Exploiting Knowledge of Pathogen Effectors to Enhance Late Blight Resistance in Potato

Abstract

Late blight disease of potato, caused by Phytophthora infestans, is the most serious disease of this crop on a global scale and is thus a threat to food security. Use of resistant potato cultivars to prevent late blight does not have a very successful history, as P. infestans genotypes have overcome the deployed resistances. Thus, there is a need to identify more durable resistances, or identify and develop novel forms of resistance that exploit vulnerabilities in the biology of P. infestans. Application of molecular biology tools in P. infestans research has recently culminated in the identification of several avirulence effectors matching specific resistances in potato, the sequencing of the P. infestans genome and identification of hundreds of candidate translocated pathogen 'RXLR' effector proteins that may promote disease progression. Strategies for prioritising these effectors for further research are revealing those that are highly expressed during infection, difficult for the pathogen to alter rapidly, essential for P. infestans pathogenesis and recognized by resistant accessions of Solanum spp. These effector characteristics are being used to identify and characterise resistances from Solanum germplasm that may prove more durable. In addition to RXLR effectors, P. infestans also produces a broad spectrum of additional secreted proteins. These are exposed to plant cells and may potentially act to trigger resistance, either as broad spectrum pathogen-associated molecular patterns or as specific effectors of resistance. Alternatively, conserved secreted proteins may be attractive targets for novel agrichemical development. We have silenced a diverse selection of these candidate secreted proteins in P. infestans and demonstrated their effects on late blight disease development. Results from these studies are aiding a deeper understanding of P. infestans disease development and identifying potential pathogen weaknesses for exploitation in future control measures.

A Phytophthora effector protein promotes symplastic cell‐to‐cell trafficking by physical interaction with plasmodesmata‐localised callose synthases

“…Trafficking through PD suggests that some effectors might prepare host cells for an upcoming invasion (Khang et al, 2010). One of the best analysed groups of effectors of filamentous pathogens are the RxLR effectors of oomycetes (Whisson et al, 2011;Anderson et al, 2015). This class of organisms includes downy mildews and the genus Phytophthora, with P. infestans responsible for the late blight disease of potato and tomato and P. sojae causing stem and root rot in soybeans.…”

Phosphite-induced changes of the transcriptome and secretome in Solanum tuberosum leading to resistance against Phytophthora infestans

“…The initial biotrophic phase leads into a necrotrophic phase characterized by colonization and sporulation on the leaf tissue which in turn gives rise to zoospores for a new cycle of infection [ 1 ]. Although there is naturally occurring resistance in wild potato relatives, sustainable resistance has been difficult to achieve at least partly due to rapid adaptation of the oomycete [ 2 , 3 ]. The predominant method to control for late blight disease is through frequent use of fungicides.…”

Can silencing of transposons contribute to variation in effector gene expression inPhytophthora infestans?

“… 3 In comparison, pathogens have evolved various ways to evade detection by these resistance proteins, such as variations in sequence, gene loss, or transcriptional inactivation (reviewed in refs. 4 and 5 ). Effectors are thus considered to define the host range of a pathogen, by adapting to specific host target proteins.…”

“…PiAvr2 , together with PiAvr4 , PiAvrBlb1 , and PiAvrBlb2 (reviewed in ref. 5 ) are found within 2 kb of transposon-derived sequences.…”