| Drought is one of the most important abiotic constraints limiting the yield of wheat. Mining and utilizing the genes involved in drought tolerance in plants are of significance not only on further understanding the molecular mechanism of drought tolerance, but also on improving the drought tolerance of crops via genetic engineering.Protein phosphorylation/dephosphorylation is major signaling events induced by abiotic stresses in higher plants. Sucrose nonfermenting 1-related protein kinase 2 (SnRK2), belonging to serine-threonine protein kinase, plays an important role in the process of sugar signal transduction. It is reported that the gene family is activated by hyperosmotic stress and relays the stress signal via phosphorylation. TaPK7 is a member of SnRK2 gene family of wheat.In the study, we isolated TaPK7 from wheat, and performed functional analysis and the single nucleotide polymorphism (SNP) identification. The results are as following:1. TaPK7 was isolated from wheat by in silico cloning and RT-PCR, which contains an open reading frame of 1074 bp, encodes a protein of 357 amino acids with a calculated molecular mass of 42 kD and isoelectric point (pi) of 5.47. Sequence analysis indicated this putative protein possessed both activities of the serine/threonine and tyrosine kinases. Phylogenetic analysis results showed that TaPK7 was high homologous to the orthologous genes from rice. Real-time quantitative PCR results revealed that TaPK7 was obviously responsive to the four abiotic stresses, but with significant different expression patterns. The sensitivity of TaPK7 responding to stresses was in the order of high salinity > hyperosmolality > low temperature (4℃) > abscisic acid. Subcellular localization revealed that TaPK7 dispersed in cytoplasm, as well as on nucleus and plasma membrane.2. Function analysis revealed that homozygous transgenic Arabidopsis plants displayed more tolerance to different abiotic stresses than the wild type, including drought, salt and low temperature.3. The genomic size of TaPK7 was about 4.5 kb, which contained 9 extrons and 8 introns. Fifty accessions of different genotypes for drought tolerance, including 45 hexaploid wheat accessions and 5 diploid species of wheat relatives, were used to detect the single nucleotide polymorphisms of TaPK7. Sixty four SNP and nine InDel were detected in a total of 220448 bp nucleotide acids, and the frequencies of SNP and InDel were 1 SNP /3445 bp and 1 InDel /24494 bp, respectively. The nucleotide diversity value in non-coding region was higher than that in coding region, which suggested that the coding region suffered stronger selection pressure than non-coding region. Ka/Ks value of TaPK7 was 0.415, which indicated that TaPK7 was a conservative gene. Sixteen SNPs were observed in coding region, and most of them happed in drought-tolerant accessions. A total of 21 haplotypes were identified from the plant materials. Among them, 7 haplotypes of TaPK7 were only related to accessions with drought-tolerant or drought-sensitive characteristics, 11 haplotype contained medium-drought-tolerant accessions, but 3 haplotypes contained both types of accessions. SNPs in TaPK7 were correlative with drought tolerance, but it couldn't explain the mechanism of drought tolerance completely in wheat.All these results demonstrated that TaPK7 plays an important role in plant for drought response.
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