ARSENATE INDUCED CHLOROSIS 1/ TRANSLOCON AT THE OUTER ENVOLOPE MEMBRANE OF CHLOROPLASTS 132 Protects Chloroplasts from Arsenic Toxicity.

Arsenic (As) is highly toxic to plants and detoxified primarily through complexation with phytochelatins (PCs) and other thiol compounds. To understand the mechanisms of As toxicity and detoxification beyond PCs, we isolated an arsenate-sensitive mutant of Arabidopsis (), (), in the background of the PC synthase-defective mutant (). Under arsenate stress, showed larger decreases in chlorophyll content and the number and size of chloroplasts than and a severely distorted chloroplast structure. The single mutant also was more sensitive to arsenate than the wild type (Columbia-0). As concentrations in the roots, shoots, and chloroplasts were similar between and Using genome resequencing and complementation, () was identified as the mutant gene, which encodes a translocon protein involved in the import of preproteins from the cytoplasm into the chloroplasts. Proteomic analysis showed that the proteome of chloroplasts was more affected by arsenate stress than that of A number of proteins related to chloroplast ribosomes, photosynthesis, compound synthesis, and thioredoxin systems were less abundant in than in under arsenate stress. Our results indicate that chloroplasts are a sensitive target of As toxicity and that AIC1/Toc132 plays an important role in protecting chloroplasts from As toxicity.