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.