plant bloomed at the same time, but with yellow- and pink-colored flowers, respectively. However, the two flower types exhibited strikingly different combinations and concentrations of primary and secondary metabolites, aromatic compounds, and pigments. Additionally, the expression patterns of key pigment biosynthesis genes, such as CmPAL (phenylalanineammonialyase), CmDFR (dihydroflavonol 4-reductase), CmF3H (flavanone 3′-hydroxylase), CmNXS (neoxanthin synthase) and CmCCD4 (carotenoid cleavage dioxygenase 4) were distinct between both flower types, helping to explain the color transformation of the mutant to some extent. Taken together, our results suggest a mechanism explaining the transformation of pink flowers to yellow flowers in the mutant bud sport. These results provide the foundation for the production of a novel chrysanthemum cultivar. [ABSTRACT FROM AUTHOR]

Flower color, a critical phenotypic trait of ornamental plants, is an essential indicator for flower variety classification. Many physical and internal factors that affect flower color have been widely investigated; however, the effects of internal factors during the flowering period remain unknown. In this study, we evaluated the effects of internal factors on floral coloration during the flowering period of four chrysanthemum cultivars of different colors. colorimetric measurements showed that L*, a*, and b* were in correlation with the lightness and color development in the four chrysanthemum cultivars. The distinctive shape of upper epidermal cells was observed in each flowering stage of different colored chrysanthemums. With progression of the flowering process, the content of anthocyanins and carotenoids increased during early stages, decreased at the senescence stage, and was the highest at the full-bloom stage. The vacuolar pH of flowers gradually decreased as the flower bloomed. Metal contents in flowers varied across different chrysanthemum varieties. Anthocyanins biosynthesis genes, such as CmCHS and CmCHI, were expressed and responsible for pigment changes in red chrysanthemums. Moreover, the expression pattern of cytosol pH-related genes, such as CmVHA-a1, CmVHA-C, and CmVHA-C″1, was in accordance with a decrease in pH during flowering stages. Our results revealed the effects of main internal factors on floral color during the flowering period in four Chrysanthemum varieties, providing insights into the introcellular and molecular regulatory mechanisms of flower coloration and laying key foundations for the improvement of color breeding in chrysanthemums. [ABSTRACT FROM AUTHOR]

Sugars are involved in plant growth, fruit quality, and signaling perception. Therefore, understanding the mechanisms involved in soluble sugar accumulation is essential to understand fruit development. Here, we report that MdPFPβ, a pyrophosphate‐dependent phosphofructokinase gene, regulates soluble sugar accumulation by enhancing the photosynthetic performance and sugar‐metabolizing enzyme activities in apple (Malus domestica Borkh.). Biochemical analysis revealed that a basic helix‐loop‐helix (bHLH) transcription factor, MdbHLH3, binds to the MdPFPβ promoter and activates its expression, thus promoting soluble sugar accumulation in apple fruit. In addition, MdPFPβ overexpression in tomato influenced photosynthesis and carbon metabolism in the plant. Furthermore, we determined that MdbHLH3 increases photosynthetic rates and soluble sugar accumulation in apple by activating MdPFPβ expression. Our results thus shed light on the mechanism of soluble sugar accumulation in apple leaves and fruit: MdbHLH3 regulates soluble sugar accumulation by activating MdPFPβ gene expression and coordinating carbohydrate allocation. [ABSTRACT FROM AUTHOR]

Summary: Changes in carbohydrates and organic acids largely determine the palatability of edible tissues of horticulture crops. Elucidating the potential molecular mechanisms involved in the change in carbohydrates and organic acids, and their temporal and spatial crosstalk are key steps in understanding fruit developmental processes. Here, we used apple (Malus domestica Borkh.) as research materials and found that MdbHLH3, a basic helix–loop–helix transcription factor (bHLH TF), modulates the accumulation of malate and carbohydrates. Biochemical analyses demonstrated that MdbHLH3 directly binds to the promoter of MdcyMDH that encodes an apple cytosolic NAD‐dependent malate dehydrogenase, activating its transcriptional expression, thereby promoting malate accumulation in apple fruits. Additionally, MdbHLH3 overexpression increased the photosynthetic capacity and carbohydrate levels in apple leaves and also enhanced the carbohydrate accumulation in fruits by adjusting carbohydrate allocation from sources to sinks. Overall, our findings provide new insights into the mechanism of how the bHLH TF MdbHLH3 modulates the fruit quality. It directly regulates the expression of cytosolic malate dehydrogenase MdcyMDH to coordinate carbohydrate allocation and malate accumulation in apple. [ABSTRACT FROM AUTHOR]

Lateral root (LR) formation and development play a vital role in plant development by permitting the establishment of branched root systems. It is well known that nutrient availability controls LR development. Moreover, LR development is fine-tuned by a myriad of hormonal signals. Many transcription factors (TFs) participate in LR development. Here, we discuss the TFs involved in the nitrate and auxin signaling pathways and how these function in the regulation of LR formation and development in chrysanthemum. AtTCP20 is a plant-specific TF, which can modulate LR development in response to nitrate. The roles of CmTCP20 in LR development were identified by overexpression in chrysanthemum and heterologous expression in Arabidopsis. Overexpression of CmTCP20 significantly increased the number and average length of LRs compared with the wild type in chrysanthemum and Arabidopsis. We also found that CmTCP20 positively influenced auxin accumulation in the LRs at least partly by improving auxin biosynthesis, transport and response, thereby promoting LR development. Moreover, we found that CmTCP20 interacts with an auxin response factor, CmARF8, which also can be induced by nitrate and combined to proximal sites in the upstream promoter region of CmCYCB1;1 to positively regulate the cell cycle. The CmTCP20-CmARF8 heterodimer links nitrate and auxin signaling and converts cell-cycle signals to regulate LR initiation and growth. [ABSTRACT FROM AUTHOR]

Background: The roles in photosystem I (PSI) assembly of the nucleus-encoded thylakoid protein Y3IP1 who interacts with the plastid-encoded Ycf3 protein that has been well-characterized in plants. However, its function and potential mechanisms in other aspects remain poorly understood. Results: We identified the apple MdY3IP1 gene, which encodes a protein highly homologous to the Arabidopsis Y3IP1 (AtY3IP1). Ectopic expression of MdY3IP1 triggered early-flowering and enhanced salt tolerance in Arabidopsis plants. MdY3IP1 controlled floral transition by accelerating sugar metabolism process in plant cells, thereby influencing the expression of flowering-associated genes. The increase in salt stress tolerance in MdY3IP1-expressing plants correlated with reduced reactive oxygen species (ROS) accumulation, and an increase in lateral root development by regulating both auxin biosynthesis and transport, as followed by enhancement of salt tolerance in Arabidopsis. Overall, these findings provide new evidences for additional functions of Y3IP1-like proteins and their underlying mechanisms of which Y3IP1 confers early-flowering and salt tolerance phenotypes in plants. Conclusions: These observations suggest that plant growth and stress resistance can be affected by the regulation of the MdY3IP1 gene. Further molecular and genetic approaches will accelerate our knowledge of MdY3IP1 functions in PSI complex formation and plants stress resistance, and inform strategies for creating transgenic crop varieties with early maturity and high-resistant to adverse environmental conditions. [ABSTRACT FROM AUTHOR]

Root system architecture is an important agronomic trait by which plants both acquire water and nutrients from the soil and adapt to survive in a complex environment. The adaptation of plant root systems to environmental constraints largely depends on the growth and development of lateral roots (LRs). MADS-box transcription factors (TFs) are important known regulators of plant growth, development, and response to environmental stimuli. However, the potential mechanisms by which they regulate LRs development remain poorly understood. Here, we identified a MADS-box chrysanthemum gene CmANR1 , homologous to the Arabidopsis gene AtANR1 , which plays a key role in the regulation of LR development. qRT-PCR assays indicated that CmANR1 was primarily expressed in chrysanthemum roots and was rapidly induced by exposure to high nitrate concentrations. Ectopic expression of CmANR1 in Arabidopsis significantly increased the number and length of emerged LRs compared to the wild-type (col) control, but had no obvious affect on primary root (PR) development. We also found that CmANR1 positively influenced auxin accumulation in LRs at least partly by improving auxin biosynthesis and transport, thereby promoting LR development. Furthermore, we found that ANR1 formed homo- and heterodimers through interactions with itself and AGL21 at its C-terminal domain. Overall, our findings provide considerable new information about the mechanisms by which the chrysanthemum MADS-box TF CmANR1 mediates LR development by directly altering auxin accumulation. [ABSTRACT FROM AUTHOR]

Malate, the predominant organic acid in many fruits, is a crucial component of the organoleptic quality of fruit, including taste and flavor. The genetic and environmental mechanisms affecting malate metabolism in fruit cells have been studied extensively. However, the transcriptional regulation of malate-metabolizing enzymes and vacuolar transporters remains poorly understood. Our previous studies demonstrated that Md MYB1 modulates anthocyanin accumulation and vacuolar acidification by directly activating vacuolar transporters, including Md VHA-B1, Md VHA-E, Md VHP1 and Mdt DT. Interestingly, we isolated and identified a MYB transcription factor, Md MYB73, a distant relative of Md MYB1 in this study. It was subsequently found that Md MYB73 protein bound directly to the promoters of Md ALMT9 (aluminum-activated malate transporter 9), Md VHA-A (vacuolar ATPase subunit A) and Md VHP1 (vacuolar pyrophosphatase 1), transcriptionally activating their expression and thereby enhancing their activities. Analyses of transgenic apple calli demonstrated that Md MYB73 influenced malate accumulation and vacuolar pH. Furthermore, Md CIb HLH1 interacted with Md MYB73 and enhanced its activity upon downstream target genes. These findings help to elucidate how Md MYB73 directly modulates the vacuolar transport system to affect malate accumulation and vacuolar pH in apple. [ABSTRACT FROM AUTHOR]

Glucose induces anthocyanin accumulation in many plant species; however, the molecular mechanism involved in this process remains largely unknown. Here, we found that apple hexokinase MdHXK1, a glucose sensor, was involved in sensing exogenous glucose and regulating anthocyanin biosynthesis. In vitro and in vivo assays suggested that MdHXK1 interacted directly with and phosphorylated an anthocyanin-associated bHLH transcription factor (TF) MdbHLH3 at its Ser361 site in response to glucose. Furthermore, both the hexokinase_2 domain and signal peptide are crucial for the MdHXK1-mediated phosphorylation of MdbHLH3. Moreover, phosphorylation modification stabilized MdbHLH3 protein and enhanced its transcription of the anthocyanin biosynthesis genes, thereby increasing anthocyanin biosynthesis. Finally, a series of transgenic analyses in apple calli and fruits demonstrated that MdHXK1 controlled glucose-induced anthocyanin accumulation at least partially, if not completely, via regulating MdbHLH3. Overall, our findings provide new insights into the mechanism of the glucose sensor HXK1 modulation of anthocyanin accumulation, which occur by directly regulating the anthocyanin-related bHLH TFs in response to a glucose signal in plants. [ABSTRACT FROM AUTHOR]

Vacuolar H + -ATPase (V-H + -ATPase) is highly conserved, multisubunit proton pumps that play key roles in adaptation to abiotic stress in plants. Function of apple V-ATPase subunit B1 ( MdVHA-B1 ) has been identified in drought tolerance, however, it remains unclear whether MdVHA-B1 is involved in salt tolerance. In this work, we characterized the function of MdVHA-B1 gene in salt stress response. GUS and Western blotting assays showed that MdVHA-B1 was highly induced by salt stress. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays demonstrated that MdVHA-B1 interacts with MdSOS2L1, a Arabidopsis SOS2-like protein kinase, in apple. Compared with wild-type (WT) apple calli, V-ATPase activities in the transgenic calli were significantly enhanced under salt stress condition. Furthermore, Na + and K + were accumulated much higher in transgenic tomato plants than the WT control. These results suggest that MdVHA-B1 may confer salt tolerance through salt overly sensitive (SOS) signal pathway in apple to regulate the ion balance. [ABSTRACT FROM AUTHOR]

Nitrogen is very important to the yield and quality of chrysanthemum. However, excessive application not only negatively affects the yield and quality of chrysanthemum, but also can not be timely absorbed and utilized for chrysanthemum, so causes a lot of waste of fertilizer resources and serious pollution of groundwater environment. Nitrate nitrogen is the main form of nitrogen uptake by the roots of chrysanthemum. The uptake of NO 3 − by plants is mostly achieved by NO 3 − transporters (NRTs) and lateral root formation. However, the morphological structure and molecular mechanism of the response to nitrate signaling in the roots of chrysanthemum are poorly understood. In this study, we investigated that the response to NO 3 − signaling from the viewpoint of roots morphology and anatomical structure, roots NO 3 − contents, endogenous hormones contents and expression of related genes in the roots of chrysanthemum. A hydroponic experiment was performed using the rooted cuttings of chrysanthemum, with KNO 3 treatments (control for Hogland nutrient solution without N element) for seven times at 0, 1, 2, 3, 4, 5, 6 days, respectively. The results showed that the roots morphological indexes increased significantly in the KNO 3 treatments compared to those of the controls at 6 days after treatments, which were associated with the high expression of CmNRT1.1 , CmNRT2.1 , CmNAR2.1 and CmANR1 , which related to NO 3 − transport genes and lateral root development gene, the contents of NO 3 − , indole-3-acetic acid (IAA) and cytokinin (CTK) in the roots and the improved root microscopic structure in KNO 3 treatment. The promoting effect of KNO 3 shows an obvious time-effect. The results from correlation analysis indicated that the responses of chrysanthemum root to NO 3 − signaling could be related with the induction of NO 3 − signaling, the gene expression of NO 3 − transporter genes and lateral root development gene due to regulating the IAA, CTK levels and adjusting the root architecture of the root system. [ABSTRACT FROM AUTHOR]

Sugars are essential regulatory molecules involved in plant growth and development and defense response. Although the relationship between sugars and disease resistance has been widely discussed, the underlying molecular mechanisms remain unexplored. Ring rot caused by Botryosphaeria dothidea (B. dothidea), which severely affects fruit quality and yield, is a destructive disease of apples (Malus domestica Borkh.). The present study found that the degree of disease resistance in apple fruit was closely related to glucose content. Therefore, the gene encoding a hexokinase, MdHXK1, was isolated from the apple cultivar 'Gala', and characterized during the defense response. Overexpression of MdHXK1 enhanced disease resistance in apple calli, leaves and fruits by increasing the expression levels of genes related to salicylate (SA) synthesis (PHYTOALEXIN DEFICIENT 4, PAD4; PHENYLALANINE AMMONIA-LYASE, PAL; and ENHANCED DISEASE SUSCEPTIBILITY 1, EDS1) and signaling (PR1; PR5; and NONEXPRESSER OF PR GENES 1, NPR1) as well as increasing the superoxide (O 2- ) production rate and the hydrogen peroxide (H 2 O 2 ) content. Overall, the study provides new insights into the MdHXK1-mediated molecular mechanisms by which glucose signaling regulates apple ring rot resistance., (© 2021 Scandinavian Plant Physiology Society.)

Background: The roles in photosystem I (PSI) assembly of the nucleus-encoded thylakoid protein Y3IP1 who interacts with the plastid-encoded Ycf3 protein that has been well-characterized in plants. However, its function and potential mechanisms in other aspects remain poorly understood., Results: We identified the apple MdY3IP1 gene, which encodes a protein highly homologous to the Arabidopsis Y3IP1 (AtY3IP1). Ectopic expression of MdY3IP1 triggered early-flowering and enhanced salt tolerance in Arabidopsis plants. MdY3IP1 controlled floral transition by accelerating sugar metabolism process in plant cells, thereby influencing the expression of flowering-associated genes. The increase in salt stress tolerance in MdY3IP1-expressing plants correlated with reduced reactive oxygen species (ROS) accumulation, and an increase in lateral root development by regulating both auxin biosynthesis and transport, as followed by enhancement of salt tolerance in Arabidopsis. Overall, these findings provide new evidences for additional functions of Y3IP1-like proteins and their underlying mechanisms of which Y3IP1 confers early-flowering and salt tolerance phenotypes in plants., Conclusions: These observations suggest that plant growth and stress resistance can be affected by the regulation of the MdY3IP1 gene. Further molecular and genetic approaches will accelerate our knowledge of MdY3IP1 functions in PSI complex formation and plants stress resistance, and inform strategies for creating transgenic crop varieties with early maturity and high-resistant to adverse environmental conditions.

Malate, the predominant organic acid in many fruits, is a crucial component of the organoleptic quality of fruit, including taste and flavor. The genetic and environmental mechanisms affecting malate metabolism in fruit cells have been studied extensively. However, the transcriptional regulation of malate-metabolizing enzymes and vacuolar transporters remains poorly understood. Our previous studies demonstrated that MdMYB1 modulates anthocyanin accumulation and vacuolar acidification by directly activating vacuolar transporters, including MdVHA-B1, MdVHA-E, MdVHP1 and MdtDT. Interestingly, we isolated and identified a MYB transcription factor, MdMYB73, a distant relative of MdMYB1 in this study. It was subsequently found that MdMYB73 protein bound directly to the promoters of MdALMT9 (aluminum-activated malate transporter 9), MdVHA-A (vacuolar ATPase subunit A) and MdVHP1 (vacuolar pyrophosphatase 1), transcriptionally activating their expression and thereby enhancing their activities. Analyses of transgenic apple calli demonstrated that MdMYB73 influenced malate accumulation and vacuolar pH. Furthermore, MdCIbHLH1 interacted with MdMYB73 and enhanced its activity upon downstream target genes. These findings help to elucidate how MdMYB73 directly modulates the vacuolar transport system to affect malate accumulation and vacuolar pH in apple., (© 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.)

Root plasticity is an important trait for plants to forage nutrient and adapt to survival in a complicated environment. Lateral roots (LRs) are generally more sensitive than primary roots in response to changing environmental conditions. As the main source of nitrogen for most higher plants, nitrate acting as a signal has received great attention in the regulation of LR development. In general, there are dual effects including stimulatory and inhibitory of low nitrate on LR development; while high nitrate supply has an inhibitory effect on LR development; nitrate heterogeneity also has a stimulatory effect on LR development in [Formula: see text]- rich zone. Here, we focus on recent progresses in the role of a nitrate signal in the regulation of the LRs development.

Soil salinity hinders the growth of most higher plants and becomes a gradually increasing threat to the agricultural production of such crops as the woody plant apple. In this study, a calcineurin B-like protein (CBL)-interacting protein kinase, MdCIPK24-LIKE1 (named as MdSOS2L1), was identified. Quantitative real-time polymerase chain reaction (qRT-PCR) assay revealed that the expression of MdSOS2L1 was upregulated by CaCl 2 . Yeast two-hybrid (Y2H) assay and transiently transgenic analysis demonstrated that the MdSOS2L1 protein kinase physically interacted with MdCBL1, MdCBL4 and MdCBL10 proteins to increase salt tolerance in apple. Furthermore, iTRAQ proteome combined with liquid chromatography-tandem mass spectrometry (LC/MS) analysis found that several proteins, which are involved in reactive oxygen species (ROS) scavenging, procyanidin biosynthesis and malate metabolism, were induced in MdSOS2L1-overexpressing apple plants. Subsequent studies have shown that MdSOS2L1 increased antioxidant metabolites such as procyanidin and malate to improve salt tolerance in apple and tomato. In summary, our studies provide a mechanism in which SOS2L1 enhances the salt stress tolerance in apple and tomato., (© 2015 Scandinavian Plant Physiology Society.)