Induced expression of a temperature-sensitive leucine-rich repeat receptor-like protein kinase gene by hypersensitive cell death and wounding in tobacco plant carrying the N resistance gene

A gene encoding a receptor-like protein kinase was isolated as the gene induced in the early period of N gene-dependent hypersensitive cell death in tobacco leaves. The kinase domain expressed as a glutathione S-transferase fusion protein was capable of autophosphorylation, indicating that this gene encodes an active protein kinase. A high level of the transcript accumulated before necrotic lesion formation in tobacco mosaic virus (TMV)-inoculated tobacco leaves carrying the N gene but it was low in a tobacco cultivar lacking the N gene. A small but reproducible increase in the transcript was found 1-2 h after a temperature shift from 30degreesC to 20degreesC even in healthy leaves, suggesting the gene expression is temperature sensitive. The gene was named WRK for wound-induced receptor-like protein kinase, because the transcript increased to a maximum within 15-30 min of wounding. In suspension cultured tobacco cells, an increase in the transcript was found 15 min after transfer to a new medium, but it was suppressed under high osmotic pressures. The wound-induced WRK accumulation was enhanced by cycloheximide treatment, but not by known defense signal compounds (salicylic acid, jasmonic acid, 1-aminocyclopropan-1-carboxylic acid and abscisic acid) and some plant hormones. Thus, WRK is a wound-inducible and temperature-sensitive protein kinase gene induced before hypersensitive cell death probably through unknown signaling pathways.