Detection of the Virulent Form of AVR3a from Phytophthora infestans following Artificial Evolution of Potato Resistance Gene R3a

Abstract

Engineering resistance genes to gain effector recognition is emerging as an important step in attaining broad, durable resistance. We engineered potato resistance gene R3a to gain recognition of the virulent AVR3aEM effector form of Phytophthora infestans. Random mutagenesis, gene shuffling and site-directed mutagenesis of R3a were conducted to produce R3a* variants with gain of recognition towards AVR3aEM. Programmed cell death following gain of recognition was enhanced in iterative rounds of artificial evolution and neared levels observed for recognition of AVR3aKI by R3a. We demonstrated that R3a*-mediated recognition responses, like for R3a, are dependent on SGT1 and HSP90. In addition, this gain of response is associated with re-localisation of R3a* variants from the cytoplasm to late endosomes when co-expressed with either AVR3aKI or AVR3aEM a mechanism that was previously only seen for R3a upon co-infiltration with AVR3aKI. Similarly, AVR3aEM specifically re-localised to the same vesicles upon recognition by R3a* variants, but not with R3a. R3a and R3a* provide resistance to P. infestans isolates expressing AVR3aKI but not those homozygous for AVR3aEM.

Comparative Analysis of the Flax Immune Receptors L6 and L7 Suggests an Equilibrium-Based Switch Activation Model

“…Thus, constraints on NLR protein evolution involve a balance between the effectiveness of the resistance response induced by ligand recognition and potential fitness costs due to low-level constitutive signaling in the absence of pathogens. Similar constraints are likely to apply to attempts to engineer immune receptors for enhanced disease resistance in crop plants (Harris et al, 2013;Chapman et al, 2014;Segretin et al, 2014).…”

Oomycete Interactions with Plants: Infection Strategies and Resistance Principles

“…This has caused problems in agricultural contexts where R genes were employed to provide resistance to crop pathogens because the resistance has only been durable if the required Avr gene is essential to the pathogen's success. However, there have been various attempts to improve the chances of durability, namely, stacking multiple R genes within one variety (88) and/or using variety mixtures (89) or multilines (90), as well as engineered R genes with extended recognition spectra (91,92). The use of variety mixtures involves sowing several varieties containing different R genes and different parental backgrounds together in the same field.…”

“…Knowledge of how immune receptors function on a molecular level has already begun to fuel development of engineered receptors that detect a broader range of oomycete effectors (91,92). The function of an R gene and its specificity for a given effector can also be validated via transient coexpression with effectors in plants that do not carry the candidate resistance gene.…”

Recognition of Verticillium effector Ave1 by tomato immune receptor Ve1 mediates Verticillium resistance in diverse plant species

“…Rice SWEET genes are involved in sugar transport and activated by TALEs from the rice bacterial pathogen Xanthomonas oryzae pv. oryzae, presumably facilitating sugar export for bacterial consumption and promoting infection (Boch et al, 2014;Chen, 2014). Characterization of Xanthomonas TALE DNA-binding specificity has uncovered several examples of host target genes that confer bacterial susceptibility as well as target genes present in resistant plants that induce disease resistance (Boch et al, 2014).…”

“…Transfer and artificial evolution of plant immune receptors have successfully been deployed to improve pathogen recognition capacities (Table 1; Farnham and Baulcombe, 2006;Harris et al, 2013;Chapman et al, 2014;Segretin et al, 2014;Giannakopoulou et al, 2015;Helft et al, 2016). These strategies can also be utilized to exploit known immune receptors for engineering disease resistance in crops.…”