Contrasting evolutionary rates in lettuce immune receptors reflect functional divergence after subfunctionalisation

Researchers including Hsuan Pai, Toshiyuki Sakai, Sophien Kamoun, and colleagues have published a study in PLOS Genetics examining the evolutionary dynamics of nucleotide-binding leucine-rich repeat (NLR) immune receptors in lettuce, a commercially significant crop in the Asterid lineage.

NLR proteins constitute the principal intracellular immune receptors in plants. Within the NRC (NLR Required for Cell Death) network, NLRs are divided functionally into sensor NLRs — which detect pathogen effectors — and helper NLRs, which transduce the downstream cell-death signal. The study finds that sensor and helper NLRs in lettuce evolve at markedly different rates, and that these contrasting evolutionary patterns reflect genuine functional divergence arising from subfunctionalisation following gene duplication events.

The authors used phylogenomic and population-level sequence analysis to characterise rates of diversifying selection across the two NLR classes in lettuce, comparing intraspecific variation with patterns seen in other Asterid species. Sensor NLRs showed signatures of more rapid, diversifying evolution consistent with an ongoing evolutionary arms race against pathogen effectors. Helper NLRs, constrained by their role as shared signal transducers, evolved more slowly.

The findings contribute to understanding of how immune gene networks are maintained and diversified in crop plants, with potential implications for resistance gene deployment strategies in plant breeding. The work was published in PLOS Genetics.