Interaction of ONION2 Ketoacyl CoA Synthase with KCR1 Ketoacyl CoA Reductase in Rice

Fatty acid elongases (FAEs), which catalyze elongation reactions of a carbon chain of very-long-chain fatty acids, play an important role in shoot development in rice. The elongation reactions consist of four sequential reactions; the first step is catalyzed by ketoacyl CoA synthase (KCS), the second by ketoacyl CoA reductase (KCR), the third by hydroxyacyl CoA dehydrase (HCD) and the last by enoyl CoA reductase (ECR), and these enzymes are assumed to form an elongation complex. However, no interacting proteins of ONION1 (ONI1) and ONI2, which encode KCS and are required for shoot development in rice, are reported.

A database search identified 10 KCR genes in the rice genome. Among the genes, the expression pattern of KCR1 was similar to that of ONI2. Yeast two-hybrid analysis showed interaction of ONI2 with KCR1, which was confirmed by GST pull-down assay. These results suggest that ONI2 and KCR1 form an FAE complex that is required for shoot development in rice.