The Irish potato famine pathogen subverts host vesicle trafficking to channel starvation-induced autophagy to the pathogen interface

Abstract

Eukaryotic cells deploy autophagy to eliminate invading microbes. In turn, pathogens have evolved 22 effector proteins to counteract antimicrobial autophagy. How and why adapted pathogens co-opt 23 autophagy for their own benefit is poorly understood. The Irish famine pathogen Phythophthora 24 infestans secretes the effector protein PexRD54 that selectively activates an unknown plant 25 autophagy pathway, while antagonizing antimicrobial autophagy. Here we show that PexRD54 26 induces autophagosome formation by bridging small GTPase Rab8a-decorated vesicles with 27 autophagic compartments labelled by the core autophagy protein ATG8CL. Rab8a is required for 28 pathogen-triggered and starvation-induced but not antimicrobial autophagy, revealing that specific 29 trafficking pathways underpin selective autophagy. We discovered that Rab8a contributes to basal 30 immunity against P. infestans, but PexRD54 diverts a sub-population of Rab8a vesicles to lipid 31 droplets that associate with autophagosomes. These are then diverted towards pathogen feeding 32 structures that are accommodated within the host cells. We propose that PexRD54 mimics starvation-33 induced autophagy by channeling host endomembrane trafficking towards the pathogen interface 34 possibly to acquire nutrients. This work reveals that effectors can interconnect independent host 35 compartments to stimulate complex cellular processes that benefit the pathogen. Graphical abstract: 37 38 39 40 41 42 43 44 45 Introduction: 46 47Autophagy is a conserved eukaryotic cellular process that mediates the lysosomal degradation and 48 relocation of cellular cargoes within double-membraned vesicles called autophagosomes (He and 49 Klionsky, 2009; Leidal et al., 2020). Although autophagy is historically considered to be a bulk 50 catabolic pathway tasked with maintaining cellular homeostasis under normal or stress conditions, it 51 is now clear that autophagy can be highly selective in cargo choice (Zaffagnini and Martens, 2016). 52Autophagic cargoes are typically captured during autophagosome formation, a complex process that 53 is regulated by the concerted action of a set of conserved autophagy related proteins (ATG) as well 54 as specialized autophagy adaptors and cargo receptors (Mizushima et al., 2011). These captured 55 cargoes are sorted within the autophagosome during maturation of the isolation membrane (also 56 known as the phagophore) via the specific interactions between cargo receptors and a lipidated form 57 of ATG8, which decorates the phagophore to serve as a docking platform for cargo receptors 58 (Ryabovol and Minibayeva, 2016; Slobodkin and Elazar, 2013). 60The source of the phagophore is still under debate, but its primary source is considered to be the 61 endoplasmic reticulum (ER) (Bernard and Klionsky, 2013; Hamasaki et al., 2013). As the cargo is 62 being captured, the phagophore undergoes massive expansion and finally gets sealed to form a 63 mature autophagosome. Therefore, formation of the autophagosome requires additional lipid supplies 64...

Host-interactor screens ofPhytophthora infestansRXLR proteins reveal vesicle trafficking as a major effector-targeted process

“…PexRD54 was also recently proposed to connect small GTPase Rab8a vesicles with the autophagy machinery to stimulate formation of autophagosomes at the pathogen interface (Pandey et al, 2020). In our host-interactor screen, we found that ten effector families associated with 32 proteins implicated in vesicle mediated transport ( Figure 2, Figure S3, Table S2).…”

“…binding (Pandey et al, 2020). The PexRD54 work illustrates the importance of replication and follow-up experiments to the coIP/MS.…”

“…These findings, along with related cell biology and biochemical studies, indicate that P. infestans massively reprograms host membrane trafficking during infection (Du et al, 2015;Tomczynska et al, 2018). Membrane trafficking perturbations of haustoriated cells include the rerouting to the haustorial interface of components of the endocytic pathways (Lu et al, 2012;Bozkurt et al, 2015), autophagy machinery (Dagdas et al, 2018;Pandey et al, 2020) and chloroplasts (Toufexi et al, 2019).…”

“…These 16 "usual suspect" interactors overlap with the list previously reported by Petre et al (2015) Five host interactors of P. infestans RXLR effectors in our interactome matrix have been previously validated (Table S1). The cysteine protease RD21a (C14) associates with members of the AVRblb2 family (Bozkurt et al, 2011;Wang et al, 2015), the BSU1-like serine/threonine protein phosphatases BSL1 and BSL3 associate with members of the AVR2 family (Saunders et al, 2012), dynamin 2B associates with the AVR3a family (Chaparro-Garcia et al, 2015) and Ras-related protein RabE1c (also known as Rab8a) associates with PexRD54 (Pandey et al, 2020) (Table S1, Figure 1C). These validated host interactors associated with anywhere from 1 to 5 effector families in our experiments (Table S1).…”

Emerging Roles of the Selective Autophagy in Plant Immunity and Stress Tolerance

“…However, the reason behind this is not understood. Recently, it has been revealed that PexRD54 imitates starvation conditions and serves as a receptor for recruiting the small GTPase Rab8a with a role in basal resistance against P. infestans , and the lipid droplets (LDs) associated with Rab8a to form a distinct LDs-Rab8a-PexRD54-ATG8CL autophagosomes [ 113 ] ( Figure 2 ). As a result, the Rab8a is trapped inside the autophagosomes and the Rab8a-mediated basal immunity is pacified [ 113 ] ( Figure 2 ).…”