Exploring the salt- and drought-tolerant genes of alfalfa through expression library screening strategy

Salinity and drought stress are major abiotic stresses negatively affecting the growth and productivity of alfalfa (Medicago sativa L.). Exploration of genes exhibiting superior tolerance to salinity and drought stress in alfalfa will help aid target molecular breeding and developing tolerant forages. In this study, we adopted a high-efficient yeast FOX hunting system for the identification of salinity and drought tolerant genes in alfalfa. Based on the Gateway-compatible vector system, a high-quality expression library was constructed, containing 1.3 × 107 clones with an average size of 1.44 kb. Through heterologous transformation of mixed library plasmid into salt or drought sensitive yeast mutants, monoclonal resistant strains were screened and tolerant genes were captured. Eighteen salinity-tolerance genes were obtained which were involved in several pathways, containing GRAS and zinc finger transcriptional factors, PP2A interaction module, ERVT vesicle transporter and LETM transmembrane protein. Twelve drought tolerance genes were separated, including ERF and SCL transcriptional factors, CIPK and BSK protein kinases, TGL-type ligase, cPGM and cPDL protease. The mRNA transcription levels of these tolerant genes were inducible or suppressible for response to salt or drought stress conditions following quantitative PCR detection, respectively. Furthermore, heterologous transformation of ERVT and CIPK11 can improve the salt and drought stress tolerance in Arabidopsis, which indicates the conservative function of the screening gene in yeast and Arabidopsis. Obtaining these candidate genes can provide new insights for future research with respect to plant salt and drought tolerance.