Abstract:

β-1,3-glucanase genes are involved in diverse physiological and developmental processes, including microsporogenesis, pollen germination, fertilization, seed germination, and defense against pathogens. β-1,3-glucanase genes related to plant resistance are the members of a large family of proteins collectively referred to as the pathogenesis- related (PR) proteins. Several β-1,3-glucanase genes have been cloned from cotton, but the majority of them are involved in fiber development and are independent of resistance. Based on the nucleotide sequence which was isolated previously by our laboratory, we cloned one full length cDNA of β-1,3-glucanase gene (GbGLU) from Hai7124 by RACE method. DNA sequence analyses showed that the size of cDNA cloned was 1 266 bp, and it included an open reading frame of 1 086 bp that encoded a polypeptide of 361 amino acids residues with the calculated Mw of 39.66 kD and the predicted pI of 9.15. The deduced amino acid sequence of GbGLU contains conserved domain of Glycosyl hydrolases family 17 and has the N-terminal signal peptide composed of 26 animo acids residues. Southern-blot analysis indicated that there is single copy of GbGLU within cotton genome. The expression analysis of GbGLU gene in cotton root infected by Verticillum dahliae strain VD8 showed that its expression was detectable at 48h and 96h after inoculation. Glucanase genes cloned from cotton could be divided into three classes according to phylogenetic analysis and possess conserved motif of Glycosyl hydrolases family 3, 9, and 17, respectively. In addition, we find that glucanase related with resistance response from cotton and other plants possesses the motif of Glycosyl hydrolases family 17. And therefore, we suggest that conserved motif of Glycosyl hydrolases family 17 might be the function motif contributing to resistance response.

Key words: Cotton, β-1, 3-glucanase, Glycosyl hydrolases