The Valsa Mali effector Vm1G-1794 protects the aggregated MdEF-Tu from autophagic degradation to promote infection in apple

ABSTRACTMacroautophagy/autophagy is a conserved degradation pathway in eukaryotes that is required for recycling unwanted intracellular components, maintaining homeostasis, and coping with biotic and abiotic stresses. Pathogens have evolved to subvert autophagic machinery by secreting host cell-entering effector proteins. Here, we provided evidence that an apple autophagy-related gene MdATG8i, activated autophagy and contributed to resistance against Valsa canker caused by Valsa Mali (Vm) when being overexpressed in apple. MdATG8i interacted with a plastid elongation factor Tu (MdEF-Tu) which became insoluble and aggregated during Vm infection and was degraded through the autophagy pathway. Intriguingly, we identified a highly-induced effector secreted from Vm, Vm1G-1794, which competitively interacted with MdATG8i, suppressed autophagy, and depleted MdEF-Tu out of MdATG8i complexes. The formation of stable MdEF-Tu aggregates caused by Vm1G-1794 promoted the susceptibility of apple to Vm. Overall, our study demonstrated that MdATG8i contributed to Vm resistance by targeting and degrading MdEF-Tu, and Vm1G-1794 competed with MdEF-Tu to target MdATG8i and prevent MdEF-Tu degradation, thus favoring infection.Abbreviations: 35S: cauliflower mosaic virus 35S promoter; AIM: ATG8-interacting motif; ATG8–PE: ATG8 conjugated with phosphatidylethanolamine; BiFC: biomolecular fluorescence complementation; Con A: concanamycin A; Co-IP: co-immunoprecipitation; DEPs: differentially expressed proteins; DMSO: dimethyl sulfoxide; GFP: green fluorescent protein; hpt: hours post-treatment; LCI: luciferase complementation imaging; MdATG8i: autophagy-related protein 8i in Malus domestica; MDC: monodansylcadaverine; MdEF-Tu: elongation factor Tu in Malus domestica; MdNBR1: neighbor of BRCA1 in Malus domestica; N. benthamiana: Nicotiana benthamiana; OE: overexpression; PAMP: pathogen-associated molecular pattern; PTI: pattern-triggered immunity; qRT-PCR: quantitative reverse transcription PCR; RFP: red fluorescent protein; RNAi: RNA interference; ROS: reactive oxygen species; Ub: ubiquitin; V. Mali: Valsa Mali; WT: wild-type plant; YFP: yellow fluorescent proteinKEYWORDS: Appleautophagyeffectorubiquitinationvalsa Mali AcknowledgmentsWe thank Dr. Chunlei Tang (Northwest A&F University) for providing pSUC2 vector, Prof. Yu Du (Northwest A&F University) for fruitful discussions. We are grateful to Dr. Yangyang Yuan and Minrong Luo (Horticulture Science Research Center, Northwest A&F University, Yangling, China) for providing professional technical assistance.Disclosure statementThe authors declare that they have no competing interests.Data availabilityData supporting the major findings of this work are available within the manuscript and its Supplementary Information files. Any other supporting data is available from the corresponding authors upon request. Source data are provided with this paper.Supplementary MaterialSupplemental data for this article can be accessed online at https://doi.org/10.1080/15548627.2022.2153573Additional informationFundingNational Key Research and Development Program of China (2018YFD1000300, C.L., F.M.)National Natural Science Foundation of China (32172529, C.L.)China Agriculture Research System of MOF and MARA (CARS-27, F.M.)Major Science and Technology Projects in Shaanxi Province (2020zdzx03-01-01, C.L.)Fundamental Research Funds for the Central Universities. (2452019050, C.L.), China Postdoctoral Science Foundation (2017M610657, 2018T111108, C.L; Agriculture Research System of China