Effector-triggered immunity in oilseed crops is expanded despite the restricted specificity of the receptor ZAR1

Effector-triggered immunity (ETI), mediated by nucleotide-binding leucine-rich repeat immune receptors (NLRs), plays a critical role in protecting plants from pathogens. While the scope of ETI elicited by Pseudomonas syringae type III effectors on Arabidopsis thaliana has been characterized, no equivalent study has been performed on related oilseed crops, limiting our ability to translate fundamental plant immunity research into crop protection strategies. Here, we present a comprehensive screen of the ETI landscapes in Brassicaceous oilseeds Brassica napus (canola) and Camelina sativa (false flax) using 529 P. syringae effectors. We found that 44.6% and 55.4% of the 65 effector families contained alleles that elicited ETI in B. napus and C. sativa, respectively. Mapping ETI-elicitor homologs onto a P. syringae phylogeny revealed that 79% and 88% of strains carry three or more predicted ETI elicitors in B. napus and C. sativa, suggesting a significant ETI load against P. syringae in oilseeds. Oilseed ETI landscapes are expanded relative to A. thaliana, and the number of ETI responses is correlated with the species' NLR repertoire size and ploidy. Interestingly, while the A. thaliana ETI profile is smaller than the two oilseed crops, A. thaliana ETI responses are generally stronger. Further, the A. thaliana ZAR1 NLR has a broader effector recognition spectrum than ZAR1 in B. napus or C. sativa, supporting a role for convergent evolution in expanding immunodiversity. Overall, our findings reveal an expanded functional diversity of crop immune systems compared with a wild relative and highlight both ETI conservation and the divergence of recognition mechanisms.