Structure of a rice ?-glucanase gene regulated by ethylene, cytokinin, wounding, salicylic acid and fungal elicitors

Abstract

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.

Salicylic Acid in Rice (Biosynthesis, Conjugation, and Possible Role)

“…Increases in both chitinase and glucanase activities were detected only in P. syringae-inoculated leaves and not systemically. However, the transcription of a chitinase (Nishizawa and Hibi, 1991) and a glucanase (Simmons et al, 1992) was induced in rice by pathogen-derived elicitors and SA. Additionally, application of 2,6-dichloro-isonicotinic acid, a possible SA analog that activates natural plant defenses, induced resistance in rice to M .…”

Sucrose and Cytokinin Modulation of WPK4, a Gene Encoding a SNF1-Related Protein Kinase from Wheat

“…Phytohormones are also thought to be indispensable in signaling pathways that involve perception and transduction of external signals (Klee and Estelle, 1991). Cytokinins have attracted particular interest because of their diverse physiological functions in response to light (Miller, 1956;Su and Howell, 1995;von Arnim and Deng, 1996), nutrients (Yu et al, 1998), growth (Chaudhury et al, 1993;Brzobohaty et al, 1994), and even wounding (Simmons et al, 1992). Recent work has revealed that cytokinins enhance the transcription of several genes involved in nutrient metabolism (Lu et al, 1990;Dominov et al, 1992;Andersen et al, 1996;Ehnes and Roitsch, 1997) and self-defense (Simmons et al, 1992;Sano et al, , 1996.…”

Breakdown of Cell Wall Polysaccharides in Rice Culms at the Early Ripening Stage

“…A decrease in the hemicellulose content in rice culms may result from a higher rate of β-glucan degradation, from a lower rate of β-glucan synthesis, or both. Previously, we found that the Gns1 gene, a putative 1,3;1,4-β-glucanase gene of rice (Simmons et al, 1992), is highly expressed in ripening rice culms (Nemoto et al, 1999;Baba et al, 2001), which suggests that the higher rate of β-glucan degradation might be the main cause of the decrease in the hemicellulose content in ripening culms. The rate of β -glucan degradation might be very high in ripening culms, presumably because of its translocation to the panicle.…”