Overexpression of tomato SpMPK3 gene in Arabidopsis enhances the osmotic tolerance

Mitogen-activated protein kinase (MAPK) class plays diverse roles in plant response to abiotic stresses. SpMPK3, a serine/threonine protein kinase containing a Thr-Glu-Tyr (TEY) activation domain, has been reported to function against bacterial, fungus and insect attack in tomatoes. But, its roles in abiotic stress response are poorly experienced. Herein, the experiment we have conducted demonstrates that there is a substantial increase of SpMPK3 expression in tomato leaves by drought, salt and cold stress. Transgenic Arabidopsis plants overexpressing SpMPK3 showed improved seed germination and antioxidant capacity under osmotic stress, but decreased seed germination with ABA treatment compared to wile-type. In addition, SpMPK3 overexpression enhanced the transcription levels of ABA inducible genes-RD29A, RAB18 and RD22, and transcription factor genes-ZAT6, ZAT10 and MYB44, in transgenic Arabidopsis compared with wild-type in response to ABA or salt stress. These results suggest that SpMPK3 is a positive regulator in response to osmotic stress in Arabidopsis at germination and development stage.