Abstract
Zinc (Zn) is an essential element for plant growth and development, and Zn derived from crop plants in the diet is also important for human health. Here, we report that genetic variation in Heavy Metal-ATPase 4 (HMA4) controls natural variation in leaf Zn content. Investigation of the natural variation in leaf Zn content in a world-wide collection of 349 Arabidopsis thaliana wild collected accessions identified two accessions, Van-0 and Fab-2, which accumulate significantly lower Zn when compared with Col-0. Both quantitative trait loci (QTL) analysis and bulked segregant analysis (BSA) identified HMA4 as a strong candidate accounting for this variation in leaf Zn concentration. Genetic complementation experiments confirmed this hypothesis. Sequence analysis revealed that a 1-bp deletion in the third exon of HMA4 from Fab-2 is responsible for the lose of function of HMA4 driving the low Zn observed in Fab-2. Unlike in Fab-2 polymorphisms in the promoter region were found to be responsible for the weak function of HMA4 in Van-0. This is supported by both an expression analysis of HMA4 in Van-0 and through a series of T-DNA insertion mutants which generate truncated HMA4 promoters in the Col-0 background. In addition, we also observed that Fab-2, Van-0 and the hma4-2 null mutant in the Col-0 background show enhanced resistance to a combination of high Zn and high Cd in the growth medium, raising the possibility that variation at HMA4 may play a role in environmental adaptation.
Highlights
Zinc (Zn) is an essential micronutrient for plants, as it plays important roles in many biological processes, including as a co-factor of various enzymes and transcription factors (Broadley et al, 2012)
We have used ionomics coupled with genome-wide association (GWA) analysis and linkage mapping to successfully identify multiple genes that control natural variation in leaf elemental contents in A. thaliana (Rus et al, 2006; Baxter et al, 2008, 2010; Chao et al, 2012, 2014b; Forsberg et al, 2015)
We performed GWA mapping of leaf Zn concentration, but did not detect any significant association using either the linear model or the mixed model approaches. This is a result of rare alleles controlling the variation in leaf Zn concentration, which is similar to what we have observed for the GWA mapping of leaf sulfur and selenium concentrations (Chao et al, 2014a)
Summary
Zinc (Zn) is an essential micronutrient for plants, as it plays important roles in many biological processes, including as a co-factor of various enzymes and transcription factors (Broadley et al, 2012). High concentrations of Zn are toxic to plants (Lin and Aarts, 2012). The Zn concentration in plant cells is finely tuned. Zn is an essential micronutrient crucial for the health of livestock and humans, and plants are a major dietary source of Zn. understanding the mechanism of Zn accumulation in plants is important for plant nutrition but is of significance for human health and the health of livestock animals.
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