Abstract
Autophagy plays an important role in plant-pathogen interactions. Several pathogens including viruses induce autophagy in plants, but the underpinning mechanism remains largely unclear. Furthermore, in virus-plant interactions, viral factor(s) that induce autophagy have yet to be identified. Here, we report that the βC1 protein of Cotton leaf curl Multan betasatellite (CLCuMuB) interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPC), a negative autophagic regulator, to induce autophagy in Nicotiana benthamiana CLCuMuB βC1 bound to GAPCs and disrupted the interaction between GAPCs and autophagy-related protein 3 (ATG3). A mutant βC1 protein (βC13A) in which I45, Y48, and I53 were all substituted with Ala (A), had a dramatically reduced binding capacity with GAPCs, failed to disrupt the GAPCs-ATG3 interactions and failed to induce autophagy. Furthermore, mutant virus carrying βC13A showed increased symptoms and viral DNA accumulation associated with decreased autophagy in plants. These results suggest that CLCuMuB βC1 activates autophagy by disrupting GAPCs-ATG3 interactions.
Highlights
Autophagy is a highly conserved mechanism that leads to the degradation and recycling of damaged or unwanted intracellular materials under stress conditions or during specific developmental processes (Klionsky and Codogno, 2013; Yin et al, 2016)
In plants expressing HA-tagged bC1 (HA-bC1), numerous Cyan Fluorescent Protein (CFP)-labeled autophagic bodies were observed compared to plants expressing the HA-tagged C-terminal luciferase (HA-cLUC) control (Figure 1A)
These results indicated that Cotton leaf curl Multan betasatellite (CLCuMuB) bC1 induces autophagy in N. benthamiana
Summary
Autophagy is a highly conserved mechanism that leads to the degradation and recycling of damaged or unwanted intracellular materials under stress conditions or during specific developmental processes (Klionsky and Codogno, 2013; Yin et al, 2016). Three major types of autophagy, that is, macroautophagy, microautopahgy, and chaperone-mediated autophagy, occur in eukaryotic cells (Massey et al, 2004; Klionsky, 2005). Macroautophagy (hereafter referred to as autophagy) is mediated by autophagosome, a de novo–formed double-membrane vesicle. The outer membrane of a mature autophagosome fuses with the lysosome (in mammals) or vacuole (in yeast and plants) to release the sequestered cargo for breakdown by acid hydrolases (Mizushima et al, 2008; Ohsumi, 2001). Increasing evidence shows that viruses manipulate or hijack the autophagy pathway to promote pathogenesis, demonstrating the pivotal role of autophagy in the arms race between hosts and viruses
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