Investigating the Role of the VAL1 Transcription Factor in Arabidopsis thaliana Embryo Development
Developing oilseeds accumulate oils and seed storage proteins synthesized by the pathways of primary metabolism. Seed development and metabolism are positively regulated at the transcriptional level through the transcription factors belonging to the LAFL regulatory network. The VAL genes encode repressors of the seed maturation program in germinating seeds, but they are also expressed during early stages of seed maturation. VAL1 was identified through a reverse genetics approach as a regulator of seed metabolism, as val1 mutant seeds accumulated elevated levels of storage proteins compared to the wild type. Two VAL1 splice variants were identified, yielding the canonical protein and a truncated protein lacking the plant-homeodomain-like domain important for epigenetic repression. Transcriptomics analysis also revealed that VAL1 is a global epigenetic and transcriptional repressor in developing embryos, though none of the transcripts encoding the LAFL network regulators, including FUSCA3, were affected in val1 embryos. However, VAL1 action is connected specifically to FUSCA3 as 38% of transcripts belonging to the FUSCA3 regulon, but not to other regulons, were largely de-repressed in the absence of VAL1. Based on our model, FUSCA3 activates expression of VAL1 to repress transcription of seed maturation genes without interfering with expression of the core LAFL regulators.