Screening On Cadmium Tolerance Genes In Hyperaccumulator Sedum Alfredii Hance

With the rapid development of the industry and social economy,the problem of heavy metal pollution is becoming more and more serious.Heavy metal not only can be absorbed by plants but also can threat human’s health through the food chain.Phytoremediation is an efficient,economical and environmentally-friendly technique which use plants to absorb and transfer the heavy metals and then repair the contaminated soil.Sedum alfredii Hance is a new Zn/Cd hyperaccumulator which is native in China.The mechanism of its enrichment and tolerance to heavy metal is not clear.In this study,we screened the cDNA library of Sedum alfredii Hance by Saccharomyces cerevisiae,in order to obtain cadmium-tolerant related genes and provide an experimental basis for further research.The yeast which was transformed with empty vector was significantly inhibited on solid media containing 120 Cd.Using this concentration to screening the cDNA library,We obtained 291 transgenic yeast clones.Those cadmium-tolerant related genes were divided into several groups inlcuding genes encode phytochelatins,ribosomal proteins,transcriptional regulators and some functional proteins related to redox,photosynthesis and respiration.In addition,there are 59 genes with unknown function.There are three genes(i.e.X8-1,X152-1,X200-5)can significantly enhance the tolerance for Cd of yeast and respectively encode ferredoxin,annexin and 14-3-3 protein.X8-1 was expressed in the roots,stems and leaves of the hyperaccumulator Sedum alfredii Hance,and its expression level was increased after 50 μM Cd treatment in leaves.However,the expression level of X8-1 is low in anther ecotype,and is not induced by Cd.The expression of X152-1 and X200-5 were similar in roots,stems and leaves of two ecotypes,and were not affected by cadmium stress.The full length sequence for those three genes were cloned by TAIL-PCR technology,we obtain 987 bp for SaFd,2190 bp for SaAnn,and 2175 bp for 14-3-3 protein.At last,we constructed the overexpression plasmid and recombinant plasmid of SaFd for further research.