A Nature paper from Jijie Chai’s Group, School of Life Sciences, Tsinghua University, revealing a new recognition mechanism for peptide hormones by a plant receptor

2019-07-12 11:20:45

A Nature paper entitled “Mechanisms of RALF peptide perception by a heterotypic receptor complex” from Jijie Chai’s group, School of Life Sciences, Tsinghua University and their cooperators Cyril Zipfel’s group, The Sainsbury Laboratory, UK, was published on 10 July 2019.

FERONIA (FER) in the model plant Arabidopsis thaliana is a founding member of the receptor kinase (RK) CrRLK1L subfamily, and has crucial roles in plant growth and development, reproduction and immunity. The peptide hormone RAPID ALKALINIZATION FACTORS (RALFs) and the glycosyl-phosphatidyl-inositol (GPI)-anchored proteins (GAPs) LORELEI (LRE) and its homologs LLG1/2/3 are essential for FER-mediated signaling and were proposed to work together as part of a receptor complex. For example, RALF23 was shown to interact with FER and inhibit plant immunity induced by pathogen-associated molecular patterns (Stegmann M et al, Science 2017). How RALFs are recognized by FER, however, remained elusive. In this study, Jijie Chai's group solved several crystal structures including apo-FER, apo-LLG1 and the RALF23-LLG2-FER complex. Supported by biochemical and functional data, the structures showed that LLG1/2/3 bind to RALF23 and thereby the peptide functions to nucleate a FER-LLG-RALF23 complex. Structural comparison revealed the mechanism governing specific recognition of RALF23 by LLGs. Based on the structures, they also identified several RALFs with binding properties similar to that of RALF23 in vitro. The study revealed a novel heterotypic activation pattern of RKs, providing a new paradigm for the understanding of this large family of receptors that control multiple key aspects of plants’ life. The identification of LLGs as receptors of RALF23 assigned a function of GAPs with about 250 members in Arabidopsis. Recognition of multiple RALFs could provide an explanation for the multitasking roles of FER in plant biology.

Figure. Overall structure of FER-RALF23-LLG2

The PhD candidate Yu Xiao from Tsinghua University, Dr Martin Stegmann from The Sainsbury Laboratory and the associate research fellow Dr Zhifu Han from Tsinghua University are co-first authors of the paper. Prof. Jijie Chai from Tsinghua university and Prof. Cyril Zipfel from The Sainsbury Laboratory and the University of Zürich are co-corresponding authors. Dr Thomas A. DeFalco from The Sainsbury Laboratory and the University of Zürich, Katarzyna Parys, and Dr Youssef Belkhadir from the Gregor Mendel Institute, and Li Xu from Tsinghua University also participated in this study. This research was funded by the National Natural Science Foundation of China, the Ministry of Science and Technology, Tsinghua-Peking Joint Center for Life Sciences, and the Advanced Innovation Center of Structural Biology in Beijing, the European Research Council, the Gatsby Charitable Foundation, and the University of Zürich.