DELAY OF GERMINATION1 requires PP2C phosphatases of the ABA signalling pathway to control seed dormancy

Abstract

The time of seed germination is a major decision point in the life of plants determining future growth and development. This timing is controlled by seed dormancy, which prevents germination under favourable conditions. The plant hormone abscisic acid (ABA) and the protein DELAY OF GERMINATION 1 (DOG1) are essential regulators of dormancy. The function of ABA in dormancy is rather well understood, but the role of DOG1 is still unknown. Here, we describe four phosphatases that interact with DOG1 in seeds. Two of them belong to clade A of type 2C protein phosphatases: ABA-HYPERSENSITIVE GERMINATION 1 (AHG1) and AHG3. These phosphatases have redundant but essential roles in the release of seed dormancy epistatic to DOG1. We propose that the ABA and DOG1 dormancy pathways converge at clade A of type 2C protein phosphatases.

Seed germination and dormancy: The classic story, new puzzles, and evolution

“…The continuous ABA biosynthesis in imbibed seeds, which is catalyzed by the rate‐limiting enzyme NCED (Lefebvre et al ; Millar et al ; Frey et al ), seems to be an essential “final output” of seed dormancy (Nonogaki ). Application of fluridone, a carotenoid biosynthesis inhibitor that averts ABA biosynthesis, releases seed dormancy in most occasions, including the deep dormancy imposed by the DOG1 transgene (Née et al ) ( DOG1 discussed below). Another important output of seed dormancy is the suppression of CYP707A2 , an ABA catabolism gene.…”

“…A breakthrough in seed dormancy research in the past few years is that the biochemical function of DOG1, which was a long‐awaited question, was largely unfolded. Now, it is understood that DOG1 physically interacts with ABA HYPERSENSITIVE GERMINATION1 (AHG1) and AHG3, clade A protein phosphatases 2C (PP2Cs) (Née et al ; Nishimura et al ). AHG1 (Nishimura et al ; Nishimura et al ) and AHG3 (Yoshida et al ) are negative regulators of ABA signaling and seed dormancy.…”

“…AHG1 (Nishimura et al ; Nishimura et al ) and AHG3 (Yoshida et al ) are negative regulators of ABA signaling and seed dormancy. Loss of function mutations in AHG1 ( ahg1‐5 ) or AHG3 ( ahg3‐2 ) enhances seed dormancy, which is intensified in the double mutant ahg1‐5 ahg3‐2 (Née et al ). Similar results were observed also for the ahg1‐1 ahg3‐1 double mutant seeds (Nishimura et al ).…”

“…These results indicate that the two AHG genes act redundantly in the dormancy pathway. When the non‐dormancy mutation dog1‐2 is combined with either of the single ahg mutants, the double mutant seeds ( dog1‐2 ahg1‐5 and dog1‐2 ahg3‐2 ) are completely non‐dormant (Née et al ), which demonstrates the antagonistic role of DOG1 to AHG1 and AHG3 . In contrast, the triple mutant dog1‐2 ahg1‐5 ahg3‐2 seeds are still deeply dormant like the ahg1‐5 ahg3‐2 double mutant (Née et al ), indicating that AHG1 and AHG3 are epistatic to DOG1 .…”

“…When the non‐dormancy mutation dog1‐2 is combined with either of the single ahg mutants, the double mutant seeds ( dog1‐2 ahg1‐5 and dog1‐2 ahg3‐2 ) are completely non‐dormant (Née et al ), which demonstrates the antagonistic role of DOG1 to AHG1 and AHG3 . In contrast, the triple mutant dog1‐2 ahg1‐5 ahg3‐2 seeds are still deeply dormant like the ahg1‐5 ahg3‐2 double mutant (Née et al ), indicating that AHG1 and AHG3 are epistatic to DOG1 . These genetic analyses provide convincing evidence that AHG1 and AHG3 function downstream of DOG1 to promote germination and that DOG1 maintains seed dormancy by sequestering them.…”