A NOVEL MT GENE OF RICE PLANTS IS STRONGLY EXPRESSED IN THE NODE PORTION OF THE STEM

We identified a cDNA encoding a metallothionein (MT)-like protein from a cDNA library of rice endosperm. This cDNA (ricMT) encoded an open r eading frame of 80 amino acids, with two cysteine-rich domains at the amino-terminus and carboxy-terminus, respectively. The deduced amino a cid sequence was homologous to those of class I MT-like proteins. Sout hern blot analysis revealed that the gene exists at one locus in the r ice genome. Northern blot analysis with rice seedlings showed that the transcript level in shoots was elevated by the addition of metal ions , such as Cu, Zn, Cd, Fe, Pb and Al, whereas in roots it was reduced i n the presence of metal ions other than copper. The expression level o f ricMT in mature rice plants was extremely high in stems relative to leaf blades, leaf sheaths, endosperm and roots. In the first nodes, th e yield of the transcript was 150-times higher than that in leaf blade s. These results suggest that ricMT protein may play an important role in the metabolism of metal elements in the stem. (C) 1997 Elsevier Sc ience B.V.