An international research group led by Assistant Professor Izumi Yotsui of the Department of Bioscience in the Faculty of Life Sciences at Tokyo University of Agriculture (formerly, Research Fellow of the Plant Proteomics Research Unit, RIKEN Center for Sustainable Resource Science) and Group Leader Hirofumi Nakagami of the Max Planck Institute for Plant Breeding Research have found that LysM receptors in the umbrella liverwort (Marchantia polymorpha, a bryophyte model) are involved in the recognition of fungal and bacterial cell wall components and that pattern-triggered immunity (PTI) contributes to the resistance of M. polymorpha to pathogenic microorganisms. The conservation of the innate immune system in land plants and the existence of a phototropin (PHOT)-mediated PTI regulatory mechanism were demonstrated. The results were published in the August 23 issue of the American scientific journal Current Biology.
Molecular phylogenetic analysis of various plant species with different evolutionary lineages, including M. polymorpha, revealed that this species has one LysM-type receptor-like protein from each of the LYKa, LYKb, LYR, and LYP subgroups. (LysM stands for lysine motif; LYK stands for LysM-receptor-like kinase; LYR stands for LYK-related; and LYP stands for LysM receptor-like protein, membrane-anchored LysM protein.) This suggests that the low genetic redundancy of the system is not only regulated by LysM-type receptor-like proteins in M. polymorpha, but that the plant also acquired genes encoding the four types of LysM-type receptor-like proteins at an early stage of terrestrial evolution.
The research group found that LYKa-type MpLYK1 (where Mp stands for M. polymorpha) and LYR-type MpLYR are required for the induction of immune responses by chitin and peptidoglycan, and MpLYK1 is involved in the resistance of the plant resistance to pathogenic bacteria and filamentous fungi. In contrast, LYP-type MpLYP is not involved in the responses to chitin and peptidoglycan. These findings suggest that the PTI mediated by the LysM-type receptor was already established before the divergence of vascular plants and bryophytes.
Using phosphoproteomic technology, the researchers comprehensively searched for a group of PTI-related proteins downstream of the LysM-type receptor in M. polymorpha. They found that phosphorylation of MpLyR and MpLyK1 (which can function as a chitin receptor or co-receptor), changed with chitin treatment; receptor-like cytoplasmic kinase (RLCK), which regulates PTI in the plant Arabidopsis thaliana; and mitogen-activated protein kinase (MAPK), MAPK kinase (MAPKK), and MAPK kinase kinase (MAPKKK), which are homologs (i.e., genes with similar sequences derived from a common ancestor) in M. polymorpha. They also found that the contribution of several factors to PTI has not been reported, including PHOT, a blue-light receptor that exists in a wide range of organisms (from algae to higher plants).
An analysis using mutants of M. polymorpha revealed that MpPHOT is involved in restoring the steady state of the plant's immune system, which it performs by suppressing the expression of a group of genes that are transcriptionally induced by microbe-associated molecular patterns. This indicates the conservation of the innate immune system and the existence of a PHOT-mediated PTI regulatory mechanism in land plants.
These results are expected to help in understanding the origin, conservation, and diversity of the plant immune system and contribute to the development of universal disease resistance technologies that can be used in many plant species.
Yotsui commented, "It took us a long time to create transgenic plants to analyze the immune response. We needed to uniformly align the growth stages of the transgenic plants for comparative analysis, and when many transgenic plants were needed for comparison, it was difficult to culture them. In the future, we believe that if the system is conserved among plant species, it could contribute to the development of a universal disease resistance technology that can be used in many plant species and to the future breeding of disease-resistant crop species."
Journal Information
Publication: Current Biology
Title: LysM-mediated signaling in Marchantia polymorpha highlights the conservation of pattern-triggered immunity in land plants
DOI: 10.1016/j.cub.2023.07.068
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.