MYB-related transcription factors control chloroplast biogenesis.

Chloroplast biogenesis is dependent on master regulators from the GOLDEN2-LIKE (GLK) family of transcription factors. However, glk mutants contain residual chlorophyll, indicating that other proteins must be involved. Here, we identify MYB-related transcription factors as regulators of chloroplast biogenesis in the liverwort Marchantia polymorpha and angiosperm Arabidopsis thaliana. In both species, double-mutant alleles in MYB-related genes show very limited chloroplast development, and photosynthesis gene expression is perturbed to a greater extent than in GLK mutants. Genes encoding enzymes of chlorophyll biosynthesis are controlled by MYB-related and GLK proteins, whereas those allowing CO2 fixation, photorespiration, and photosystem assembly and repair require MYB-related proteins. Regulation between the MYB-related and GLK transcription factors appears more extensive in A. thaliana than in M. polymorpha. Thus, MYB-related and GLK genes have overlapping as well as distinct targets. We conclude that MYB-related and GLK transcription factors orchestrate chloroplast development in land plants.

A Natural Allele of a Transcription Factor in Rice Confers Broad-Spectrum Blast Resistance.

Rice feeds half the world's population, and rice blast is often a destructive disease that results in significant crop loss. Non-race-specific resistance has been more effective in controlling crop diseases than race-specific resistance because of its broad spectrum and durability. Through a genome-wide association study, we report the identification of a natural allele of a C2H2-type transcription factor in rice that confers non-race-specific resistance to blast. A survey of 3,000 sequenced rice genomes reveals that this allele exists in 10% of rice, suggesting that this favorable trait has been selected through breeding. This allele causes a single nucleotide change in the promoter of the bsr-d1 gene, which results in reduced expression of the gene through the binding of the repressive MYB transcription factor and, consequently, an inhibition of H2O2 degradation and enhanced disease resistance. Our discovery highlights this novel allele as a strategy for breeding durable resistance in rice.

DREAM On: Cell Cycle Control in Development and Disease.

Perfectly orchestrated periodic gene expression during cell cycle progression is essential for maintaining genome integrity and ensuring that cell proliferation can be stopped by environmental signals. Genetic and proteomic studies during the past two decades revealed remarkable evolutionary conservation of the key mechanisms that control cell cycle-regulated gene expression, including multisubunit DNA-binding DREAM complexes. DREAM complexes containing a retinoblastoma family member, an E2F transcription factor and its dimerization partner, and five proteins related to products of Caenorhabditis elegans multivulva (Muv) class B genes lin-9, lin-37, lin-52, lin-53, and lin-54 (comprising the MuvB core) have been described in diverse organisms, from worms to humans. This review summarizes the current knowledge of the structure, function, and regulation of DREAM complexes in different organisms, as well as the role of DREAM in human disease.

Caenorhabditis elegans telomere-binding proteins TEBP-1 and TEBP-2 adapt the Myb module to dimerize and bind telomeric DNA.

Protecting chromosome ends from misrecognition as double-stranded (ds) DNA breaks is fundamental to eukaryotic viability. The protein complex shelterin prevents a DNA damage response at mammalian telomeres. Mammalian shelterin proteins TRF1 and TRF2 and their homologs in yeast and protozoa protect telomeric dsDNA. N-terminal homodimerization and C-terminal Myb-domain-mediated dsDNA binding are two structural hallmarks of end protection by TRF homologs. Yet our understanding of how Caenorhabditis elegans protects its telomeric dsDNA is limited. Recently identified C. elegans proteins TEBP-1 (also called DTN-1) and TEBP-2 (also called DTN-2) are functional homologs of TRF proteins, but how they bind DNA and whether or how they dimerize is not known. TEBP-1 and TEBP-2 harbor three Myb-containing domains (MCDs) and no obvious dimerization domain. We demonstrate biochemically that only the third MCD binds DNA. We solve the X-ray crystal structure of TEBP-2 MCD3 with telomeric dsDNA to reveal the structural mechanism of telomeric dsDNA protection in C. elegans. Mutagenesis of the DNA-binding site of TEBP-1 and TEBP-2 compromises DNA binding in vitro, and increases DNA damage signaling, lengthens telomeres, and decreases brood size in vivo. Via an X-ray crystal structure, biochemical validation of the dimerization interface, and SEC-MALS analysis, we demonstrate that MCD1 and MCD2 form a composite dimerization module that facilitates not only TEBP-1 and TEBP-2 homodimerization but also heterodimerization. These findings provide fundamental insights into C. elegans telomeric dsDNA protection and highlight how different eukaryotes have evolved distinct strategies to solve the chromosome end protection problem.

Coordinating gene expression during the cell cycle.

Cell cycle-dependent gene transcription is tightly controlled by the retinoblastoma (RB):E2F and DREAM complexes, which repress all cell cycle genes during quiescence. Cyclin-dependent kinase (CDK) phosphorylation of RB and DREAM allows for the expression of two gene sets. The first set of genes, with peak expression in G1/S, is activated by E2F transcription factors (TFs) and is required for DNA synthesis. The second set, with maximum expression during G2/M, is required for mitosis and is coordinated by the MuvB complex, together with B-MYB and Forkhead box M1 (FOXM1). In this review, we summarize the key findings that established the distinct control mechanisms regulating G1/S and G2/M gene expression in mammals and discuss recent advances in the understanding of the temporal control of these genes.

Cyclin A participates in the TSO1-MYB3R1 regulatory module to maintain shoot meristem size and fertility in Arabidopsis.

The stem cell pools at the shoot apex and root tip give rise to all the above- and below-ground tissues of a plant. Previous studies in Arabidopsis identified a TSO1-MYB3R1 transcriptional module that controls the number and size of the stem cell pools at the shoot apex and root tip. As TSO1 and MYB3R1 are homologous to components of an animal cell cycle regulatory complex, DREAM, Arabidopsis mutants of TSO1 and MYB3R1 provide valuable tools for investigations into the link between cell cycle regulation and stem cell maintenance in plants. In this study, an Arabidopsis cyclin A gene, CYCA3;4, was identified as a member of the TSO1-MYB3R1 regulatory module and cyca3;4 mutations suppressed the tso1-1 mutant phenotype specifically in the shoot. The work reveals how the TSO1-MYB3R1 module is integrated with the cell cycle machinery to control cell division at the shoot meristem.

Effector Regulatory T Cell Differentiation and Immune Homeostasis Depend on the Transcription Factor Myb.

FoxP3-expressing regulatory T (Treg) cells are essential for maintaining immune homeostasis. Activated Treg cells undergo further differentiation into an effector state that highly expresses genes critical for Treg cell function, although how this process is coordinated on a transcriptional level is poorly understood. Here, we demonstrate that mice lacking the transcription factor Myb in Treg cells succumbed to a multi-organ inflammatory disease. Myb was specifically expressed in, and required for the differentiation of, thymus-derived effector Treg cells. The combination of transcriptome and genomic footprint analyses revealed that Myb directly regulated a large proportion of the gene expression specific to effector Treg cells, identifying Myb as a critical component of the gene regulatory network controlling effector Treg cell differentiation and function.

The SmMYC2-SmMYB36 complex is involved in methyl jasmonate-mediated tanshinones biosynthesis in Salvia miltiorrhiza.

The jasmonic acid (JA) signaling pathway plays an important role in promoting the biosynthesis of tanshinones. While individual transcription factors have been extensively studied in the context of tanshinones biosynthesis regulation, the influence of methyl jasmonate (MeJA)-induced transcriptional complexes remains unexplored. This study elucidates the positive regulatory role of the basic helix-loop-helix protein SmMYC2 in tanshinones biosynthesis in Salvia miltiorrhiza. SmMYC2 not only binds to SmGGPPS1 promoters, activating their transcription, but also interacts with SmMYB36. This interaction enhances the transcriptional activity of SmMYC2 on SmGGPPS1, thereby promoting tanshinones biosynthesis. Furthermore, we identified three JA signaling repressors, SmJAZ3, SmJAZ4, and SmJAZ8, which interact with SmMYC2. These repressors hindered the transcriptional activity of SmMYC2 on SmGGPPS1 and disrupted the interaction between SmMYC2 and SmMYB36. MeJA treatment triggered the degradation of SmJAZ3 and SmJAZ4, allowing the SmMYC2-SmMYB36 complex to subsequently activate the expression of SmGGPPS1, whereas SmJAZ8 inhibited MeJA-mediated degradation due to the absence of the LPIARR motif. These results demonstrate that the SmJAZ-SmMYC2-SmMYB36 module dynamically regulates the JA-mediated accumulation of tanshinones. Our results reveal a new regulatory network for the biosynthesis of tanshinones. This study provides valuable insight for future research on MeJA-mediated modulation of tanshinones biosynthesis.

LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) partially inhibits the transcriptional activation of FT by MYB73 and regulates flowering in Arabidopsis.

Polycomb group (PcG) proteins are essential gene repressors in higher eukaryotes. However, how PcG proteins mediate transcriptional regulation of specific genes remains unknown. LIKE HETEROCHROMATIN PROTEIN 1 (LHP1), as a component of Polycomb Repression Complexes (PRC), epigenetically mediates several plant developmental processes together with PcG proteins. We observed physical interaction between MYB73 and LHP1 in vitro and in vivo. Genetic analysis indicated that myb73 mutants showed slightly late flowering, and the lhp1-3 myb73-2 double mutant exhibited delayed flowering and downregulated FT expression compared to lhp1-3. Chromatin immunoprecipitation and yeast one-hybrid assays revealed that MYB73 preferentially binds to the FT promoter. Additionally, our protoplast transient assays demonstrated that MYB73 activates to the FT promoter. Interestingly, the LHP1-MYB73 interaction is necessary to repress the FT promoter, suggesting that the LHP1-MYB73 interaction prevents FT activation by MYB73 in Arabidopsis. Our results show an example in which a chromatin regulator affects transcriptional regulation by negatively regulating a transcription factor through direct interaction.

Comparative and functional analysis unveils the contribution of photoperiod to DNA methylation, sRNA accumulation, and gene expression variations in short-day and long-day grasses.

Photoperiod employs complicated networks to regulate various developmental processes in plants, including flowering transition. However, the specific mechanisms by which photoperiod affects epigenetic modifications and gene expression variations in plants remain elusive. In this study, we conducted a comprehensive analysis of DNA methylation, small RNA (sRNA) accumulation, and gene expressions under different daylengths in facultative long-day (LD) grass Brachypodium distachyon and short-day (SD) grass rice. Our results showed that while overall DNA methylation levels were minimally affected by different photoperiods, CHH methylation levels were repressed under their favorable light conditions, particularly in rice. We identified numerous differentially methylated regions (DMRs) that were influenced by photoperiod in both plant species. Apart from differential sRNA clusters, we observed alterations in the expression of key components of the RNA-directed DNA methylation pathway, DNA methyltransferases, and demethylases, which may contribute to the identified photoperiod-influenced CHH DMRs. Furthermore, we identified many differentially expressed genes in response to different daylengths, some of which were associated with the DMRs. Notably, we discovered a photoperiod-responsive gene MYB11 in the transcriptome of B. distachyon, and further demonstrated its role as a flowering inhibitor by repressing FT1 transcription. Together, our comparative and functional analysis sheds light on the effects of daylength on DNA methylation, sRNA accumulation, and gene expression variations in LD and SD plants, thereby facilitating better designing breeding programs aimed at developing high-yield crops that can adapt to local growing seasons.

Restricted responses of AcMYB68 and AcERF74/75 enhanced waterlogging tolerance in kiwifruit.

Most of kiwifruit cultivars (e.g. Actinidia chinensis cv. Donghong, "DH") were sensitive to waterlogging, thus, waterlogging resistant rootstocks (e.g. Actinidia valvata Dunn, "Dunn") were widely used for kiwifruit industry. Those different species provided ideal materials to understand the waterlogging responses in kiwifruit. Compared to the weaken growth and root activities in "DH", "Dunn" maintained the relative high root activities under the prolonged waterlogging. Based on comparative analysis, transcript levels of pyruvate decarboxylase (PDCs) and alcohol dehydrogenase (ADHs) showed significantly difference between these two species. Both PDCs and ADHs had been significantly increased by waterlogging in "DH", while they were only limitedly triggered by 2 days stress and subsided during the prolonged waterlogging in "Dunn". Thus, 19 differentially expressed transcript factors (DETFs) had been isolated using weighted gene co-expression network analysis combined with transcriptomics and transcript levels of PDCs and ADHs in waterlogged "DH". Among these DETFs, dual luciferase and electrophoretic mobility shift assays indicated AcMYB68 could bind to and trigger the activity of AcPDC2 promoter. The stable over-expression of AcMYB68 significantly up-regulated the transcript levels of PDCs but inhibited the plant growth, especially the roots. Moreover, the enzyme activities of PDC in 35S::AcMYB68 were significantly enhanced during the waterlogging response than that in wild type plants. Most interestingly, comparative analysis indicated that the expression patterns of AcMYB68 and the previously characterized AcERF74/75 (the direct regulator on ADHs) either showed no responses (AcMYB68 and AcERF74) or very limited response (AcERF75) in "Dunn". Taken together, the restricted responses of AcMYB68 and AcERF74/75 in "Dunn" endow its waterlogging tolerance.

Jasmonate activates secondary cell wall biosynthesis through MYC2-MYB46 module.

Formation of secondary cell wall (SCW) is tightly regulated spatiotemporally by various developmental and environmental signals. Successful fine-tuning of the trade-off between SCW biosynthesis and stress responses requires a better understanding of how plant growth is regulated under environmental stress conditions. However, the current understanding of the interplay between environmental signaling and SCW formation is limited. The lipid-derived plant hormone jasmonate (JA) and its derivatives are important signaling components involved in various physiological processes including plant growth, development, and abiotic/biotic stress responses. Recent studies suggest that JA is involved in SCW formation but the signaling pathway has not been studied for how JA regulates SCW formation. We tested this hypothesis using the transcription factor MYB46, a master switch for SCW biosynthesis, and JA treatments. Both the transcript and protein levels of MYB46, a master switch for SCW formation, were significantly increased by JA treatment, resulting in the upregulation of SCW biosynthesis. We then show that this JA-induced upregulation of MYB46 is mediated by MYC2, a central regulator of JA signaling, which binds to the promoter of MYB46. We conclude that this MYC2-MYB46 module is a key component of the plant response to JA in SCW formation.

Bacillus B2 promotes root growth and enhances phosphorus absorption in apple rootstocks by affecting MhMYB15.

Due to the chelation of phosphorus in the soil, it becomes unavailable for plant growth and development. The mechanisms by which phosphorus-solubilizing bacteria activate immobilized phosphorus to promote the growth and development of woody plants, as well as the intrinsic molecular mechanisms, are not clear. Through the analysis of microbial communities in the rhizosphere 16S V3-V4 and a homologous gene encoding microbial alkaline phosphomonoesterase (phoD) in phosphate-efficient (PE) and phosphate-inefficient apple rootstocks, it was found that PE significantly enriched beneficial rhizobacteria. The best phosphorus-solubilizing bacteria, Bacillus sp. strain 7DB1 (B2), was isolated, purified, and identified from the rhizosphere soil of PE rootstocks. Incubating with Bacillus B2 into the rhizosphere of apple rootstocks significantly increased the soluble phosphorus and flavonoid content in the rhizosphere soil. Simultaneously, this process stimulates the root development of the rootstocks and enhances plant phosphorus uptake. After root transcriptome sequencing, candidate transcription factor MhMYB15, responsive to Bacillus B2, was identified through heatmap and co-expression network analysis. Yeast one-hybrid, electrophoretic mobility shift assay, and LUC assay confirmed that MhMYB15 can directly bind to the promoter regions of downstream functional genes, including chalcone synthase MhCHS2 and phosphate transporter MhPHT1;15. Transgenic experiments with MhMYB15 revealed that RNAi-MhMYB15 silenced lines failed to induce an increase in flavonoid content and phosphorus levels in the roots under the treatment of Bacillus B2, and plant growth was slower than the control. In conclusion, MhMYB15 actively responds to Bacillus B2, regulating the accumulation of flavonoids and the uptake of phosphorus, thereby influencing plant growth and development.

EpMYB2 positively regulates chicoric acid biosynthesis by activating both primary and specialized metabolic genes in purple coneflower.

Chicoric acid is the major active ingredient of the world-popular medicinal plant purple coneflower (Echinacea purpurea (L.) Menoch). It is recognized as the quality index of commercial hot-selling Echinacea products. While the biosynthetic pathway of chicoric acid in purple coneflower has been elucidated recently, its regulatory network remains elusive. Through co-expression and phylogenetic analysis, we found EpMYB2, a typical R2R3-type MYB transcription factor (TF) responsive to methyl jasmonate (MeJA) simulation, is a positive regulator of chicoric acid biosynthesis. In addition to directly regulating chicoric acid biosynthetic genes, EpMYB2 positively regulates genes of the upstream shikimate pathway. We also found that EpMYC2 could activate the expression of EpMYB2 by binding to its G-box site, and the EpMYC2-EpMYB2 module is involved in the MeJA-induced chicoric acid biosynthesis. Overall, we identified an MYB TF that positively regulates the biosynthesis of chicoric acid by activating both primary and specialized metabolic genes. EpMYB2 links the gap between the JA signaling pathway and chicoric acid biosynthesis. This work opens a new direction toward engineering purple coneflower with higher medicinal qualities.

MYB24, MYB144, and MYB168 positively regulate suberin biosynthesis at potato tuber wounds during healing.

The essence of wound healing is the accumulation of suberin at wounds, which is formed by suberin polyphenolic (SPP) and suberin polyaliphatic (SPA). The biosynthesis of SPP and SPA monomers is catalyzed by several enzyme classes related to phenylpropanoid metabolism and fatty acid metabolism, respectively. However, how suberin biosynthesis is regulated at the transcriptional level during potato (Solanum tuberosum) tuber wound healing remains largely unknown. Here, 6 target genes and 15 transcription factors related to suberin biosynthesis in tuber wound healing were identified by RNA-seq technology and qRT-PCR. Dual luciferase and yeast one-hybrid assays showed that StMYB168 activated the target genes StPAL, StOMT, and St4CL in phenylpropanoid metabolism. Meanwhile, StMYB24 and StMYB144 activated the target genes StLTP, StLACS, and StCYP in fatty acid metabolism, and StFHT involved in the assembly of SPP and SPA domains in both native and wound periderms. More importantly, virus-induced gene silencing in S. tuberosum and transient overexpression in Nicotiana benthamiana assays confirmed that StMYB168 regulates the biosynthesis of free phenolic acids, such as ferulic acid. Furthermore, StMYB24/144 regulated the accumulation of suberin monomers, such as ferulates, α, ω-diacids, and ω-hydroxy acids. In conclusion, StMYB24, StMYB144, and StMYB168 have an elaborate division of labor in regulating the synthesis of suberin during tuber wound healing.

NtMYB27 acts downstream of NtBES1 to modulate flavonoids accumulation in response to UV-B radiation in tobacco.

UV-B radiation can induce the accumulation of many secondary metabolites, including flavonoids, in plants to protect them from oxidative damage. BRI1-EMS-SUPPRESSOR1 (BES1) has been shown to mediate the biosynthesis of flavonoids in response to UV-B. However, the detailed mechanism by which it acts still needs to be further elucidated. Here, we revealed that UV-B significantly inhibited the transcription of multiple transcription factor genes in tobacco, including NtMYB27, which was subsequently shown to be a repressor of flavonoids synthesis in tobacco. We further demonstrated that NtBES1 directly binds to the E-box motifs present in the promoter of NtMYB27 to mediate its transcriptional repression upon UV-B exposure. The UV-B-repressed NtMYB27 could bind to the ACCT-containing element (ACE) in the promoters of Nt4CL and NtCHS and served as a modulator that promoted the biosynthesis of lignin and chlorogenic acid (CGA) but inhibited the accumulation of flavonoids in tobacco. The expression of NtMYB27 was also significantly repressed by heat stress, suggesting its putative roles in regulating heat-induced flavonoids accumulation. Taken together, our results revealed the role of NtBES1 and NtMYB27 in regulating the synthesis of flavonoids during the plant response to UV-B radiation in tobacco.

PaMYB11 promotes suberin deposition in Norway spruce embryogenic tissue during cryopreservation: A novel resistance mechanism against osmosis.

The osmotic resistance mechanism has been extensively studied in whole plants or plant tissues. However, little is known about it in embryogenic tissue (ET) which is widely used in plant-based biotechnological systems. Suberin, a cell wall aliphatic and aromatic heteropolymer, plays a critical role in plant cells against osmosis stress. The suberin regulatory biosynthesis has rarely been studied in gymnosperms. Here, PaMYB11, a subgroup 11 R2R3-MYB transcription factor, plays a key role in the osmotic resistance of Norway spruce (Picea abies) ETs during cryoprotectant pretreatment. Thus, RNA-seq, histological, and analytical chemical analyses are performed on the stable transformations of PaMYB11-OE and PaMYB11-SRDX in Norway spruce ETs. DAP-seq, Y1H, and LUC are further combined to explore the PaMYB11 targets. Activation of PaMYB11 is necessary and sufficient for suberin lamellae deposition on Norway spruce embryogenic cell walls, which plays a decisive role in ET survival under osmotic stress. Transcriptome analysis shows that PaMYB11 enhances suberin lamellae monomer synthesis by promoting very long-chain fatty acid (VLCFA) synthesis. PaPOP, PaADH1, and PaTET8L, the first two (PaADH1 and PaPOP, included) involved in VLCFA synthesis, are proved to be the direct targets of PaMYB11. Our study identified a novel osmotic response directed by PaMYB11 in Norway spruce ET, which provides a new understanding of the resistance mechanism against osmosis in gymnosperms.

The MdMYB44-MdTPR1 repressive complex inhibits MdCCD4 and MdCYP97A3 expression through histone deacetylation to regulate carotenoid biosynthesis in apple.

Carotenoids are photosynthetic pigments and antioxidants that contribute to different plant colors. However, the involvement of TOPLESS (TPL/TPR)-mediated histone deacetylation in the modulation of carotenoid biosynthesis through ethylene-responsive element-binding factor-associated amphiphilic repression (EAR)-containing transcription factors (TFs) in apple (Malus domestica Borkh.) is poorly understood. MdMYB44 is a transcriptional repressor that contains an EAR repression motif. In the present study, we used functional analyses and molecular assays to elucidate the molecular mechanisms through which MdMYB44-MdTPR1-mediated histone deacetylation influences carotenoid biosynthesis in apples. We identified two carotenoid biosynthetic genes, MdCCD4 and MdCYP97A3, that were confirmed to be involved in MdMYB44-mediated carotenoid biosynthesis. MdMYB44 enhanced ß-branch carotenoid biosynthesis by repressing MdCCD4 expression, whereas MdMYB44 suppressed lutein level by repressing MdCYP97A3 expression. Moreover, MdMYB44 partially influences carotenoid biosynthesis by interacting with the co-repressor TPR1 through the EAR motif to inhibit MdCCD4 and MdCYP97A3 expression via histone deacetylation. Our findings indicate that the MdTPR1-MdMYB44 repressive cascade regulates carotenoid biosynthesis, providing profound insights into the molecular basis of histone deacetylation-mediated carotenoid biosynthesis in plants. These results also provide evidence that the EAR-harboring TF/TPL repressive complex plays a universal role in histone deacetylation-mediated inhibition of gene expression in various plants.

Seed color patterns in domesticated common bean are regulated by MYB-bHLH-WD40 transcription factors and temperature.

Seed colors and color patterns are critical for the survival of wild plants and the consumer appeal of crops. In common bean, a major global staple, these patterns are also essential in determining market classes, yet the genetic and environmental control of many pigmentation patterns remains unresolved. In this study, we genetically mapped variation for several important seed pattern loci, including T, Bip, phbw, and Z, which co-segregated with candidate genes PvTTG1, PvMYC1, PvTT8, and PvTT2, respectively. Proteins encoded by these genes are predicted to work together in MYB-bHLH-WD40 (MBW) complexes, propagating flavonoid biosynthesis across the seed coat as observed in Arabidopsis. Whole-genome sequencing of 37 accessions identified mutations, including seven unique parallel mutations in T (PvTTG1) and non-synonymous SNPs in highly conserved residues in bipana (PvMYC1) and z (PvTT2). A 612 bp intron deletion in phbw (PvTT8) eliminated motifs conserved since the Papilionoideae origin and corresponded to a 20-fold reduction in transcript abundance. In multi-location field trials of seven varieties with partial seed coat pigmentation patterning, the pigmented seed coat area correlated positively with ambient temperature, with up to 11-fold increases in the pigmented area from the coolest to the warmest environments. In controlled growth chamber conditions, an increase of 4°C was sufficient to cause pigmentation on an average additional 21% of the seed coat area. Our results shed light on key steps of flavonoid biosynthesis in common bean. They will inform breeding efforts for seed coat color/patterning to improve consumer appeal in this nutritious staple crop.

PDR9 allelic variation and MYB63 modulate nutrient-dependent coumarin homeostasis in Arabidopsis.

Plant roots release phytochemicals into the soil environment to influence nutrient availability and uptake. Arabidopsis thaliana roots release phenylpropanoid coumarins in response to iron (Fe) deficiency, likely to enhance Fe uptake and improve plant health. This response requires sufficient phosphorus (P) in the root environment. Nonetheless, the regulatory interplay influencing coumarin production under varying availabilities of Fe and P is not known. Through genome-wide association studies, we have pinpointed the influence of the ABC transporter G family member, PDR9, on coumarin accumulation and trafficking (homeostasis) under combined Fe and P deficiency. We show that genetic variation in the promoter of PDR9 regulates its expression in a manner associated with coumarin production. Furthermore, we find that MYB63 transcription factor controls dedicated coumarin production by regulating both COUMARIN SYNTHASE (COSY) and FERULOYL-CoA 6'-HYDROXYLASE 1 (F6'H1) expression while orchestrating secretion through PDR9 genes under Fe and P combined deficiency. This integrated approach illuminates the intricate connections between nutrient signaling pathways in coumarin response mechanisms.