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Abstract:
Plant cell surface receptors sense microbial pathogens by recognizing microbial structures called pathogen or microbe-associated molecular patterns (PAMPs/MAMPs). There are two major types of plant pattern recognition receptors: (1) plant receptor-like proteins and receptor-like kinases carrying extracellular leucine-rich repeat domains (LRR-RP and LRR-RK) and (2) plant receptor-like proteins and receptor-like kinases carrying extracellular lysin motifs (LysM-RP and LysM-RK). Although many studies focus individually on the signal pathways triggered by different receptor types during the establishment of immunity to microbial infection, the exact overlap and the differences between these pathways remain largely unknown. In this study, Arabidopsis thaliana responses to flg22 and nlp20, via their corresponding receptor types, FLS2 (LRR-RK) and RLP23 (LRR-RP), were compared. Systematic analyses of various plant immune responses revealed that nlp20 triggers only slow and weak early responses such as ROS accumulation and MAPK activation. However, compared to flg22, nlp20 is capable of inducing higher levels of the phytohormones ethylene and salicylic acid. In contrast, flg22 triggers early responses (ROS, MAPKs) faster and stronger, and also causes more extensive transcriptome reprograming. Through a mutational screen focusing on genes with known roles in plant immunity, we found that BIK1 may play different roles in signaling after flg22 and nlp20 treatments. The results present a more complete picture of MAMP-triggered immunity and may lead to the discovery of key components participating in plant immunity.
