PDC1 is activated by ABF4 and inhibits seed germination by promoting ROS accumulation in Arabidopsis

Abstract

Seed germination is tightly regulated by multiple endogenous signaling molecules and metabolites, such as abscisic acid (ABA), the products of fatty acid β-oxidation for energy production and reactive oxygen species (ROS). In Arabidopsis the expression of pyruvate decarboxylase 1 (PDC1), which is involved in fermentation metabolism, was strongly induced by ABA during seed germination, suggesting that PDC1 might regulate seed germination in response to ABA. To prove this hypothesis, we characterized the role of PDC1 in ABA-mediated inhibition of seed germination. The percentages of seed germination and cotyledon greening of PDC1-deficiency pdc1 mutants were higher, whereas those of PDC1-overexpression lines were lower, than those of wild-type (WT) plants in the presence of ABA. Chromatin immunoprecipitation and electrophoretic mobility shift assays indicated that the ABA-responsive element BINDING FACTOR 4 (ABF4) transcription factor could bind to the PDC1 promoter and activate gene expression. ABA-induction of PDC1 expression was impaired in abf4–1 mutants, and overexpression of ABF4 in pdc1–1 plants can partially rescue their ABA-insensitive phenotypes. In addition, ABA-induced ROS accumulation was impaired in pdc1–1 seedlings, whereas it was enhanced in PDC1-overexpression lines, as compared with WT plants. Furthermore, the levels of free fatty acids were lower in pdc1–1 mutants, but higher in the PDC1-overexpression lines, than WT plants. This is consistent with the altered expression of fatty acid β-oxidation-related genes in these plants. Taken together, our results indicated that ABF4 activates PDC1 expression, thereby promoting fatty acid β-oxidation and enhancing ROS accumulation, leading to inhibition of seed germination in Arabidopsis.