The bHLH112-ATML1 transcriptional module represses oil accumulation in seeds

Seed oil accumulation is orchestrated by complicated multi-level networks, with transcriptional regulation playing pivotal roles in this process. However, the mechanism underlying how transcription factors (TFs) and their regulatory network regulate oil accumulation in seeds is not completely understood to date. In this study, we identified two TFs, basic helix-loop-helix112 (bHLH112) and ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1), which are highly expressed in developing embryos and act as key repressors of oil accumulation in seeds. We further showed that bHLH112 directly inhibits the expression of WRINKLED1, PYRUVATE DEHYDROGENASE E1 BETA1 (PDH-E1β1), and SUPPRESSOR OF SA INSENSITIVE2, while ATML1 directly inhibits LEAFY COTYLEDON1, ABSCISIC ACID INSENSITIVE3, PDH-E1β1, and FATTY ACID ELONGATION1 during seed maturation. We demonstrated that bHLH112 and ATML1 physically interact and function additively to suppress seed oil production. Further analyses revealed that their synergistic repressive action on seed oil deposition is partially mediated through the common direct target PDH-E1β1, a positive regulator of oil biosynthesis. Together, our work identifies a bHLH112-ATML1 transcriptional module that fine-tunes seed oil accumulation, thereby providing insights into the underlying regulatory network and highlighting promising genetic targets for oil enhancement in seeds of oil-producing crops.