Abstract
The plant immune receptor FLAGELLIN SENSING 2 (FLS2) is present at the plasma membrane and is internalized following activation of its ligand flagellin (flg22). We show that ENDOSOMAL SORTING COMPLEX REQUIRED FOR TRANSPORT (ESCRT)-I subunits play roles in FLS2 endocytosis in Arabidopsis. VPS37-1 co-localizes with FLS2 at endosomes and immunoprecipitates with the receptor upon flg22 elicitation. Vps37-1 mutants are reduced in flg22-induced FLS2 endosomes but not in endosomes labeled by Rab5 GTPases suggesting a defect in FLS2 trafficking rather than formation of endosomes. FLS2 localizes to the lumen of multivesicular bodies, but this is altered in vps37-1 mutants indicating compromised endosomal sorting of FLS2 by ESCRT-I loss-of-function. VPS37-1 and VPS28-2 are critical for immunity against bacterial infection through a role in stomatal closure. Our findings identify that VPS37-1, and likewise VPS28-2, regulate late FLS2 endosomal sorting and reveals that ESCRT-I is critical for flg22-activated stomatal defenses involved in plant immunity.
Highlights
The metazoan and plant immune systems deploy pattern recognition receptors (PRRs) at the cell surface to sense a wide range of potentially pathogenic microbes through the presence of distinct pathogen-associated molecular patterns (PAMPs), conserved molecules displayed by microbes [1]
Following uptake from the plasma membrane, endocytosed FLAGELLIN SENSING 2 (FLS2) arrives at the SYP61-positive trans-Golgi network (TGN)/ early endosomal (EE) compartment and the activated receptor is delivered to late endosomal compartments/multivesicular bodies (LE/MVB), from where it can be sorted for degradation [3,4]
FLS2 is known to shuttle between the plasma membrane and endosomal compartments but enters the late endosomal trafficking pathway upon ligand-dependent activation
Summary
The metazoan and plant immune systems deploy pattern recognition receptors (PRRs) at the cell surface to sense a wide range of potentially pathogenic microbes through the presence of distinct pathogen-associated molecular patterns (PAMPs), conserved molecules displayed by microbes [1]. FLAGELLIN SENSING 2 (FLS2) encodes the PRR that perceives the bacterial PAMP flagellin (flg22) and is required for immunity against bacteria [1]. Upon binding of flg to the receptor, FLS2 signaling pathways are activated by complex formation and phosphorylation between FLS2 and BRASSINOSTEROID INSENSITIVE 1 (BRI1)ASSOCIATED KINASE 1 (BAK1) [2]. Endosomal sorting of vacuolar cargo involves the delivery of cargo to the LE/MVBs, and more precisely to the luminal vesicles of these compartments. This has been demonstrated in plants for only few plasma membrane proteins: PINFORMED 1 (PIN1), REQUIRES HIGH BORON 1 (BOR1), and BRI1 [5,6,7,8,9,10]
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