STRUCTURE OF A RICE BETA-GLUCANASE GENE REGULATED BY ETHYLENE, CYTOKININ, WOUNDING, SALICYLIC-ACID AND FUNGAL ELICITORS

A rice beta-glucanase gene was sequenced and its expression analyzed at the level of mRNA accumulation. This gene (Gns1) is expressed at relatively low levels in germinating seeds, shoots, leaves, panicles and callus, but it is expressed at higher levels in roots. Expression in the roots appears to be constitutive. Shoots express Gns1 at much higher levels when treated with ethylene, cytokinin, salicylic acid, and fungal elicitors derived from the pathogen Sclerotium oryzae or from the non-pathogen Saccharomyces cereviseae. Shoots also express Gns1 at higher levels in response to wounding. Expression in the shoots is not significantly affected by auxin, gibberellic acid or abscisic acid. The beta-glucanase shows 82% amino acid similarity to the barley 1,3;1,4-beta-D-glucanases, and from hybridization studies it is the beta-glucanase gene in the rice genome closest to the barley 1,3;1,4-beta-glucanase EI gene. The mature peptide has a calculated molecular mass of 32 kDa. The gene has a large 3145 bp intron in the codon for the 25th amino acid of the signal peptide. The gene exhibits a very strong codon bias of 99% G + C in the third position of the codon in the mature peptide coding region, but only 61% G+C in the signal peptide region.