The epigenetic regulation of the master stomatal regulator speechless by the arabidopsis val family of transcriptional repressors
L. C. CHUA1, and O. S. LAU1,*

1Department of Biological Sciences, National University of Singapore, Singapore, 117558, Singapore.

Stomata are epidermal microscopic pores that facilitate gas exchange between plants and the environment. The initiation and maintenance of the stomatal cell fate requires a basic helix-loop-helix transcription factor SPEECHLESS (SPCH) that programs the stem cell-like stage by controlling the expression of downstream genes. However, how the epigenetic status of SPCH is modulated during development is largely unknown. The VIVIPAROUS1/ABI3-LIKE (VAL) family of proteins are transcriptional repressors that were previously demonstrated as sequence-specific cis-regulatory DNA readers, and they epigenetically regulate the expression of target genes by recruiting the highly conserved Polycomb group proteins. Here I show that the T-DNA insertional val loss-of-function mutants displayed higher stomatal density in both the hypocotyl and cotyledons, with upregulated transcript levels of SPCH and other key stomatal regulators. Moreover, yeast one-hybrid and in vitro DNA-protein pull-down assays demonstrated the positive interaction between VALs and SPCH promoter through sequence-specific binding, suggesting that VALs could act as upstream regulators of SPCH. I further show that the tissue-specific overexpression of VALs suppressed the development of stomata and caused diverted fates of stomatal lineage cells, which are indicative of mis-regulated SPCH expression. Further experiments are ongoing to elucidate the molecular mechanism by which the VALs regulate stomatal development.