The LysM receptor kinase CERK1 mediates bacterial perception in Arabidopsis

Abstract

Plants use pattern recognition receptors (PRRs) to perceive pathogen-associated molecular pattern (PAMPs) and initiate defence responses. PAMP-triggered immunity (PTI) plays an important role in general resistance, and constrains the growth of most microbes on plants. Despite the importance of PRRs in plant immunity, the vast majority of them remain to be identified. We recently showed that the Arabidopsis LysM receptor kinase CERK1 is required not only for chitin signalling and fungal resistance, but plays an essential role in restricting bacterial growth on plants. We proposed that CERK1 may mediate the perception of a bacterial PAMP, or an endogenous plant cell wall component released during infection, through its extracellular carbohydrate-binding LysM-motifs. Here we report reduced activation of a PAMP-induced defence response on plants lacking the CERK1 gene after treatment with crude bacterial extracts. This demonstrates that CERK1 mediates perception of an unknown bacterial PAMP in Arabidopsis.

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Acknowledgements

We are very grateful to Dr. Cyril Zipfel for providing the Col-0 fls2/efr seeds. We thank Dr. Dagmar Hann for many points of discussion and a critical review of the manuscript. The support of the Gatsby Charitable Foundation is gratefully acknowledged.

Figures and Tables

Figure 1 Generation of ROS by Pto DC3000 bacterial extracts in cerk1 mutant plants. (A) ROS burst in Arabidopsis Col-0 fls2/efr and Col-0 fls2/efr/cerk1 plants after treatment with 20 µl/ml of crude bacterial extracts from Pto DC3000. Crude bacterial extracts were prepared by boiling bacterial suspensions for 10 minutes and removing cell debris by centrifugation. Error bars indicate standard error of the mean (SEM). The results shown are representative of four independent experiments. (B) ROS burst in Arabidopsis Col-0 and Col-0 cerk1 plants upon treatment with water, 100 µg/ml chitin, or 30 µl/ml of Pto DC3000 peptidoglycan (PGN). Error bars indicate SEM. Similar results were obtained in two independent experiments.

Figure 2 Schematic representation of microbial perception and signalling through LysM receptor kinases in plants. Plants sense fungi by recognition of chitin oligomers released from fungal cell walls through the LysM receptor proteins CERK1 and CEBiP in Arabidopsis and rice, respectively. The lack of an intracellular signaling domain in the CEBiP protein suggests that the receptor may associate with another protein such as a receptor kinase to transduce the signal. Chitin perception show many similarities with recognition of symbiotic bacteria in leguminous plants. CERK1 is homologous to the legume Nod factor receptors NFR1 and NFR5 mediating perception and signalling of lipo-chitin Nod factors, probably in a heterodimeric complex. The identification of CERK1 as a component required for bacterial immunity suggests that pathogenic bacteria also contain similar chitin-like PAMPs.

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