Plants contain a broad repertoire of immune receptors (R genes) that mediate recognition of disease-causing organisms (pathogens). The major class of R genes is the NB-LRR (nucleotide-binding, leucine rich repeat) type, and an individual plant contains hundreds of different receptors. Activation of an NB-LRR receptor by a pathogen generally results in resistance to that pathogen, so the complement of NB-LRRs a plant possesses is a major determinant of which diseases it resists or succumbs to. Both pathogens and R genes evolve rapidly. Knowledge of R gene diversity within and across species would provide insight into the evolution of these important genes, improve our understanding of plant resistance, and aid the development of disease-resistant crops. However, the diversity of NB-LRRs within a given species and across related species is still poorly understood. Despite the advances in genome sequencing and explosion of available sequence data, until recently NB-LRR genes have been hard to sequence and annotate for technical reasons, because they are relatively similar to one another and are often found in clusters of highly similar alleles.
Scientists at the Sainsbury Laboratory in Norwich have developed a fast, accurate, and cost-efficient technique for isolating and sequencing just the NB-LRR genes from a plant. Using this method, termed Resistance Gene Enhancement Sequencing (RenSeq), our collaborators will sequence resistance genes from hundreds of different plants within three important plant families. The analysis will focus on crop plants and their wild relatives in three important plant families: the Solanaceae (tomatoes, potatoes, and their relatives) Triticeae (wheat, barley and related grains) and Brassicaceae (mustard greens, cabbage, turnips, canola and their relatives). The analysis will include different individual isolates from a given species that evolved in different places, in order to elucidate the diversity within species as well as between species. The results will be made publicly available in a database to assist others analyzing or breeding for disease resistance in these species.
Our collaborators intend to use the large dataset they will generate to answer important questions about R gene evolution, such as whether certain R gene families are evolving rapidly under pathogen pressure, whether some R genes have costs to the host plant in the absence of pathogen pressure, whether some classes of R genes have been selected or lost during domestication of crops, and whether there are novel classes of R genes that have not yet been described.
Jones JDG, Vance RE, Dangl JL (2016). Intracellular innate immune surveillance devices in plants and animals. Science 354: aaf6395. doi: 10.1126/science.aaf6395.