Abstract
The sucrose non-fermenting 1-related protein kinase 2 (SnRK2) family members are plant-specific serine/threonine kinases that are involved in the plant response to abiotic stress and abscisic acid (ABA)-dependent plant development. Further understanding of the evolutionary history and expression characteristics of these genes will help to elucidate the mechanisms of the stress tolerance in Pak-choi, an important green leafy vegetable in China. Thus, we investigated the evolutionary patterns, footprints and conservation of SnRK2 genes in selected plants and later cloned and analyzed SnRK2 genes in Pak-choi. We found that this gene family was preferentially retained in Brassicas after the Brassica-Arabidopsis thaliana split. Next, we cloned and sequenced 13 SnRK2 from both cDNA and DNA libraries of stress-induced Pak-choi, which were under conditions of ABA, salinity, cold, heat, and osmotic treatments. Most of the BcSnRK2s have eight exons and could be divided into three groups. The subcellular localization predictions suggested that the putative BcSnRK2 proteins were enriched in the nucleus. The results of an analysis of the expression patterns of the BcSnRK2 genes showed that BcSnRK2 group III genes were robustly induced by ABA treatments. Most of the BcSnRK2 genes were activated by low temperature, and the BcSnRK2.6 genes responded to both ABA and low temperature. In fact, most of the BcSnRK2 genes showed positive or negative regulation under ABA and low temperature treatments, suggesting that they may be global regulators that function at the intersection of multiple signaling pathways to play important roles in Pak-choi stress responses.
Highlights
In nature, plants are frequently exposed to harmful environmental conditions, such as low or high temperature, high salinity, and drought
With the exception of SmoSnRK2s and PpaSnRK2s all of the genes in the tree clustered into group III, and the sucrose non-fermenting 1-related protein kinase 2 (SnRK2) genes in C. reinhardtii, P. patens, and S. moellendorffii were homologous to SnRK2.6, suggesting that the SnRK2.6 and group III genes were the most ancient gene and group, respectively, among the SnRK2 genes
The expansion of group I played a major role in the expansion of the SnRK2 gene family
Summary
Plants are frequently exposed to harmful environmental conditions, such as low or high temperature, high salinity, and drought. The SnRK2.2/2.3/2.6 triple-mutant plants are nearly completely insensitive to ABA, which was used to establish the role of ABA dependent SnRK2s in the plant response to water deficit, seed maturation, and germination. These reports indicate that SnRK2.2/3/6 function as primary positive regulators, and suggest that ABA signaling is controlled by the dual modulation of SnRK2.2/3/6 and groupA PP2Cs (Fujii and Zhu, 2009; Fujii et al, 2009; Nakashima et al, 2009). In 2013, SnRK2 protein kinase substrates were identified by Zhu’s laboratory (Wang et al, 2013), including proteins involved in flowering time regulation, RNA and DNA binding, miRNA and epigenetic regulation, signal transduction, chloroplast function, and many other cellular processes. This work significantly contributed to the understanding of the role of SnRK2 protein kinases and the downstream effectors of ABA action
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