Cloning and molecular characterization of five MAPKK genes from grapevine (Vitis vinifera) and two of them positively regulate salt and drought tolerance in transgenic Arabidopsis
Abstract Background: The mitogen-activated protein kinase (MAPK) cascade plays an important role in plant development and stress response. In particular, MAPK kinases (MAPKKs/MKKs) have been reported to play a crucial role in MAPK cascades that mediate a variety of stress responses in plants. Few MKKs in grapevine (Vitis vinifera), however, have been functionally characterized.Results: In the present study, five MKK members in grapevine (‘Pinot Noir’) were identified, cloned and designated as VvMKK1-VvMKK5. A phylogenetic analysis grouped these into four sub-families based on the similarity of their conserved motifs and gene structure to other Arabidopsis MKK members. RT-qPCR results indicated that the expression of VvMKK1, VvMKK2, VvMKK4, and VvMKK5 was up-regulated in mature leaves, young leaves, and roots, but exhibited low expression levels in leaf petioles. VvMKK2, VvMKK3, and VvMKK5 genes were differentially up-regulated when grapevine leaves were inoculated with spores of Erisyphe necator, or treated with SA, ETH, H2O2, or exposed to drought, indicating that these genes may be involved in a variety of signaling pathways. Over expression of VvMKK2 and VvMKK4 genes in transgenic Arabidopsis plants resulted in the production of seeds with a significantly higher germination and survival rate, and better seedling growth under stress conditions than wild-type plants. Overexpression of VvMKK2 in Arabidopsis resulted in improved salt and drought stress tolerance while overexpression of VvMKK4 improved salt stress tolerance.Conclusions: Results of the present investigation provide a better understanding of the interaction and function of MAPKKK-MAPKK-MAPK genes at the transcriptional level in grapevine and led to the identification of candidate genes for improved drought and salt stress in grapes.