Biology subjects

Dubos, C.

Publications and source records attributed to Dubos, C..

3 recordsLinked to original sources

bioRxiv2026

HY5 orchestrates the transcriptional network controlling coumarin-mediated iron acquisition under elevated pH conditions

Iron (Fe) bioavailability is strongly limited in alkaline soils, where reduced Fe solubility severely restricts plant growth and productivity. To overcome this, Arabidopsis thaliana promotes Fe acquisition by secreting Fe-mobilizing coumarins, however, the transcriptional mechanisms coordinating this response is not clearly understood. Here we identify the ELONGATED HYPOCOTYL 5 (HY5), a bZIP transcription factor as a master regulator of coumarin mediated Fe acquisition under alkaline conditions. HY5 positively regulates genes required for coumarin biosynthesis, activation, secretion, and transcriptional control, and loss of HY5 markedly reduces their expression during high-pH-induced Fe deficiency. Chromatin immunoprecipitation analyses revealed that HY5 directly associates with the promoters of these genes, thereby establishing a transcriptional regulatory network that coordinates coumarin biosynthesis. Consistent with this regulatory function, hy5 mutants exhibit reduced coumarin accumulation, impaired root growth, chlorosis, and decreased Fe accumulation under alkaline conditions. Comparable phenotypes in coumarin-hy5 double mutants, together with the restoration of growth by exogenous fraxetin, demonstrate that HY5 functions upstream of coumarin-mediated Fe mobilization. Collectively, our findings identify HY5 as a molecular hub that integrates environmental pH signals with coumarin biosynthesis to promote adaptive Fe acquisition under alkaline conditions, providing a framework for improving crop performance on calcareous soils.

plant biology↗

bioRxiv2026

MYB28 and MYB29 transcription factors regulate iron homeostasis and iron-mobilizing coumarin biosynthesis in Arabidopsis thaliana

Iron (Fe) deficiency is a major constraint for plant growth and triggers extensive physiological and transcriptional reprogramming to maintain Fe homeostasis. Here, we identify the glucosinolate-associated transcription factors MYB28 and MYB29 as previously unrecognized regulators of Arabidopsis thaliana adaptation to Fe deficiency. Across various growth systems, loss of MYB28 increased sensitivity to Fe deficiency, whereas the myb28myb29 double mutant displayed stronger chlorosis, reduced root growth and impaired biomass accumulation, indicating cooperative but unequal functions of these transcription factors. Despite their enhanced Fe-deficiency phenotype, double mutant plants accumulated higher Fe levels in roots and exhibited stronger induction of canonical Fe-deficiency responses, suggesting impaired Fe utilization or distribution rather than defective Fe uptake. RNA-seq revealed extensive transcriptional reprogramming under Fe deficiency, with pronounced deregulation of genes involved in Fe homeostasis, redox processes and growth, particularly in the double mutant. Among these, SCOPOLETIN 8-HYDROXYLASE (S8H) emerged as a major target gene of MYB28. The expression of S8H was almost abolished in myb28 and myb28myb29 mutants, whereas expression of other coumarin biosynthetic genes remained largely unaffected. Promoter activation assays demonstrated that MYB28 activates the S8H promoter, and metabolic analyses showed accumulation of scopolin together with reduced fraxin levels in the mutants, consistent with impaired S8H activity. Collectively, our results identify MYB28 as a key regulator linking specialized metabolism to Fe homeostasis through control of coumarin biosynthesis, thereby expanding the biological functions of MYB28 and MYB29 transcription factors.

plant biology↗

bioRxiv2026

Coumarins link rhizobacteria perception in roots to systemic resistance in leaves

Induced systemic resistance (ISR) is activated in leaves upon root colonization by beneficial microbes, yet the signals linking rhizosphere perception to shoot immunity remain unknown. In the Arabidopsis thaliana-Pseudomonas simiae WCS417 model interaction, the root-specific transcription factor MYB72 and its target gene BGLU42 regulate ISR and the production, activation, and root secretion of coumarins, specialized metabolites involved in plant iron (Fe) acquisition and rhizosphere microbiome assembly. Overexpression of BGLU42 confers constitutive ISR in leaves, suggesting a link between coumarin metabolism and systemic immunity. Here, two-photon multispectral imaging and targeted metabolite profiling revealed that, under Fe-sufficient conditions, WCS417 induces a distinct spatial pattern of F6H1-dependent coumarin accumulation along the root system. These WCS417-induced coumarin signatures differed from those observed under Fe deficiency, indicating activation of a microbiota-specific coumarin metabolic program. Increased coumarin accumulation in roots was followed by a rise in coumarin levels in shoots. Time-resolved transcriptome profiling supported this metabolic reprogramming, showing rapid activation of Fe acquisition and coumarin biosynthesis genes in roots, including F6H1, MYB72, and BGLU42, followed by delayed but similar transcriptional responses in shoots. Functional analyses demonstrated that coumarin biosynthesis is required for WCS417-ISR: the f6h1 mutant failed to mount systemic resistance, whereas F6H1 overexpression conferred constitutive resistance to bacterial and fungal pathogens. In addition, WCS417-mediated coumarin accumulation systemically modulated flg22-triggered reactive oxygen species production in leaves in an F6H1-dependent manner. Together, our results identify coumarins as key mediators linking rhizobacterial perception in roots to systemic immune signaling and resistance in leaves.

plant biology↗