AtSERK1 and BAK1/AtSERK3 positively regulate seed germination in response to saline condition in Arabidopsis

Salt stress adversely affects plants by inhibiting seed germination, growth, and development throughout their life cycle. Abscisic acid (ABA) is a primary plant hormone that regulates seed dormancy under environmental stresses. The salt-overly sensitive (SOS) pathway regulates ion homeostasis in seedlings grown under saline conditions. Recently, sos mutants have been reported to exhibit higher seed germination rates than wild-type plants under salt conditions. Previously, BRI1-associated receptor kinase 1 (BAK1) was demonstrated to be involved in ABA-induced stomatal closure under drought conditions. In the present study, we demonstrated that bak1 and atserk1 mutants exhibited stronger inhibition of seed germination on salt-containing media than wild-type plants, and the degree of inhibition was greater in atserk1 mutants. However, seedling growth after germination was not different among the genotypes. RNA-sequencing analysis of salt-treated atserk1 seeds revealed that the number of differentially expressed genes (DEGs) induced by salt stress was lower in atserk1 than in wild-type plants. However, most DEGs in atserek1 were involved in signal transduction with phosphorelay events, suggesting that AtSERKs may function post-transcriptionally to regulate seed germination. Furthermore, bak1/sos2 or atserk1/sos2 double mutant analyses showed that AtSERKs act downstream of SOS2 in the salt-induced inhibition of seed germination. Taken together, these results suggest that both AtSERKs and SOS proteins work together to regulate the balance between seed germination and maintenance of seed dormancy under saline conditions.