iTRAQ Analysis Reveals Mechanisms of Growth Defects Due to Excess Zinc in Arabidopsis    

Abstract

(R.T., M.M.)The micronutrient zinc is essential for all living organisms, but it is toxic at high concentrations. Here, to understand the effects of excess zinc on plant cells, we performed an iTRAQ (for isobaric tags for relative and absolute quantification)-based quantitative proteomics approach to analyze microsomal proteins from Arabidopsis (Arabidopsis thaliana) roots. Our approach was sensitive enough to identify 521 proteins, including several membrane proteins. Among them, IRT1, an iron and zinc transporter, and FRO2, a ferric-chelate reductase, increased greatly in response to excess zinc. The expression of these two genes has been previously reported to increase under iron-deficient conditions. Indeed, the concentration of iron was significantly decreased in roots and shoots under excess zinc. Also, seven subunits of the vacuolar H + -ATPase (V-ATPase), a proton pump on the tonoplast and endosome, were identified, and three of them decreased significantly in response to excess zinc. In addition, excess zinc in the wild type decreased V-ATPase activity and length of roots and cells to levels comparable to those of the untreated de-etiolated3-1 mutant, which bears a mutation in V-ATPase subunit C. Interestingly, excess zinc led to the formation of branched and abnormally shaped root hairs, a phenotype that correlates with decreased levels of proteins of several root hair-defective mutants. Our results point out mechanisms of growth defects caused by excess zinc in which cross talk between iron and zinc homeostasis and V-ATPase activity might play a central role.

V-ATPase dysfunction under excess zinc inhibits Arabidopsis cell expansion

“…9 Consistent with this, the protein expression of six V-ATPase subunits, including A, C and E1, was also significantly decreased in the det3-1 mutant. 9 Alternatively, given that the morphologies of the Golgi stacks and Golgi-derived vesicles in vha-A and vha-E1 were abnormal, decreased levels of VHA-A and VHA-E1 expression under conditions of excess zinc might be explained by growth inhibition due to deficient acidification of the TGN. 10,11 In support of this hypothesis, Arabidopsis VHA-E1 and VHA-E3, but not VHA-E2, were found to functionally complement a vma4 zinc-sensitive mutant with a mutation in the single yeast subunit E isoform.…”

“…Moreover, we found that plants suffer an iron deficiency following long-term exposure to excess zinc. 9 Therefore, it is important to explore zincresponsive proteins following short-term treatment. …”

Heavy Metals Induce Iron Deficiency Responses at Different Hierarchic and Regulatory Levels

“…Among the most affected nutrients is iron (Fe), which shares several similarities with other heavy metals regarding chemical structure, behavior, and availability in soils or uptake by plant roots. An excess of several heavy metals can induce chlorosis in younger leaves (Schaaf et al, 2006;Meda et al, 2007;Morrissey et al, 2009;Fukao et al, 2011;Wu et al, 2012), hence resembling the most typical visual symptom of Fe deficiency (Vert et al, 2002;Wu et al, 2012). Even in the absence of visual symptoms, heavy metals can negatively interfere with Fe homeostasis, as seen in the case of manganese (Mn; Allen et al, 2007;Lanquar et al, 2010).…”

Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu, Mn, and Zn

“…The ZIP transporter family includes the best candidates for facilitating Zn influx into the plant cytoplasm. In addition to its role in Fe acquisition, AtIRT1 is also responsible for the uptake of Zn from the soil solution (Fukao et al, 2011). The broad selectivity of AtIRT1 allows this transporter to mediate the uptake of several divalent metal cations, including Zn (Barberon et al, 2011;Shanmugam et al, 2011).…”