Genome-Wide Phylogenetic Analysis of Stress-Activated Protein Kinase Genes in Rice (OsSAPKs) and Expression Profiling in Response to Xanthomonas oryzae pv. oryzicola Infection

All members of the SnRK2 protein kinase gene family encoded by the rice (Oryza sativa L.) genome are activated by hyperosmotic stress, and have been designated as stress-activated protein kinases (SAPKs). In this study, gene structures, phylogeny, and conserved motifs for the entire OsSAPK gene family in rice have been analyzed. Moreover, expression patterns of OsSAPK in response to infection with Xanthomonas oryzae pv. oryzicola (Xoc) were investigated. A total of ten OsSAPK genes in the japonica rice cultivar 9804 were identified and classified into four groups. All genes had similar exon–intron structures and organization of putative motifs/domains, and shared the same four motifs (motifs 1–4). Group I (OsSAPK1 and OsSAPK2) shared another two motifs (motif 5 and motif 10), while group III (OsSAPK8, OsSAPK9 and OsSAPK10) had seven motifs in common (motifs 1–7). Moreover, we found that four OsSAPKs, including OsSAPK3, OsSAPK5, OsSAPK7 and OsSAPK9, were significantly upregulated in response to infection by Xoc in rice plants carrying the nonhost resistance gene Rxo1. Four of the OsSAPK genes in which expression was upregulated were localized to both the cytoplasm and nucleus, but clustered in different groups, suggesting that they are involved in different resistance signal transduction pathways. These results will provide useful information for the future functional dissection of this gene family.