Rice SERK1 gene positively regulates somatic embryogenesis of cultured cell and host defense response against fungal infection

Here we report on the isolation and characterization of a somatic embryogenesis receptor-like kinase (OsSERK1) gene in rice (Oryza sativa). The OsSERK1 gene belongs to a small subfamily of receptor-like kinase genes in rice and shares a highly conserved gene structure and extensive sequence homology with previously reported plant SERK genes. Though it has a basal level of expression in various rice organs/tissues, as high expression level was detected in rice callus during somatic embryogenesis. Suppression of OsSERK1 expression in transgenic calli by RNA interference resulted in a significant reduction of shoot regeneration rate (from 72% to 14% in the japonica rice Zhonghua11). Overexpression of OsSERK1, however, increased the shoot regeneration rate (from 72% to 86%). Interestingly, OsSERK1 is significantly activated by the rice blast fungus, particularly during the incompatible interaction, and is associated with host cell death in Sekigushi lesion mimic mutants. This gene is also inducible by defense signaling molecules such as salicylic acid, jasmonic acid, and abscisic acid. Furthermore, constitutive overexpression of OsSERK1 in two rice cultivars led to an increase in host resistance to the blast fungus. Our data suggest that OsSERK1 may partially mediate defense signal transduction in addition to its basic role in somatic embryogenesis.