Analysis of gene expression profiles for metal tolerance protein in rice seedlings exposed to both the toxic hexavalent chromium and trivalent chromium

The mechanisms of heavy metal tolerance in plants have been characterized extensively and metal tolerance proteins (MTPs) are one group of specific transporters involved in sequestration of heavy metal ions. This study focused on transcriptome analysis of osMTP genes in rice seedlings exposed to hexavalent chromium Cr(VI), or trivalent Cr(III) using real-time quantitative RT-PCR. Distribution of Cr and other mineral elements (Fe, Cu and Mn) in rice seedlings tissues was also determined. Results showed that exposures to both valents of Cr caused significantly more accumulation of Cr in roots rather than shoots, while accumulation and distribution of Fe, Zn and Mn in rice tissues was variable between two Cr treatments. PCR analysis displayed that heterologous expression patterns of individual isogenes from the osMTP gene family were observed in plant tissues as well as in Cr variants. Homologues, LOC_Os02g53490.1 (osMTP8)/LOC_Os03g12530.1 (osMTP8.1) and LOC_Os01g62070.1 (osMTP11)/LOC_Os05g38670.1 (osMT11.1), were also expressed differently under treatments with both forms of Cr. Data analysis indicated that distribution of mineral elements in rice tissues did not agree with changes of expression patterns of these corresponding osMTP genes. These results suggest that inconsistent expression of osMTP genes in rice tissues is largely due to Cr accumulation; at nutrient levels, the role of OsMTPs in storage and transport of mineral elements in plant materials is still open to discussion.