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

Abstract

widely distributed in the environment. In some areas of south and southeast Asia, agricultural soils are contaminated with As due to mining, irrigation with As-laden groundwater, and industrial activities, resulting in increased risk of As accumulation in crop plants (Meharg and Rahman, 2003;Williams et al., 2009). High As concentrations in crop plants can present a significant risk to human health through dietary exposure Zhao et al., 2010). In more heavily contaminated soils, crop plants may suffer from phytotoxicity of As, resulting in substantial yield losses (Panaullah et al., 2009; Huhmann et al., 2017). Therefore, it is important to understand how plants cope with As toxicity.Arsenate [As(V)] and arsenite [As(III)] are the main As species present in soil. The two inorganic As species are interconvertible depending on the environmental conditions. As(V) is the predominant form of As in soil under aerobic conditions. As(V) is a chemical analog of phosphate (Pi) and is taken up by Pi transporters. In Arabidopsis (Arabidopsis thaliana), there are nine genes in the PHOSPHATE TRANSPORT1 (PHT1) family (PHT1-PHT9) encoding Pi transporters. PHT1;1 and PHT1;4 contribute to As(V) uptake in Arabidopsis (Shin et al., 2004). After absorption, As(V) is reduced rapidly to As(III) by HIGH ARSENIC CONTENT1 (HAC1)/ARSENATE TOLERANT QUANTITATIVE TRAIT LOCUS1 in Arabidopsis roots (Chao et al., 2014;Sánchez-Bermejo et al., 2014). Plants lacking HAC1 show decreased As(III) efflux, increased sensitivity to As(V), and greatly increased As accumulation in aboveground tissues (Chao et al., 2014;Sánchez-Bermejo et al., 2014). Similarly, several OsHAC proteins in rice (Oryza sativa) play important roles in As(V) reduction, tolerance, and accumulation (Shi et al., 2016;Xu et al., 2017). In contrast to As(V), As(III) is present predominantly as an undissociated neutral molecule under normal environmental conditions and is taken up by plant roots via aquaporin channels (Bienert et al., 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 (Arabidopsis thaliana), arsenate induced chlorosis1 (aic1), in the background of the PC synthase-defective mutant cadmium-sensitive1-3 (cad1-3). Under arsenate stress, aic1 cad1-3 showed larger decreases in chlorophyll content and the number and size of chloroplasts than cad1-3 and a severely distorted chloroplast structure. The aic1 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 aic1 cad1-3 and cad1-3. Using genome resequencing and complementation, TRANSLOCON AT THE OUTER ENVOLOPE MEMBRANE OF CHLOROPLAST132 (TOC132) was identified as the mutant gene, which encodes a translocon protein involved in the import of preproteins from the cytoplasm into the chloroplasts. Proteomic analy...

Melatonin application differentially modulates the enzymes associated with antioxidative machinery and ascorbate‐glutathione cycle during arsenate exposure in indica rice varieties

“…The Chl a and Chl b content significantly declined by 2.6‐fold and 1.6‐fold in Khitish, respectively, and 2.2‐fold and 1.8‐fold in Muktashri, respectively (Table 2). Several studies have shown As‐induced injury to the chlorophyll apparatus due to decline in pigment biosynthesis or activation of enzymes leading to disintegration of the porphyrin ring (Wang et al, 2018). Exogenous Mel lowered the As‐induced loss of Chl a and Chl b content by 1.8‐fold and 1.3‐fold in Khitish, respectively, and 1.8‐fold and 2.4‐fold in Muktashri, respectively (Table 2).…”

“…The Chl a and Chl b content significantly declined by 2.6-fold and 1.6-fold in Khitish, respectively, and 2.2-fold and 1.8-fold in Muktashri, respectively (Table 2). Several studies have shown As-induced injury to the chlorophyll apparatus due to decline in pigment biosynthesis or activation of enzymes leading to disintegration of the porphyrin ring (Wang et al, 2018 2). The reducing power of any species is characteristic of the innate capacity to donate a hydrogen atom to free anionic superoxide radical so as to terminate free-radical reactions (Basu et al, 2010).…”

Season-dependent physiological behavior of Miscanthus x giganteus growing on heavy-metal contaminated areas in relation to soil properties

“…4 ) was quite higher for plants growing on VM comparatively to CAR soil. Arsenic is extremely toxic for chloroplasts where it links to dithiol compounds and enzyme containing closely spaced Cys residues [ 57 ]. Other elements such as Zn may also be toxic in chloroplasts [ 25 ].…”

Molecular mechanisms underlying the toxicity and detoxification of trace metals and metalloids in plants

“…Structural alterations including the absence of palisade structure, reduced leaf thickness, and structural damage in chloroplasts and mitochondria have been observed in plants intoxicated by trace metals (Bini et al, 2012;Wang et al, 2018b), leading to decreased photosynthesis and respiration (Ghori et al, 2019). Chloroplasts appear to be a sensitive target of As toxicity and AtTOC132 (Translocon at the Outer Envelope Membrane of Chloroplast 132) plays a role in protecting chloroplasts from As toxicity in A. thaliana (Wang et al, 2018b). Trace metals at toxic levels also interfere with the uptake and transport of nutrients and water (Perfus-Barbeoch et al, 2002;Lešková et al, 2021).…”