Transcriptional regulation of transcription factor genes WRI1 and LAFL during Brassica napus seed development.

The WRINKLED1 (WRI1) and LAFL (LEAFY COTYLEDON1 [LEC1], ABSCISIC ACID INSENSITIVE3 [ABI3], FUSCA3 [FUS3], and LEC2) transcription factors play essential roles in governing seed development and oil biosynthesis. To gain a comprehensive understanding of the transcriptional regulation of WRI1 and LAFL, we conducted genome-wide association studies for the expression profiles of WRI1 and LAFL in developing seeds at 20 and 40 days after flowering (DAF) using 302 rapeseed (Brassica napus) accessions. We identified a total of 237 expression quantitative trait nucleotides (eQTNs) and 51 expression QTN-by-environment interactions (eQEIs) associated with WRI1 and LAFL. Around these eQTNs and eQEIs, we pinpointed 41 and 8 candidate genes with known transcriptional regulations or protein interactions with their expression traits, respectively. Based on RNA-sequencing and assay for transposase-accessible chromatin with high-throughput sequencing data, we employed the Extreme Gradient Boosting and Basenji models which predicted 15 candidate genes potentially regulating the expression of WRI1 and LAFL. We further validated the predictions via tissue expression profile, haplotype analysis, and expression correlation analysis and verified the transcriptional activation activity of BnaC03.MYB56 (R2R3-MYB transcription factor 56) on the expression of BnaA09.LEC1 by dual-luciferase reporter and yeast 1-hybrid assays. BnaA10.AGL15 (AGAMOUS-LIKE 15), BnaC04.VAL1 (VIVIPAROUS1/ABSCISIC ACID INSENSITIVE3-LIKE 1), BnaC03.MYB56, and BnaA10.MYB56 were coexpressed with WRI1 and LAFL at 20 DAF in M35, a key module for seed development and oil biosynthesis. We further validated the positive regulation of MYB56 on seed oil accumulation using Arabidopsis (Arabidopsis thaliana) mutants. This study not only delivers a framework for future eQEI identification but also offers insights into the developmental regulation of seed oil accumulation.