Characterization and expression of beta-1,3-glucanase genes in peach

beta -1,3-glucanase is one of the pathogenesis-related (PR) proteins involv ed in plant defense responses. A peach beta -1,3-glucanase gene, designated PpGnsl, has been isolated and characterized. The deduced amino acid sequen ce of the product of PpGns indicates that it is a basic isoform (pI 9.8), a nd contains a putative signal peptide of 38 amino acids but has no C-termin al extension. Amino acid sequence comparisons revealed that PpGnsl is 69% a nd 67% identical to citrus and soybean (beta -1,3-glucanases, respectively. Southern analysis of total genomic DNA also indicates that at least three genes for beta -1,3-glucanases exist in peach, forming a small gene family. Characterization of four additional clones by PCR has identified a second beta -1,3-glucanase gene, PpGns2. PpGns2 has been partially sequenced, and when compared to PpGnsl, it shows high sequence homology, 96% and 99% nucle otide identity in the first and (partial) second exons, respectively. The d educed partial sequence of the PpGns2 product displays only two differences from PpGnsl in the signal peptide and one in the (partial) mature protein (141 amino acids). The 5'-flanking promoter regions of these two genes shar e 90% identity in nucleotide sequences interrupted by five major gaps (4-10 9 nt long). The promoter region contains various sequences similar to cis-r egulatory elements present in different stress-induced plant genes. In leav es and stems of peach shoot cultures grown in vitro, PpGnsl is induced with in 12 h after exposure to a culture filtrate of Xanthomonas campestris pv. pruni or ethephon. However, it is not induced following treatment with merc uric chloride.