A new elicitor of the hypersensitive response in tobacco: a fungal glycoprotein elicits cell death, expression of defence genes, production of salicylic acid, and induction of systemic acquired resistance.

A 32 kDa glycoprotein whose effects in tobacco and other Nicotianae mimic a typical hypersensitive response, was isolated from Phytophthora megasperma. Infiltration of a few nanograms of the protein into leaves caused the formation of lesions that closely resemble hypersensitive response lesions. Transcripts of genes encoding enzymes of the phenylpropanoid and sesquiterpenoid pathways accumulated rapidly after elicitor application followed by salicylic acid production. Cellular damage, restricted to the infiltrated zone, occurred only several hours later, at a time when expression of PR protein genes was activated. After several days systemic acquired resistance was also induced. Thus, tobacco plant cells that perceived the glycoprotein generated a cascade of signals acting at local, short, and long distances, and causing the coordinate expression of specific defence responses in a way similar to hypersensitivity to tobacco mosaic virus. The glycoprotein represents a powerful tool to investigate further the signals and their transduction pathways involved in induced disease resistance. It may also be useful to engineer broad disease protection in a Nicotianae and possibly into crop plant species.