Abstract: Phosphorylation of protein kinases has profound effects on their activity and interaction with other proteins. Tyrosine phosphorylation was reported to be involved in various physiological processes in plants; however, no typical receptor tyrosine kinase has been isolated from plants thus far. Dual-specificity kinases are potentially responsible for the phosphorylation of both tyrosine and serine/threonine of target proteins. A cDNA clone encoding a putative dual-specificity protein kinase was isolated by screening the cDNA GAL4 activation domain (AD) fusion library of soybean (Glycine max L.), and its entire length was obtained using 5''-rapid amplification of cDNA ends. The predicted polypeptide of 330 amino acid residues, designated as GmSTY1, contains all 11 conserved subdomains, which share common characteristics with both the serine/threonine and tyrosine protein kinases reported thus far. In addition, three potential N-linked glycosylation sites (NXS/T), as well as phosphorylation motifs (SXXXS/T), were observed, suggesting that GmSTY1 may be post-translationally modified. Furthermore, a potential N-myristoylation motif (MGARCSK) was found, suggesting that the GmSTY1 protein could associate with membranes in vivo. Southern blotting analysis revealed a single-copy of GmSTY1 in the genome. Northern blotting analysis showed that this gene was upregulated by drought and salt treatment in a time-dependent manner; however, exogenous abscisic acid (ABA) could not significantly affect the mRNA accumulation of GmSTY1. Interestingly, the transcript of this gene was remarkably downregulated by cold treatment during the early stages of the response, but upregulated later. These results indicate that the protein kinase was possibly regulated by abiotic stresses in an ABA-independent pathway.(Author for correspondence.Tel: 010 6891 8789; E-mail: mayzh@mail.caas.net.cn)

Key words: abiotic stress, dual-specificity, Glycine max, serine/threonine/tyrosine protein kinase.