Abscisic acid regulates iron accumulation in plant seeds via the PYLs-bHLH IVc-YSLs module.

Abstract

Abscisic acid (ABA) is pivotal in seed development, yet its role in iron (Fe) homeostasis remains unclear. Here, we reveal a PYLs-bHLH IVc-YSLs module that mediates ABA-dependent suppression of seed Fe accumulation in <i>Arabidopsis</i>. During seed maturation, ABA receptors PYLs directly interact with bHLH34/104/115 transcription factors, blocking their binding to <i>YSL1/3</i> promoters to inhibit Fe transport. Conversely, Fe deficiency triggers bHLH104/115 to repress <i>ABA2</i>, reducing ABA biosynthesis and <i>PYL</i> expression to derepress <i>YSL1/3</i> expression-a feedback loop balancing Fe and ABA levels. Genetic analyses confirm that this module governs Fe loading, as ABA-deficient mutants (<i>aba2-1</i>, <i>nced6-1</i>) and <i>pyr1 pyl124</i> quadruple mutants accumulate higher Fe, while <i>bhlh34 104 115</i> phenocopies <i>ysl1 ysl3</i> Fe deficiency. Our findings establish ABA as a dual regulator that safeguards Fe homeostasis by preventing toxicity during maturation while enabling adaptive Fe storage under deficiency. This mechanistic insight opens avenues for bioengineering crops with enhanced seed Fe content, addressing global nutritional challenges.