Characterization of PvACR3, a gene involved in arsenic tolerance and hyperaccumulation in Pteris vittata.

摘要

Arsenic, a known toxin and carcinogen, is one of many elements that plants are exposed to in their environment. Pteris vittata (Pteridacae) is unique because it and its close relatives are the only known plant species that are able to tolerate and hyperaccumulate up to 2% of their foliar dry weight as arsenic. The focus of the research presented in this thesis is to understand the fundamental mechanisms that are necessary for P. vittata to tolerate and hyperaccumulate arsenic, specifically involving the arsenite effluxer that was identified and named PvACR3. Since PvACR3 complements a yeast mutant for ScACR3 and its expression is induced by the addition of arsenic, it is likely to be involved in arsenic tolerance and hyperaccumulation in P. vittata. To determine if PvACR3 is necessary for arsenic tolerance and hyperaccumulation, a system for RNAi in P. vittata gametophytes was established and used to knock down the expression of the endogenous PvACR3 gene. Targeting the endogenous PvACR3 gene by RNAi results in PvACR3 gametophytes that either die or show diminished growth in the presence of 500mM arsenite compared to gametophytes grown on arsenite free media. These data indicate that PvACR3 is necessary for arsenic tolerance in P. vittata. Interestingly, homologues of ACR3 genes do not exist in angiosperms, which may explain why angiosperms are unable to tolerate or hyperaccumulate such high levels of arsenic. To determine if PvACR3 is sufficient for arsenic tolerance, PvACR3 was transformed into a non-accumulator Arabidopsis thaliana. Preliminary data indicate that PvACR3 confers a degree of tolerance when grown on low levels of arsenite; however, further characterization is needed to determine how PvACR3 confers arsenic tolerance in Arabidopsis.