Organ-specific expressions and chromosomal locations of two mitochondrial aldehyde dehydrogenase genes from rice (Oryza sativa L.), ALDH2a and ALDH2b.

Recent studies have suggested that mitochondrial aldehyde dehydrogenase (aldehyde:NAD(P)(+) oxidoreductase, EC 1.2.1.3) (ALDH2) plays essential roles in pollen development in plants. Rice (Oryza sativa L.) ALDH2 is encoded by at least two ALDH2 genes, one of which (ALDH2a) was previously identified. In this study, to understand the roles of ALDH2 in rice, we isolated and characterized a cDNA clone encoding another rice ALDH2 (ALDH2b). An in vitro ALDH assay indicated that ALDH2b possesses an NAD(+)-linked activity for oxidation of acetaldehyde, glycolaldehyde and propionaldehyde. Northern blot and immunoblot analyses revealed that ALDH2b was constitutively present in all the organs examined, whereas ALDH2a was expressed in leaves of dark-grown seedlings and panicles. By RFLP linkage mapping, the ALDH2a and ALDH2b genes were mapped to the long arm of chromosome 2 and the short arm of chromosome 6, respectively. We suggest that the rice ALDH2a and ALDH2b genes are orthologues of maize mitochondrial ALDH genes, rf2b and rf2a, respectively.