Symbiotic root infections inMedicago truncatularequire remorin-mediated receptor stabilization in membrane nanodomains

Abstract

Plant cell infection is tightly controlled by cell surface receptor-like kinases (RLKs)Alike other RLKs the Medicago truncatula entry receptor LYK3 laterally segregates into membrane nanodomains in a stimulus-dependent manner. Although nanodomain localization arises as a generic feature of plant membrane proteins, molecular mechanisms underlying such dynamic transitions and their functional relevance remained poorly understood. Here, we demonstrate that actin and the flotillin protein FLOT4 form the primary and indispensable core of a specific nanodomain. Infection-dependent induction of the remorin protein and secondary molecular scaffold SYMREM1 results in subsequent recruitment of ligand-activated LYK3 and its stabilization within these membrane subcompartments. Reciprocally, the majority of this LYK3 receptor pool is destabilized at the plasma membrane and undergoes rapid endocytosis in symrem1 mutants upon rhizobial inoculation resulting in premature abortion of host cell infections.These data reveal that receptor recruitment into nanodomains is indispensable for their function during host cell infection.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/179036 doi: bioRxiv preprint first posted online Dec. 31, 2017; 3 SIGNIFICANCE STATEMENT:Pattern recognition receptors control the cellular entry of pathogenic as well as symbiotic microbes. While ligand-induced changes in receptor mobility at the plasma membrane and their localization in membrane nanodomains appears as a general feature, the molecular mechanism and the biological relevance of this phenomenon remained unknown. Here, we show that immobilization of the symbiotic cell entry receptor LYK3 in nanodomains requires the presence of actin and the two molecular scaffold proteins FLOT4 and SYMREM1. While FLOT4 forms the initial core structure, infection-induced expression and subsequent physical interaction of SYMREM1 with LYK3 stabilizes the activated receptors in membrane nanodomains. This recruitment prevents its stimulusdependent endocytosis and ensures progression of the primary infection thread into root cortical cells.All rights reserved. No reuse allowed without permission.

The crossroads of receptor‐mediated signaling and endocytosis in plants

“…This localization pattern has been reported for the Medicago truncatula receptor LYSINE MOTIF KINASE3 (LYK3) (Liang et al 2018), the Arabidopsis receptors BRI1, FLS2 and members of the SOMATIC EMBROGENESIS RECEPTOR KINASE (SERK) family of coreceptors (Hutten et al 2017;). Furthermore, proteins, such as remorin (REM) and flotillin (FLOT), thought to function in the receptor-complex assembly and to mark lipid MDs in the PM, colocalize with RLKs Liang et al 2018).…”

The bacterial quorum sensing signal DSF hijacksArabidopsis thalianasterol biosynthesis to suppress plant innate immunity

“…In addition to the endocytic internalization that removes material from the plasma membrane, the lateral nano-clustering of plasma membrane-bound receptors through multivalent interactions is well-known to mediate diverse signal transduction mechanisms during host-pathogen interactions (27; 28). The self- or hetero-oligomerization of surface receptors are critical for receptor activation, signal amplification, and signal transduction in both plants and human, such as the brassinosteroid receptor BRI1 (29), chitin receptor At CERK1 (30), EGF receptor (31, 32) or insulin receptor IR/IGFR (33).…”

“…Increasing evidence supports the roles of membrane microdomains in host innate immunity by regulating surface receptor dynamics in and out of microdomains on plasma membrane upon ligand-recognition, subsequent receptor interactions, and innate immunity activation (27; 96; 97). For instance, disruption of PM continuity is competent enough to abolish the signaling carried out by multiple PM receptors (BRI1, FLS2, EGFR) (28, 98).…”

Remorin interacting with PCaP1 impairs Turnip mosaic virus intercellular movement but is antagonised by VPg

“…The homeostasis of NDs is very important for the resident molecules or complexes to carry out their biological functions. REMs and flotillins are important scaffold proteins of NDs (Mongrand et al, 2010;Jarsch et al, 2014;Ott, 2017;Gronnier et al, 2018;Liang et al, 2018), while the actin cytoskeleton is involved in ND assembly and stabilisation (Szymanski et al, 2015;Ott, 2017;Liang et al, 2018;Yan et al, 2019). Therefore, REMs, flotillins and actin filaments jointly coordinate ND homeostasis.…”

“…The actin filament-severing activity of PCaP1 is selectively employed by TuMV via interaction with P3N-PIPO, which alters the localisation of PCaP1 on NDs and releases PCaP1 from the restriction of REM1.2 or PtdInsPs to sever the actin filaments in close proximity to or in PD. Disruption of the actin filaments abrogates the homeostasis of PD NDs and redistributes REM1.2 from DRMs to DSMs (Szymanski et al, 2015;Ott, 2017;Liang et al, 2018). The mislocalised REM1.2 is destined to be degraded by interaction with VPg via both UPS and autophagy pathways, a counteractive strategy against host defence employed by potyviruses.…”