IDENTIFICATION AND GENE-EXPRESSION OF ANAEROBICALLY INDUCED ENOLASE IN ECHINOCHLOA-PHYLLOPOGON AND ECHINOCHLOA-CRUS-PAVONIS

Enolase (2-phospho-D-glycerate hydrolase, EC 4.2.1.11) has been identi fied as an anaerobic stress protein in Echinochloa oryzoides based on the homology of its internal amino acid sequence with those of enolase s from other organisms, by immunological reactivity, and induction of catalytic activity during anaerobic stress. Enolase activity was induc ed 5-fold in anoxically treated seedlings of three flood-tolerant spec ies (E. oryzoides, Echinochloa phyllopogon, and rice [Oryza sativa L.] ) but not in the flood-intolerant species (Echinochloa crus-pavonis). A 540-bp fragment of the enolase gene was amplified by polymerase chai n reaction from cDNAs of E. phyllopogon and maize (Zea mays L.) and us ed to estimate the number of enolase genes and to study the expression of enolase transcripts in E. phyllopogon, E. crus-pavonis, and maize. Southern blot analysis indicated that only one enolase gene is presen t in either E. phyllopogon or E. crus-pavonis. Three patterns of enola se gene expression were observed in the three species studied. In E. p hyllopogon, enolase induction at both the mRNA and enzyme activity lev els was sustained at all times with a further induction after 48 h of anoxia. In contrast, enolase was induced in hypoxically treated maize root tips only at the mRNA level. In E. crus-pavonis, enolase mRNA and enzyme activity were induced during hypoxia, but activity was only tr ansiently elevated. These results suggest that enolase expression in m aize and E. crus-pavonis during anoxia are similarly regulated at the transcriptional level but differ in posttranslational regulation, wher eas enolase is fully induced in E. phyllopogon during anaerobiosis.