Functional analysis of the rice metallothionein gene OsMT2b promoter in transgenic Arabidopsis plants and rice germinated embryos.

In this paper, the promoter of a type 2 metallothionein gene OsMT2b was cloned in indica rice Jiayu948 and its function was analyzed in transgenic Arabidopsis plant and rice germinated embryo aided by a GUS reporter gene. The result shows that the full promoter drives GUS expression predominantly in the vascular tissues of Arabidopsis, and the expression undergoes a unimodal pattern during the development, with peaking in the mature tissues in leaves and floral organs. Further promoter deletion analysis in Arabidopsis displays different function regions that are crucial for regulating gene expression: the -212/-21 region for keeping the minimal promoter activity and the expression in the initiation site of lateral root; the -924/-213 region for the expression in vegetative and reproductive organs; the -1227/-925 region for confining high expression in silique; and the -1502/-1228 and -1227/-925 regions for the balanceable control of high expression in embryo. And by using a transient expression system in rice germinated embryo, the similar promoter region-based regulation was observed. In addition, from studying the promoter activities under different stress conditions such as ABA, GA, ZT, PEG, cold, hot, NaCl, Cu, Zn and wounding, it is proposed that environmental stresses may regulate OsMT2b expression through the promoter cis-acing elements.