Abstract
Metallothionein (MT) proteins are low molecular mass, cysteine-rich, and metal-binding proteins that play an important role in maintaining metal homeostasis and stress response. However, the evolutionary relationships and functional differentiation of MT in the Oryza genus remain unclear. Here we identified 53 MT genes from six Oryza genera, including O. sativa ssp. japonica, O. rufipogon, O. sativa ssp. indica, O. nivara, O. glumaepatula, and O. barthii. The MT genes were clustered into four groups based on phylogenetic analysis. MT genes are unevenly distributed on chromosomes; almost half of the MT genes were clustered on chromosome 12, which may result from a fragment duplication containing the MT genes on chromosome 12. Five pairs of segmental duplication events and ten pairs of tandem duplication events were found in the rice MT family. The Ka/Ks values of the fifteen duplicated MT genes indicated that the duplicated MT genes were under a strong negative selection during evolution. Next, combining the promoter activity assay with gene expression analysis revealed different expression patterns of MT genes. In addition, the expression of OsMT genes was induced under different stresses, including NaCl, CdCl2, ABA, and MeJ treatments. Additionally, we found that OsMT genes were mainly located in chloroplasts. These results imply that OsMT genes play different roles in response to these stresses. All results provide important insights into the evolution of the MT gene family in the Oryza genus, and will be helpful to further study the function of MT genes.
Highlights
Metallothioneins (MTs) are a family of low molecular mass (4–8 kD), cysteine (Cys)rich proteins that bind metals via thiol groups of cysteine (Cys) residues [1]
There were 9, 9, 12, 7, 7, and 9 MT members identified in O. sativa ssp.japonica, O. rufipogon, O. sativa ssp. indica, O. nivara, O. glumaepatula, and O. barthii, respectively
Referenced to the genome of japonica rice Nipponbare, we found seven, five, nine, six, and seven collinear gene pairs between O. sativa ssp. japonica and O. rufipogon, Oryza nivara, Oryza sativa ssp. indica, Oryza glumaepatula, and Oryza barthii, respectively (Supplementary Figure S2)
Summary
Metallothioneins (MTs) are a family of low molecular mass (4–8 kD), cysteine (Cys)rich proteins that bind metals via thiol groups of cysteine (Cys) residues [1]. There is increasing evidence that various abiotic stresses can regulate MT gene expression; for example, drought, abscisic acid, salt, environment temperature, and reactive oxygen species [9,10,11,12]. This shows the importance of plant MTs genes in response to abiotic stress. An MT-2 gene (MT2) was upregulated in boron-stressed tomato plants, implying that it may protect against boron stress [13].
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