Abstract
Seed dormancy is a poorly understood process. To identify molecular components that regulate seed dormancy, we screened T-DNA insertion lines and identified a mutant designated honsu (hon). HON loss-of-function mutants display deep seed dormancy, whereas HON-overexpressing lines display shallow seed dormancy. HON encodes a seed-specific group A phosphatase 2C (PP2C) and is the major negative regulator of seed dormancy among group A PP2Cs. Like other PP2C family members, HON interacts with PYR1/RCAR11 in the presence of abscisic acid (ABA). Our analysis indicates that HON inhibits ABA signaling and activates gibberellin (GA) signaling, and both of these conditions must be satisfied to promote the release of seed dormancy. However, activation of GA signaling by HON is an indirect effect attributable to weakened ABA signaling. HON mRNA levels are increased in mutants displaying shallow seed dormancy or under conditions that promote the release of seed dormancy, and decreased in mutants displaying deep seed dormancy or under conditions that deepen seed dormancy. Taken together, our results indicate that seeds homeostatically regulate dormancy by adjusting the level of HON.
