SCL15 Regulates the Release of Seed Dormancy in Arabidopsis thaliana by Integrating the Circadian Clock, Hormonal Signals and Cell Wall Remodelling.

Dormancy release and germination of the seed are two separate, but continuous phases controlled by both external (e.g., light and temperature) and internal (e.g., circadian clock and hormones) cues. In eudicot seeds, the endosperm tissues play a key role in dormancy release and germination through dynamic modulation of wall components and biomechanics. However, the mode of action by which the circadian oscillator influences dormancy release by modulation of endosperm wall biomechanics remains elusive. SCARECROW-LIKE15 (SCL15) represses embryonic gene expression in seedlings through interaction with HISTONE DEACETYLASE19 (HDA19) in Arabidopsis thaliana. Here, we report that SCL15 plays a positive role in primary dormancy release, which is associated with gene expression changes in circadian, abscisic acid, auxin and cell wall (CW) remodelling pathways, based on studies using SCL15 mutant and Napin promoter-driven SCL15 expression lines. SCL15 was found to affect the expression of genes whose products modify endosperm wall biomechanical features, possibly through regulation of local auxin accumulation and evening-phased clock components. RNA-seq analysis supported the notion that dormancy release is associated with changes in the expression of genes associated with circadian and hormone-mediated pathways, which in turn affect CW structure.