Root exudates influence the surrounding soil microbial community, and recent evidence demonstrates the involvement of ATPbinding cassette (ABC) transporters in root secretion of phytochemicals. In this study, we examined effects of seven Arabidopsis (Arabidopsis thaliana) ABC transporter mutants on the microbial community in native soils. After two generations, only the Arabidopsis abcg30 (Atpdr2) mutant had significantly altered both the fungal and bacterial communities compared with the wild type using automated ribosomal intergenic spacer analysis. Similarly, root exudate profiles differed between the mutants; however, the largest variance from the wild type (Columbia-0) was observed in abcg30, which showed increased phenolics and decreased sugars. In support of this biochemical observation, whole-genome expression analyses of abcg30 roots revealed that some genes involved in biosynthesis and transport of secondary metabolites were up-regulated, while some sugar transporters were down-regulated compared with genome expression in wild-type roots. Microbial taxa associated with Columbia-0 and abcg30 cultured soils determined by pyrosequencing revealed that exudates from abcg30 cultivated a microbial community with a relatively greater abundance of potentially beneficial bacteria (i.e. plant-growth-promoting rhizobacteria and nitrogen fixers) and were specifically enriched in bacteria involved in heavy metal remediation. In summary, we report how a single gene mutation from a functional plant mutant influences the surrounding community of soil organisms, showing that genes are not only important for intrinsic plant physiology but also for the interactions with the surrounding community of organisms as well.

Screening an Arabidopsis (Arabidopsis thaliana) T-DNA mutant library for selenate resistance enabled us to isolate a selenateresistant mutant line (sel1-11). Molecular and genetic characterization showed that the mutant contained a lesion in the SULTR1;2 gene that encodes a high affinity root sulfate transporter. We showed that SULTR1;2 is the only gene among 13 mutated genes of the Arabidopsis sulfate transporter family whose mutation conferred selenate resistance to Arabidopsis. The selenate resistance phenotype of the sel1-11 mutant was mirrored by an 8-fold increase of root growth in the presence of selenate as shown by the calculated lethal concentration values. The impairment of SULTR1;2 activity in sel1-11 resulted in a reduced 35 S-sulfate uptake capacity by both roots and calli and a reduced sulfate and selenate content in root, shoot, and calli. Comparing sulfate-to-selenate ratios instead of absolute sulfate and selenate contents in roots and shoots enabled us to gain better insight into the mechanism of selenate toxicity in Arabidopsis. Roots of the sel1-11 mutant line showed a higher sulfate to selenate ratio than that of wild-type roots, while there were no significant differences in sulfate to selenate ratios in shoots of wild-type and mutant lines. These results indicated that the mechanism that confers the selenate resistance phenotype to the sel1-11 line takes place rather in the roots. It might be in part the result of a lower selenate uptake and of a protective effect of sulfate against the toxic effects of selenate on root growth. These results revealed in plants a central and specific role of the transporter SULTR1;2 in selenate sensitivity; they further suggested that root growth and potentially the root tip activity might be a specific target of selenate toxicity in Arabidopsis.