Genome-Wide Profiling of Soybean WRINKLED1 Transcription Factor Binding Sites Provides Insight into the Regulation of Fatty Acid and Triacylglycerol Biosynthesis Program in Seeds

Abstract Understanding the regulatory mechanisms controlling storage lipid accumulation will inform strategies to enhance seed oil quality and quantity in crop plants. The WRINKLED1 transcription factor (WRI1 TF) is a central regulator of lipid biosynthesis. We characterized the genome-wide binding profile of soybean (Gm)WRI1 and show that the TF directly regulates genes encoding numerous enzymes and proteins in the fatty acid and triacylglycerol biosynthetic pathways. GmWRI1 binds primarily to regions downstream of target gene transcription start sites. We showed that GmWRI1 bound regions are enriched for the canonical WRI1 DNA binding element, the AW Box (CNTNGNNNNNNNCG), and another DNA motif, the CNC Box (CNCCNCC). Functional assays showed that both DNA elements mediate transcriptional activation by GmWRI1. We also show that GmWRI1 works in concert with other TFs to establish a regulatory state that promotes fatty acid and triacylglycerol biosynthesis. In particular, comparison of genes targeted directly by GmWRI1 and by GmLEC1, a central regulator of the maturation phase of seed development, reveals that the two TFs act in a positive feedback subcircuit to control fatty acid and triacylglycerol biosynthesis. Together, our results provide new insights into the genetic circuitry in which GmWRI1 participates to regulate storage lipid accumulation during seed development. Significance Statement We report the genome-wide profiling of DNA sequences bound by and the genes directly- regulated by soybean WRINKLED1, a central regulator of storage lipid accumulation in oilseed plants. The information offers new insights into the mechanisms by which WRINKLED1 regulates genes encoding lipid biosynthetic enzymes and establishes a regulatory environment that promotes oil accumulation, and it may aid in the design of strategy to alter storage lipid accumulation in oilseeds.