Isolation and functional characterization of W55a encoding a putative SnRK2 protein in wheat Running title: A wheat SnRK2 kinase mediates multiple stress responses

Protein kinases play crucial roles in response to external environment stress signals. A putative protein kinase, W55a, belonging to SNF1-related protein kinase 2 (SnRK2) subfamily, was isolated from a cDNA library of drought-treated wheat seedlings. The entire length of W55a was obtained using rapid amplification of 5’ cDNA ends (5’-RACE) and reverse transcription-PCR (RT-PCR). It contains a 1,029 bp open reading frame (ORF) encoding 342 amino acids. The deduced amino acid sequence of W55a had eleven conserved catalytic subdomains and one Ser/Thr protein kinase active-site that characterize Ser/Thr protein kinases. Phylogenetic analysis showed that W55a was 90.38% homologous with rice SAPK1, a member of the SnRK2 family. Using nullisomic-tetrasomic and ditelocentric lines of Chinese Spring, W55a was located on chromosome 2BS. Expression pattern analysis revealed that W55a was upregulated by drought and salt, exogenous abscisic acid, salicylic acid, ethylene and methyl jasmonate, but was not responsive to cold stress. In addition, W55a transcripts were abundant in leaves, but not in roots or stems, under environmental stresses. Transgenic Arabidopsis plants overexpressing W55a exhibited higher tolerance to drought. Based on these findings, W55a encodes a novel dehydration-responsive protein kinase that is involved in multiple stress signal transduction.