Abstract
Although plant MAPK cascades play decisive roles in stress responses, their contribution in wheat remains largely unknown. The bread wheat TMPK3 (wheat Mitogen Activated Protein Kinase) was previously recognized as a serine/threonine protein kinase carrying a Thr-Glu-Tyr (TEY) activation domain, but its functional role in environmental stress response is insufficiently studied. Here in, we showed that TMPK3 is auto-phosphorylated in vitro and can be phosphorylated by the constitutively active Arabidopsis AtMKK2. TMPK3 was also capable to phosphorylate its substrate, the MAP kinase phosphatase 1. Moreover, we investigated the involvement of TMPK3 in plant tolerance to salt/osmotic stresses. Our results show that TMPK3 complements the salt sensitivity of the Arabidopsis loss-of-function mpk3-1 mutant, where its overexpression promotes salt and osmotic stress tolerance to levels exceeding those observed in wild type plants. This tolerance is associated to a lower sensitivity to exogenous ABA, and increased stronger accumulation of proline contents, higher survival, and lower water loss rates as well as attenuated oxidative stress status. In summary, our data provide evidence that TMPK3 plays a positive role in salt and drought stress responses in plants.