A Study on the Genes Related with Seed Dormancy in Arabidopsis thaliana

Abstract

Seed dormancy is a phenomenon that seed postpones its growth until environment is suitable for its survival. Some genetic or environmental factors that affect seed dormancy have been identified but the mechanism of controlling seed dormancy is still elusive. Recently, some epigenetic regulators of seed dormancy have been reported. AtJmj4, a gene encoding H3K4 demethylase in Arabidopsis, is expressed highly in seed of freshly-harvested (FH) state which possesses the highest seed dormancy level. This suggests that AtJmj4 might play a role in the regulation of seed dormancy. Meanwhile, OsSDR4 is well known as a seed dormancy regulator in rice. Several homologs of OsSDR4 in Arabidopsis have been discovered depending on their amino acid sequence homologies

AtSDR4 is the closest homolog of OsSDR4. The lack of AtSDR4 caused enhanced seed dormancy, which is the opposite phenotype of ossdr4 mutation, which causes a reduced seed dormancy. The function of other homologs, AtSDR4H1 and AtSDR4H2, in seed dormancy has also not been reported. In this study, AtJmj4 and AtSDR4 were investigated at the aspect of seed dormancy regulation. The atjmj4-1 mutation did not alter the seed dormancy phenotype in wild-type (WT) Columbia (Col) background or ColDOG1_Cvi backgrounds at 22 ℃. However, atjmj4-1 seeds showed reduced dormancy than WT seeds at 12 ℃. In the dormancy test using atsdr4-1, atsdr4h1-1, atsdr4h2-1, and their multiple mutants, it was suggested that atsdr4-1 but not atsdr4h1-1 or atsdr4h2-1 mutation enhances the seed dormancy. Gene expression analysis revealed that the genes involved in ABA synthesis and signaling, as well as DOG1, the representative seed dormancy regulator, are upregulated in atsdr4-1 FH seeds than in WT seeds. To test if any phenotypes related to germination also exist, red light-dependent germination tests were performed and none of atjmj4-1, atsdr4-1, atsdr4h1-1 and atsdr4h2-1 showed substantially altered germination phenotypes, although atsdr4-1 showed retarded radicle-emergence phenotype. Germination tests with exogenously supplied ABA suggested that the slow radicle extrusion phenotype of atsdr4-1 is probably due to the ABA hypersensitivity. Overall, these results indicate that AtJmj4 is a minor positive regulator of seed dormancy at low temperature and AtSDR4 is a major negative regulator of seed dormancy.