The rice Rim2 transcript accumulates in response to Magnaporthe grisea and its predicted protein product shares similarity with TNP2-like proteins encoded by CACTA transposons.

Abstract

A rice transcript, Rim2, was identified that accumulated in both incompatible and compatible interactions between rice and Magnaporthe grisea. The Rim2 transcript also accumulated in response to treatment with a cell wall elicitor derived from M. grisea. A 3.3-kb RIM2 cDNA clone was isolated and is predicted to encode a protein of 653 amino acids, which shares 32 55% identity with TNP2-like proteins encoded by CACTA transposons of other plants. A 1.05-kb segment of the Rim2 sequence shows 82% nucleotide sequence identity with sequences flanking the A1 and C members of the rice Xa21 disease resistance gene family. The 5'-upstream region of Rim2 was cloned and the transcriptional start sites were identified. The 5' and 3' noncoding termini of Rim2 are AT-rich. A cis-element showing similarity to a sequence that mediates defense-associated transcriptional activation of the tobacco retrotransposon Tnt1, and four motifs that fit the consensus sequence of the elicitor-responsive elements in the promoters of the parsley PR-1 genes were found in the 5'-upstream region. Four imperfect tandem repeats were identified in the 3' noncoding terminus. Southern analysis with genomic DNA from different rice species indicated that Rim2 is present in 3-4 copies per genome. These results suggest that Rim2 may be one component of a large CACTA-like element, whose transcript accumulates in response to attack by pathogens.