Identification of plant genes involved in nonhost disease resistance

Plants employ the more complex and evolutionarily more robust system of nonhost resistance against a broad range of pathogenic species. Nonhost resistance, shown by an entire plant species to a specific parasite or pathogen, is the most common and durable form of plant resistance to diseases. In spite of tremendous progress in plant science, nonhost pathogen resistance is still very poorly understood in contrast with the host resistance, shown by specific genotypes within an otherwise susceptible host species. Host resistance is often governed by single resistance (R) genes, the products of which directly or indirectly interact with specific elicitors produced by avirulence (avr) genes. Considerable progress has been made in our understanding of gene-for-gene resistance (R-avr interactions). In spite of this progress, it is still not clear why a pathogen fully virulent on one plant species is nonpathogenic on others. To date, nonhost resistance is one of the least understood phenomena in the area of plant-microbe interactions.

Recently several components of nonhost disease resistance have been identified. Nonhost resistance exhibited against bacteria, fungi and oomycetes can be of two types. Type I nonhost resistance does not produce any visible symptoms whereas type II nonhost resistance results in a rapid hypersensitive response with cell death. Strong similarities exist between nonhost and gene-for-gene resistance responses but it is still not clear if the same mechanism is involved in producing these resistance responses. We are using a VIGS-based forward and reverse genetics approach to identify plant genes involved in nonhost disease resistance in Nicotiana benthamiana. The information gained from this project on the molecular mechanisms of nonhost resistance will help to engineer plants for more durable resistance to combat infectious plant diseases and therefore lead to significant improvement of agricultural production.

This project is funded by the Samuel Roberts Noble Foundation and BARD.