Cloning and characterization of disease-response genes in plants could
be an initial step toward understanding the complex disease resistanc
e mechanism. To better understand the complex step, we isolated one of
the pathogenesis-related proteins, beta-1,3-glucanase, cDNA from a cD
NA library of Nicotiana glutinosa showing systemic resistance. One clo
ne (GN-3) was a partial cDNA of beta-1,3-glucanase 800 bp in size with
a 171 amino acid coding region. This clone had a 90% nucleotide homol
ogy with the beta-1,3-glucanase gene of N. tabacum cv. BY4. A deduced
amino acid sequence of GN-3 clones indicated a 91% identity with the b
eta-1,3-glucanase of tobacco, 58% with that of Lycopersicon esculentum
, and 51% with that of Glycine max. Northern blot analysis showed that
expression of beta-1,3-glucanase mRNAs was induced by TMV infection a
nd salicylic acid treatment. In addition to that this gene was highly
induced by CuSO4 and beta-aminobutyric acid which are known as inducer
s of plant disease resistance. The possible role of this gene expressi
on in relation to chemical-induced plant defense responses is discusse
d.