Citrus relatives exhibit natural variation in perception and response magnitude to microbial features

Although much is known about the responses of model plants to microbial features, we still lack an understanding of the extent of variation in immune perception across members of a plant family. In this work, we analyzed immune responses in Citrus and wild relatives, surveying 86 Rutaceae genotypes with differing leaf morphologies and disease resistances. We found that responses to microbial features vary both within and between members. Species in two subtribes, the Balsamocitrinae and Clauseninae, can recognize all tested microbial features (flg22, csp22, chitin), including one from Candidatus Liberibacter species (csp22 C Las ), the bacterium associated with citrus greening disease aka Huanglongbing. Chitin perception is widespread among Rutaceae genotypes. We were able to characterize a homolog of the Arabidopsis LYK5 receptor in ‘Tango’ mandarin that is capable of conferring chitin perception. These findings shed light onto the diversity of perception of microbial features and highlight genotypes capable of recognizing polymorphic microbial features whose receptors have promise for transfer to susceptible varieties. our utilizes a different LysM receptor (CEBiP) along with the CERK1 co-receptor for chitin (Kaku et al. 2006, Lee et al. 2014, Shimizu et al. 2010). Cotton, a dicot, has a wall-associated kinase that interacts with LYK5 and CERK1 to promote chitin-induced dimerization (Wang et al. 2020). These results are consistent with an ancient acquisition of chitin perception in dicots, which may explain why a vast majority of the Rutaceae genotypes we evaluated are capable of producing an immune response to chitin. For MAMPs that can be recognized by a broad range of species, identifying receptors based on homology is still a useful tactic.