Phytophthora infestansRXLR-WY effector AVR3a associates with a Dynamin-Related Protein involved in endocytosis of a plant pattern recognition receptor

Abstract

Perception of pathogen associated molecular patterns (PAMPs) by cell surface localized pattern recognition receptors (PPRs), activates plant basal defense responses in a process known as PAMP/PRR-triggered immunity (PTI). In turn, pathogens deploy effector proteins that interfere with different steps in PTI signaling. However, our knowledge of PTI suppression by filamentous plant pathogens, i.e. fungi and oomycetes, remains fragmentary. Previous work revealed that BAK1/SERK3, a regulatory receptor of several PRRs, contributes to basal immunity against the Irish potato famine pathogen Phytophthora infestans. Moreover BAK1/SERK3 is required for the cell death induced by P. infestans elicitin INF1, a protein with characteristics of PAMPs. The P. infestans host-translocated RXLR-WY effector AVR3a is known to supress INF1-mediated defense by binding the E3 ligase CMPG1. In contrast, AVR3aKl-Y147del, a deletion mutant of the C-terminal tyrosine of AVR3a, fails to bind CMPG1 and suppress INF1 cell death. Here we studied the extent to which AVR3a and its variants perturb additional BAK1/SERK3 dependent PTI responses using the plant PRR FLAGELLIN SENSING 2 (FLS2). We found that all tested variants of AVR3a, including AVR3aKl-Y147del, suppress early defense responses triggered by the bacterial flagellin-derived peptide flg22 and reduce internalization of activated FLS2 from the plasma membrane without disturbing its nonactivated localization. Consistent with this effect of AVR3a on FLS2 endocytosis, we discovered that AVR3a associates with the Dynamin-Related Protein DRP2, a plant GTPase implicated in receptor-mediated endocytosis. Interestingly, DRP2 is required for ligand-induced FLS2 internalization but does not affect internalization of the growth receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1). Furthermore, overexpression of DRP2 suppressed accumulation of reactive oxygen species triggered by PAMP treatment. We conclude that AVR3a associates with a key cellular trafficking and membrane-remodeling complex involved in immune receptor-mediated endocytosis and signaling. AVR3a is a multifunctional effector that can suppress BAK1/SERK3 mediated immunity through at least two different pathways. AUTHOR SUMMARY Plants have a basal layer of immunity to mount defense responses against invading pathogens; in turn, pathogens deploy effector proteins to subvert plant immunity and manipulate host processes to enable parasitic infection. The Irish potato famine pathogen Phytophthora infestans has a large set of effectors that target multiple host cellular sites. The best-characterized P. infestans effector AVR3a supports enhanced infection and suppresses the cell death induced by the P. infestans protein INF1-elicitin. Previous work demonstrated that the plant immunity co-receptor BAK1/SERK3 contributes to basal immunity to P. infestans and that the RXLR-WY effector of P. infestans suppresses BAK1/SERK3-mediated immunity by binding the E3 ligase protein CMPG1. Here we show that AVR3a suppresses additional defense responses m...

Oomycete Interactions with Plants: Infection Strategies and Resistance Principles

“…As reported earlier, many effector proteins have been shown to suppress PTI responses (23,61,65,82), namely, three tested variants of the P. infestans effector AVR3a suppressed flg22-triggered responses when overexpressed in planta (50). One way to avoid effector overexpression and achieve more targeted application is to deliver effectors via a bacterial pathogen, such as Pseudomonas syringae (61).…”

“…AVR3a was also found to interact with dynamin-related protein 2 (DRP2), a plant GTPase implicated in receptor-mediated endocytosis that, when overexpressed, attenuated PAMP-triggered ROS accumulation (50). It appears from these findings that AVR3a can suppress BAK1/SERK3-mediated immunity via two different methods.…”

A Moving View: Subcellular Trafficking Processes in Pattern Recognition Receptor–Triggered Plant Immunity

“…Consistent with a role for clathrin-mediated endocytosis in trafficking of PRRs, recent work has implicated dynamin GTPases in this process (Figure 1a) (27,126). In Arabidopsis, the closely related DRP2A and DRP2B represent typical dynamin GTPases that scissor and release clathrincoated vesicles (48).…”

“…The flg22 peptide binds to the RLK flagellin-sensing 2 (FLS2), which induces the interaction with BRI1-associated kinase 1 (BAK1), a member of the somatic embryogenesis receptor kinase (SERK) family. This interaction facilitates the flg22-induced activation of the receptor complex to trigger a multilayered defense response (29,30,120,121).…”

“…AVRblb2 targets the papain-like cysteine protease C14 to prevent its secretion into the apoplast, thereby promoting P. infestans virulence (23). Avr3a, another P. infestans-secreted effector, associates with host DRPs to interfere with BAK1-dependent MAMP-triggered defense responses (27). Likewise, PtoDC3000 bacteria secrete HopM1, which localizes to the host TGN to interfere with post-Golgi trafficking mediated by the ARF-GEF family member BIG5, also known as AtMIN7 and BEN1 (103,110,136).…”