Identification of the metallothionein gene family from cucumber and functional characterization of in under salinity and osmotic stress.

Metallothionein (MT) proteins are low-molecular-weight, cysteine-rich and metal-binding proteins that play important roles in the maintenance of metal homeostasis and detoxification, but their roles in abiotic stress tolerance remain largely unknown. In this study, three family genes (, and ) were identified in the cucumber genome. CsMT2, CsMT3 and CsMT4 possessed 14, 10, and 18 Cys residues, which were clustered into 2, 2, and 3 Cys-rich regions, respectively. Phylogenetic analysis of MTs from cucumber, and soybean revealed that these MTs were clustered into four groups in accordance with the MT types (types 1-4). An analysis of the -acting regulatory elements revealed that a series of hormone-, stress-, and development-related -elements were present in the promoter regions of genes. Expression pattern analysis by RT-PCR showed that the genes exhibited different tissue expression patterns. showed relatively higher expression in stem, leaf, and flower; was mainly expressed in leaf, flower, and fruit, while was highly expressed in fruit and leaf. The qRT-PCR results showed that the genes were induced by various stress treatments including NaCl, PEG, and ABA, while displayed much higher expression levels in response to these stresses than and . cells expressing exhibited higher salinity and osmotic tolerance compared with control cells, indicating the significant function of CsMT4 to confer tolerance to these stresses. These results lay a foundation for further research on the function of family genes in plant stress responses.