Cloning of a pathogenesis-related protein-1 gene from Nicotiana glutinosa L. and its salicylic acid-independent induction by copper and β-aminobutyric acid

Abstract

Induction of pathogenesis-related (PR) protein gene expressions are one of the unique features of disease resistant reactions of plants against pathogen infection. To better understand the molecular mechanism of plants by monitoring expression of PR protein gene, we isolated a PR-1 cDNA from TMV-induced Nicotiana glutinosa cDNA library using PCR-based method. Southern blot hybridization showed that there may present 2 copies of PR-1 gene in diploid plant N. glutinosa and possibly 4 copies in amphidiploid plant N. tabacum. Nucleotide sequence analysis showed that the PR-1 clone is 682 bp in length which containing one open reading frame of 168 amino acids. Deduced amino acid sequence of this cDNA has 88 % identity with PR-1 protein from N. tabacum cv. Samsun NN. Northern blot hybridization revealed that PR-1 mRNA of N. glutinosa is induced by TMV infection in TMV resistant but not in susceptible tobacco cultivar. However, salicylic acid(SA) treatment induces this gent both in TMV resistant and susceptible tobacco cultivars. Some chemicals were tested as possible inducers, resulting in identification of copper and β-aminobutyric acid(β-ABA) as potent inducers of tobacco PR gene expression. Temporal expression studies of PR-1 and glucanase (PR-2) genes in tobacco revealed that induction of PR gene expressions in tobacco by copper and β-ABA treatment are not dependent on accumulation of endogenous SA following treatment of those chemicals. This result suggests that there may exist an SA-independent signal transduction pathway leading to induce expression of PR-genes in tobacco.