Autophagic degradation of the Cucumber mosaic virus virulence factor 2b balances antiviral RNA silencing with proviral plant fitness and virus seed transmission

Abstract

22Autophagy is a conserved intracellular degradation pathway that has recently emerged as an 23 integral part of plant responses to virus infection. The elucidated mechanisms of autophagy 24 range from the selective degradation of viral components to a more general attenuation of 25 disease symptoms. In addition, several viruses are able to manipulate the autophagy machinery 26 and counteract autophagy-dependent resistance. Despite these findings, the complex interplay 27 of autophagy activities, viral pathogenicity factors, and host defence pathways in disease 28 development remains poorly understood. In the current study, we analysed the interaction 29 between autophagy and Cucumber mosaic virus (CMV) in Arabidopsis thaliana. We show that 30 autophagy is induced during CMV infection and promotes the turnover of the major CMV 31 virulence protein and RNA silencing suppressor 2b. Intriguingly, 2b itself dampens plant 32 autophagy. In accordance with 2b degradation, we found that autophagy provides resistance 33 against CMV by reducing viral RNA accumulation in an RNA silencing-dependent manner. 34Moreover, autophagy and RNA silencing pathways contribute to plant longevity and fecundity 35 of CMV infected plants in an additive manner, uncoupling it from resistance. In addition to 36 reduced fecundity, autophagy-deficient plants also failed to support seed transmission of the 37 virus. We propose that autophagy attenuates CMV virulence via 2b degradation and thereby 38 increases both plant and virus fitness with a trade-off penalty arising from increased RNA 39 silencing-mediated resistance. 40 41 42 Author summary 43The capacity of plants to fight pathogenic viruses in order to survive and minimize damage 44 relies on profound cellular reprogramming events. These include the synthesis of new as well 45as the degradation of pre-existing cellular components, together shifting cellular homeostasis 46

Turnip crinkle virus targets host ATG8 proteins to attenuate antiviral autophagy

“…The copyright holder for this preprint this version posted March 29, 2021. ; https://doi.org/10.1101/2021.03.28.437395 doi: bioRxiv preprint counter-defence mechanism by the virus, putting both under different selective pressures. Many studies have established that autophagy has evolved as a frontrunner in plant virus defence and tolerance, with a broad-range of mechanisms deduced collectively for Caulimoviruses (Hafren et al, 2017), Potyviruses (Hafren et al, 2018;Li et al, 2018), Hordeiviruses (Yang et al, 2018), Tenuiviruses (Fu et al, 2018), Geminiviruses (Haxim et al, 2017;Ismayil et al, 2020) and Cucumoviruses (Shukla et al, 2020). Given the important role of autophagy in maintaining plant homeostasis, cellular quality control and stress adaptation, it is understandable that autophagy is a key contributor in virus defence.…”

“…Mutants atg5-1, nbr1, ago1-27, dcl2 dcl4, atg7 dcl2 dcl4 , and the GFP-ATG8a and NBR1-GFP transgenic line have been described previously (Hafren et al, 2018). The ago1-27 atg5-1 double mutant was generated by crossing, as described in (Shukla et al, 2020). The transgenic line expressing P38 tag-RFP (pGWB660) was obtained by floral dip transformation of the GFP-ATG8a line.…”

“…Biomass loss can be a measure of disease severity or virulence upon virus infection. Previously, we showed that the core autophagy genes ATG5 and ATG7 are important for reducing disease severity in CaMV, TuMV and CMV infected plants, while the selective autophagy cargo receptor NBR1 had no significant effect (Hafren et al, 2017;Hafren et al, 2018;Shukla et al, 2020). To address whether functional autophagy affects TCV disease development in a similar manner, we monitored infection development in loss of function mutants atg5 and nbr1 compared to the Col-0 wild-type (WT).…”

“…In recent years, autophagy has been implicated plant-pathogen interactions including diseases caused by viruses, bacteria, fungi and oomycetes (Hofius et al, 2017; Kushwaha et al, 2019; Leary et al, 2019). In plant-virus interactions, a plethora of examples have demonstrated that autophagy can have both anti-viral and pro-viral activities (Fu et al, 2018; Hafren et al, 2017; Hafren et al, 2018; Haxim et al, 2017; Ismayil et al, 2020; Li et al, 2018; Li et al, 2020b; Shukla et al, 2020; Yang et al, 2018). For instance, autophagy targets viral components and contributes to plant resistance via the cargo receptor NEIGHBOUR OF BRCA1 (NBR1) that mediates xenophagic degradation of Cauliflower mosaic virus (CaMV) viral particles (Hafren et al, 2017).…”

“…The polerovirus VSR P0 targets the RISC component AGO1 and triggers its ubiquitination and autophagic degradation (Derrien et al, 2012). On the contrary, autophagy favors plant defense and targets VSRs such as the potyviral helper-component proteinase (HCpro), cucumoviral 2b, and geminiviral bC1 for degradation (Hafren et al, 2018; Haxim et al, 2017; Ismayil et al, 2020; Nakahara et al, 2012; Shukla et al, 2020). At the same time, VSRs are commonly strong virulence factors and their autophagic degradation especially at later stages of infection should contribute to disease attenuation in favor of both the plant and virus.…”