Date Published: February 21, 2018
Publisher: Public Library of Science
Author(s): Youjing Wang, Lin Jiang, Jiaqi Chen, Lei Tao, Yimin An, Hongsheng Cai, Changhong Guo, Keqiang Wu.
The WRKY transcription factors play an important role in the regulation of transcriptional reprogramming associated with plant abiotic stress responses. In this study, the WRKY transcription factor MsWRKY11, containing the plant-specific WRKY zinc finger DNA–binding motif, was isolated from alfalfa. The MsWRKY11 gene was detected in all plant tissues (root, stem, leaf, flower, and fruit), with high expression in root and leaf tissues. MsWRKY11 was upregulated in response to a variety of abiotic stresses, including salinity, alkalinity, cold, abscisic acid, and drought. Overexpression of MsWRKY11 in soybean enhanced the salt tolerance at the seedling stage. Transgenic soybean had a better salt-tolerant phenotype, and the hypocotyls were significantly longer than those of wild-type seeds after salt treatment. Furthermore, MsWRKY11 overexpression increased the contents of chlorophyll, proline, soluble sugar, superoxide dismutase, and catalase, but reduced the relative electrical conductivity and the contents of malonaldehyde, H2O2, and O2-. Plant height, pods per plant, seeds per plant, and 100-seed weight of transgenic MsWRKY11 soybean were higher than those of wild-type soybean, especially OX2. Results of the salt experiment showed that MsWRKY11 is involved in salt stress responses, and its overexpression improves salt tolerance in soybean.
Soybean is an important economic crop that has a high protein content and is better than any of the other common vegetable sources of protein; and it provides a vital source for human food, cooking oil, animal feed [1,2]. In addition, soybean oil is also used as a fuel source  and even as a source for medicines for its anticancer properties . As a legume, soybean can effective improve nitrogen content in soil by fixing atmospheric nitrogen . Soybean is considered a moderately salt-tolerant crop, but its productivity is critically affected by soil salinity because the germination rate and seed-setting rate decrease under salt stress . In recent years, soil salinization has been rapidly becoming a serious problem, as 20% of cultivated land and 33% of irrigated land are salt-affected and degraded. The land available for agricultural crops has been decreasing every year . The identification and characterization of salt tolerance genes is a crucial step for obtaining salt-tolerant soybean varieties, and transgenic technology is an important means for engineering salt-tolerant soybean lines.
The WRKY family regulates the expression of genes closely related to biotic and abiotic stresses . The functions of WRKY genes have been extensively researched in various plants, including Arabidopsis, rice, soybean, grapevine, sorghum, barley, and maize. However, only a few studies have examined the alfalfa WRKY gene family. Medicago sativa L. Zhaodong has excellent salt tolerance. The protein sequences of GmWRKY65 and MsWRKY11 have many differences, which might explain the higher level of salt tolerance of Zhaodong alfalfa compared to soybean (S1 Fig). In the present study, we successfully cloned a WRKY gene from alfalfa, designated as MsWRKY11. The homologous proteins of MsWRKY11 across various plant families were shown in a phylogenetic tree. Salt tolerance genes having high homology with MsWRKY11 in the phylogenetic tree should be further studied in the future.