EXPRESSION OF EXPANSIN GENES IS CORRELATED WITH GROWTH IN DEEP-WATER RICE

Expansins are a family of proteins that catalyze long-term extension o f isolated cell walls. previously, two expansin proteins have been iso lated from internodes of deepwater rice, and three rice expansin genes , Os-EXP1, Os-EXP2, and Os-EXP3, have been identified. We report here on the identification of a fourth rice expansin gene, Os-EXP4, and on the expression pattern of the rice expansin gene family in deepwater r ice. Rice expansin genes show organ-specific differential expression i n the coleoptile, root, leaf, and internode, In these organs, there is increased expression of Os-EXP1, Os-EXP3, and Os-EXP4 in developmenta l regions where elongation occurs. This pattern of gene expression is also correlated with acid-induced in vitro cell wall extensibility. Su bmergence and treatment,with gibberellin, both of which promote rapid internodal elongation, induced accumulation of Os-EXP4 mRNA before the rate of growth started to increase. Our results indicate that the exp ression of expansin genes in deepwater rice is differentially regulate d by developmental, hormonal, and environmental signals and is correla ted with cell elongation.