HSI2/VAL1 Silences to Regulate the Developmental Transition from Seed Maturation to Vegetative Growth in Arabidopsis.

Gene expression during seed development in is controlled by transcription factors including LEAFY COTYLEDON1 (LEC1) and LEC2, ABA INSENSITIVE3 (ABI3), FUSCA3 (FUS3), known as LAFL proteins, and AGAMOUS-LIKE15 (AGL15). The transition from seed maturation to germination and seedling growth requires the transcriptional silencing of these seed maturation-specific factors leading to downregulation of structural genes including those that encode seed storage proteins, oleosins, and dehydrins. During seed germination and vegetative growth, B3-domain protein HSI2/VAL1 is required for the transcriptional silencing of genes. Here, we report chromatin immunoprecipitation analysis indicating that HSI2/VAL1 binds to the upstream sequences of the gene but not at , , , or loci. Functional analysis indicates that the HSI2/VAL1 B3 domain interacts with two RY elements upstream of the coding region and at least one of them is required for HSI2/VAL1-dependent repression. Expression analysis of the major seed maturation regulatory genes , , , and in different genetic backgrounds demonstrates that HSI2/VAL1 is epistatic to and represses the seed maturation regulatory program through downregulation of by deposition of H3K27me3 at this locus. This hypothesis is further supported by results that show that HSI2/VAL1 physically interacts with the Polycomb Repressive Complex 2 component protein MSI1, which is also enriched at the locus.