Arabidopsis glycosylphosphatidylinositol-anchored protein LLG1 associates with and modulates FLS2 to regulate innate immunity
Friday, 2017/06/02 | 12:40:43
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Qiujing Shen, Gildas Bourdais, Huairong Pan, Silke Robatzek, and Dingzhong Tang
Significance
Recognition of pathogen-associated molecular patterns (PAMPs) by the host immune system is essential for activation of innate immunity in plants and animals. In plants, the receptor kinase FLAGELLIN SENSING 2 (FLS2) recognizes flagellin, a PAMP from bacteria. Here, we found that the glycosylphosphatidylinositol (GPI)-anchored protein LORELEI-LIKE GPI-ANCHORED PROTEIN 1 (LLG1) associates with FLS2 and regulates plant immunity by modulating FLS2 accumulation and signaling. LLG1 functions as a chaperone and coreceptor of FERONIA, a key component in pollen reception and development. This work identifies a shared component for immunity and development, and indicates that modulation of receptor kinases by membrane-localized GPI proteins could be a general mechanism for plants to respond to environmental and developmental cues.
Abstract
Plants detect and respond to pathogen invasion with membrane-localized pattern recognition receptors (PRRs), which recognize pathogen-associated molecular patterns (PAMPs) and activate downstream immune responses. Here we report that Arabidopsis thaliana LORELEI-LIKE GPI-ANCHORED PROTEIN 1 (LLG1), a coreceptor of the receptor-like kinase FERONIA, regulates PRR signaling. In a forward genetic screen for suppressors of enhanced disease resistance 1 (edr1), we identified the point mutation llg1-3, which suppresses edr1 disease resistance but does not affect plant growth and development. The llg1 mutants show enhanced susceptibility to various virulent pathogens, indicating that LLG1 has an important role in plant immunity.
LLG1 constitutively associates with the PAMP receptor FLAGELLIN SENSING 2 (FLS2) and the elongation factor-Tu receptor, and forms a complex with BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 in a ligand-dependent manner, indicating that LLG1 functions as a key component of PAMP-recognition immune complexes. Moreover, LLG1 contributes to accumulation and ligand-induced degradation of FLS2, and is required for downstream innate immunity responses, including ligand-induced phosphorylation of BOTRYTIS-INDUCED KINASE 1 and production of reactive oxygen species.
Taken together, our findings reveal that LLG1 associates with PAMP receptors and modulates their function to regulate disease responses. As LLG1 functions as a coreceptor of FERONIA and plays central roles in plant growth and development, our findings indicate that LLG1 participates in separate pathways, and may suggest a potential connection between development and innate immunity in plants.
See: http://www.pnas.org/content/114/22/5749.abstract.html?etoc PNAS May 30 2017; vol.114; no.22: 5749–5754
Fig. 1. llg1-3 suppresses edr1-mediated resistance to G. cichoracearum. (A) Four-week-old plants were inoculated with G. cichoracearum. Photos were taken of leaves of Col-0, edr1, and edr1 llg1-3 plants at 7 dpi. The llg1-3 mutation suppressed the necrotic and powdery mildew-resistance phenotypes of the edr1 mutant. (Scale bar, 0.25 cm.) (B) Trypan blue staining of leaves after infection with G. cichoracearum at 7 dpi. (Scale bar, 100 μm.) (C) Quantitative analysis of conidiophore formation in Col-0, edr1, and edr1 llg1-3 plants at 5 dpi. Error bars represent SD from three independent experiments (n = 25). (D) Free SA was extracted from uninfected and infected (3 dpi) leaves of 4-wk-old plants with G. cichoracearum. Error bars represent SD from three independent experiments (n = 3). (E) The expression of PR1 was analyzed by quantitative real-time RT-PCR. mRNA was extracted from uninfected and infected (3 dpi) 4-wk-old plants infected with G. cichoracearum. ACTIN2 was used as an internal control. Error bars represent SD from three independent experiments (n = 3). Lowercase letters represent statistically significant differences (P < 0.05, nested ANOVA). |
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