Bat1Is Involved In The Repression Of ABA Synthesis And Starch Accumulation In Arabidopsis

Starch is one of the major carbon resources for plants utilization and human consumption. Increasing evidence shows that starch deposition is correlated with hormone signaling. Yet, how starch accumulation is regulated in response to plant hormones remains largely unknown. BR-related acyltransferase1(BAT1), a gene encoding a putative acyltransferase, has recently been reported to maintain endogenous brassinosteroids (BRs) levels by acylating brassinolide intermediates. Here, we show that BAT1negatively regulates leaf starch deposition by reducing endogenous ABA levels. Microarray data indicates that the expression of genes involved in multiple material metabolic and energy metabolic pathways was downregulated in BAT1-overexpression (BAT1-OX) lines, suggesting an impaired primary metabolic system in BAT1-OX lines. The starch content was decreased in BAT1-OX leaves and opposite result was observed in BAT1knockout (bat1-1) and RNAi (BAT1-RNAi) plants compared with wild types. Consistent with the alteration in starch contents, ABA levels were decreased in BAT1-OX lines, whereas they were elevated in BAT1-deficient lines, compared with wild types. Furthermore, exogenous ABA was able to induce starch accumulation in wild type Arabidopsis leaves and ectopic starch accumulation was rescued by exogenous application of ABA synthesis inhibitor (fluridone, FLU) in BAT1-deficient lines, implying the important role of ABA in the induction of excessive starch deposition. Together, our results substantiate that ABA signaling and starch deposition are interconnected and BAT1functions as a negative regulator of ABA synthesis and the subsequent suppression of starch accumulation.