RLP- and RLK-mediated innate immune responses in Arabidopsis and tomato triggered by pathogen-associated molecular patterns (PAMPs) and a virulence factors (Avrs)

Abstract

Crop plants are continuously threatened by devastating diseases caused by microbial pathogens. Plants possess an innate immune system that is activated after recognition of microbes through general pathogen-associated molecular patterns or specific pathogen-derived avirulence factors. Two types of extracellular plant plasma membrane receptors (receptor-like proteins (RLPs) and receptor-like kinases (RLKs)) perceive PAMPs and Avrs in the intercellular space and initiate an immune response. Both types contain extracellular leucine-rich repeats (eLRR) that monitor the presence of specific pathogen molecules. For RLPs, these eLRRs are anchored in the plasma membrane and carry only a short cytoplasmic domain that lacks obvious signalling motifs. In contrast, RLKs contain a cytoplasmic kinase domain for downstream signalling. Arabidopsis and tomato are well-characterized model plants. The genome sequence of Arabidopsis is available whereas that of tomato will become available within 2-3 years. In tomato, Avr-perceiving RLPs encompass the well-characterized Cladosporium fulvum and the Verticillium dahliae resistance proteins. Tomato RLPs involved in PAMP perception include LeEix proteins that recognize Trichoderma viride. RLKs involved in Avr and PAMP recognition are rice Xa21, recognizing Xanthomonas oryzae, Arabidopsis FLS2 and EFR, recognizing the PAMPs flagellin and EF-Tu, and Arabidopsis BAK1 and ERECTA that are required for resistance against various pathogens. In this proposal we aim to investigate the role of RLPs and RLKs in the perception of microbial pathogens through extracellular PAMPs and Avrs in the plant species tomato and Arabidopsis. Furthermore we want to dissect downstream defense signalling pathways in the two plant species activated upon pathogen perception. The various project partners will study these mechanisms using genetic, proteomics and transcriptomics approaches.