Genetic Interactions Between Genes Involved In Cadmium Tolerance In Saccharomyces Cerevisiae

Cadmium, as a serious environmental toxicant, causes carcinogenic effects on humans. Cadmium can accumulate in vivo to affect growth, development or reproduction, and also induce excess reactive oxygen species(ROS) production. But the molecular and cytotoxic mechanism is not quite clear. Mitogen-activate protein(MAP) kinases are important signaling molecules regulating cell survival, proliferation and differentiation, and they can be activated by cadmium stress.Cell wall integrity pathway(CWI) and high osmolarity glycerol pathway(HOG), which are two MAPK signaling pathways that are involved in the response to cadmium stress in Saccharomyces cerevisiae. The research object are six CWI genes, MID2, BCK1, SLT2, RLM1, SWI4, SWI6, and seven HOG genes, SHO1, STE20, STE50, SSK1, SSK2, PBS2, HOG1. In this study, we created 369 paired double- gene deletion mutants through SGA approach. Through serial dilution assay, we found that these 13 genes have genetic interactions with genes involved in metabolism, protein fate, transcriptional regulation and cellular transport. In addition, we tested the cadmium sensitivity of 42 paired double-gene deletion mutants between six CWI genes and seven HOG genes. Our results indicate that the CWI pathway is epistatic to the HOG pathway in cadmium sensitivity. However, gene deletion mutations for the Swi4/Swi6 transcription factor complex, which is partially controlled by the CWI pathway, show synergistic effects with deletion mutations of HOG genes, STE20, STE50, PBS2 and HOG1, in cadmium sensitivity. Through Western blot analysis, we found that the cadmium- induced CWI activation is independent on the HOG pathway and the calcium/calcineurin signaling pathway in yeast cells. Furthermore, cadmium can induce excess intracellular ROS production. Both CWI and HOG pathways play a negative role in cadmium- induced ROS production. ROS contents of 8 double- gene deletion mutants, bck1ste20, slt2 ste20, slt2 ste50, swi4 ste20, swi4 ste50, swi6 ste50, swi6 pbs2, swi6 hog1, are higher than their corresponding single gene deletion mutants, while no ROS is induced by cadmium in 9 double- gene deletion mutants, mid2 ste50, mid2 ssk1, mid2 pbs2, mid2 hog1, bck1 sho1, bck1 ste50, bck1 ssk1, bck1 ssk2, slt2 hog1. Therefore, genetic interactions also occur between these genes in ROS production.