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. 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.
A. Marín-Peña, Inmaculada Coleto, José Alberto Urbano-Gámez et al.· bioRxiv· 0 citations
Fruit metabolism is highly sensitive to environmental variations, with climate change disrupting processes that determine fruit composition and quality. In grapes, elevated temperatures increase sugar accumulation but reduce anthocyanin levels as co-occurring responses under heat stress, leading to imbalances that affect wine typicality. To explore sugar signaling and its interaction with abscisic acid (ABA) in regulating anthocyanin biosynthesis, we conducted a comprehensive transcriptomic and phenotypic analysis using a “Gamay Fréaux” (GT) cell suspension model. Treatments included ABA combined with varying glucose concentrations, glucose analogs, and hexokinase inhibitors. High glucose levels increased anthocyanin concentration by 13.2% compared to low glucose levels, whereas exogenous ABA induced far stronger increases of 108.4% and 94.4% under low- and high-glucose conditions, respectively, relative to ABA-free controls. Additionally, mannose contributed to sugar signaling, with sugar-induced anthocyanin accumulation dependent on hexokinase-mediated phosphorylation. Transcriptomic analysis revealed that while ABA strongly upregulated anthocyanin biosynthetic genes, the effect of glucose on these genes was modest. Notably, 3OM treatment induced upregulation of several structural genes but resulted in reduced anthocyanin accumulation, suggesting regulation primarily through post-transcriptional mechanisms and additional factors influencing post-translational control. By developing an open-source GT-transcriptome analysis tool and integrating it with anthocyanin quantification, we identified VviCIPK25 as a candidate gene whose expression correlates with anthocyanin accumulation in response ABA, and which may respond indirectly to sugar-induced phosphorylation status. This study provides a comprehensive transcriptomic resource for understanding anthocyanin regulation in grape cell suspensions and identifies VviCIPK25 as a candidate gene for future functional studies. Our findings also highlight the importance of post-transcriptional regulation in anthocyanin biosynthesis, as transcriptional changes do not always predict phenotypic outcomes.
