Characterization and expression analyses of two plastidic enolase genes in rice

<div><p>To verify the presence of enolase related to the chloroplastic glycolysis in rice, database search was carried out and identified seven putative enolase genes in the rice genome. Among them, <i>OsEno1</i> and <i>OsEno3</i> encode long proteins with N-terminal extensions. GFP protein fusions of these N-terminal extensions were both targeted to plastids of onion epidermal cell. Promoter::<i>GUS</i> analysis showed that <i>OsEno3</i> was highly expressed in young developing leaves, but its expression was drastically decreased during leaf development and greening. On the other hand, the expression of <i>OsEno1</i> was low and detected in limited portions such as leaf sheath at the tiller base. Recombinant OsEno1 protein showed enolase activity with a pH optimum at pH 8.0, whereas OsEno3 did not exhibit detectable activity. Although it remains obscure if OsEno3 encodes a functional enolase <i>in vivo</i>, our results demonstrate that the entire glycolytic pathway does not operate in rice chloroplasts.</p>