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 ofMTin theOryzagenus remain unclear. Here we identified 53MTgenes from sixOryzagenera, includingO. sativassp.japonica,O. rufipogon,O. sativassp.indica,O. nivara,O. glumaepatula, andO. barthii. TheMTgenes were clustered into four groups based on phylogenetic analysis.MTgenes are unevenly distributed on chromosomes; almost half of theMTgenes were clustered on chromosome 12, which may result from a fragment duplication containing theMTgenes on chromosome 12. Five pairs of segmental duplication events and ten pairs of tandem duplication events were found in the riceMTfamily. The Ka/Ks values of the fifteen duplicatedMTgenes indicated that the duplicatedMTgenes were under a strong negative selection during evolution. Next, combining the promoter activity assay with gene expression analysis revealed different expression patterns ofMTgenes. In addition, the expression ofOsMTgenes was induced under different stresses, including NaCl, CdCl2, ABA, and MeJ treatments. Additionally, we found thatOsMTgenes were mainly located in chloroplasts. These results imply thatOsMTgenes play different roles in response to these stresses. All results provide important insights into the evolution of theMTgene family in theOryzagenus, and will be helpful to further study the function ofMTgenes.Keywords:Oryza sativa;metallothionein (MT);phylogenetic analysis;promoter activity;expression analysis;subcellular localization