Expression of β-expansins is correlated with internodal elongation in deepwater rice

Fourteen putative rice (Oryza sativa) beta -expansin genes, Os-EXPB1 through Os-EXPB14, were identified in the expressed sequence tag and genomic databases. The DNA and deduced amino acid sequences are highly conserved in all 14 beta -expansins. They have a series of conserved C (cysteine) residues in the N-terminal half of the protein, an HFD (histidine-phenylalanine-aspartate) motif in the central region, and a series of W (tryptophan) residues near the carboxyl terminus. Five beta -expansin genes are expressed in deepwater rice internodes, with especially high transcript levels in the growing region. Expression of four beta -expansin genes in the internode was induced by treatment with gibberellin and by wounding. The wound response resulted from excising stem sections or from piercing pinholes into the stem of intact plants, The level of wound-induced beta -expansin transcripts declined rapidly 5 h after cutting of stem sections. We conclude that the expression of beta -expansin genes is correlated with rapid elongation of deepwater rice internodes, it is induced by gibberellin and wounding, and wound-induced beta -expansin mRNA appears to turn over rapidly.