Effector Genomics Accelerates Discovery and Functional Profiling of Potato Disease Resistance and Phytophthora Infestans Avirulence Genes

Abstract

Potato is the world's fourth largest food crop yet it continues to endure late blight, a devastating disease caused by the Irish famine pathogen Phytophthora infestans. Breeding broad-spectrum disease resistance (R) genes into potato (Solanum tuberosum) is the best strategy for genetically managing late blight but current approaches are slow and inefficient. We used a repertoire of effector genes predicted computationally from the P. infestans genome to accelerate the identification, functional characterization, and cloning of potentially broad-spectrum R genes. An initial set of 54 effectors containing a signal peptide and a RXLR motif was profiled for activation of innate immunity (avirulence or Avr activity) on wild Solanum species and tentative Avr candidates were identified. The RXLR effector family IpiO induced hypersensitive responses (HR) in S. stoloniferum, S. papita and the more distantly related S. bulbocastanum, the source of the R gene Rpi-blb1. Genetic studies with S. stoloniferum showed cosegregation of resistance to P. infestans and response to IpiO. Transient co-expression of IpiO with Rpi-blb1 in a heterologous Nicotiana benthamiana system identified IpiO as Avr-blb1. A candidate gene approach led to the rapid cloning of S. stoloniferum Rpi-sto1 and S. papita Rpi-pta1, which are functionally equivalent to Rpi-blb1. Our findings indicate that effector genomics enables discovery and functional profiling of late blight R genes and Avr genes at an unprecedented rate and promises to accelerate the engineering of late blight resistant potato varieties.

Applied Biotechnology to Combat Late Blight in Potato Caused by Phytophthora Infestans

“…When a hypersensitivity reaction occurs in the tobacco leaf the potato R gene recognizes the effector meaning that the interacting Avr gene is identified. A potato carrying that specific R gene is then resistant against this specific pathotype containing the Avr (Vleeshouwers et al 2008).…”

“…When the R gene recognizes the effector, a hypersensitive response (HR) occurs. When three genes are stacked, a functional expression of the R genes can be detected simply by infiltrating the Avr and monitoring for an HR (Vleeshouwers et al 2008). Figure 5 shows the single and multiple resistance genes used with and without a selection marker.…”

Biotech Potatoes in the 21st Century: 20 Years Since the First Biotech Potato

“…1). The discovery of these genes has led to the identification of functionally equivalent variants derived from other wild potato species, such as RB ver , Rpi-sto1, and Rpi-pta1 from S. verrucosum, S. stoloniferum, and S. papita, respectively, which are related to Rpi-blb1 (Liu and Halterman 2006;Vleeshouwers et al 2008). These additional genes provide supplementary genetic variation that could be used in the development of late blight resistant cultivars.…”

Sistemi ortofrutticoli sostenibili

“…I ricercatori, dopo avere lavorato per decine di anni con geni razza-specifici di Solanum demissum, hanno solo recentemente ottenuto la possibilità di coltivazione di patate GM portanti i geni Rpi-blb ed Rpi-blb2, ottenuti da S. bulbocastanum e caratterizzati da resistenza ad un ampio spettro di isolati del patogeno (Vleeshouwers et al, 2008). Gli esempi potrebbero continuare.…”