An Aphid Protein Interferes with Plant endomembrane Trafficking Machinery to Promote Aphid Survival and Plant Growth

Aphids deplete their host plants of amino acids and other essential nutrients by feeding on phloem sap. Autophagy, a conserved process across eukaryotes, maintains cellular homeostasis during starvation and environmental stress by recycling damaged or excess cellular components. Here, we identified and characterized a previously uninvestigated aphid salivary protein, termed Aphid Autophagy Related Factor 1 (AAF1), that is secreted into plant cells and manipulates plant physiology in a manner that benefits the aphid. We show that AAF1 interacts with four known or putative host autophagy related proteins: RABD1 and RABD2a (plant homologs of Ypt1/RAB1), ATG8, a ubiquitin like protein required for autophagosome formation, and PI3PT, a previously uncharacterized ER localized putative lipid binding or lipid transfer protein annotated as a phosphoinositide 3 phosphate transfer protein. We further demonstrate that the RAB binding domain of AAF1 and its interaction with RABD2a may be specifically required for AAF1 function. In addition, we identified unique, highly mobile compartments containing interacting AAF1 and RABD2a that are associated with the endoplasmic reticulum (ER) and dynamically traffic with autophagosomes. We propose that these compartments may be derived from endosomes or endosome to ER contact sites (EERCSs) and serve as platforms for autophagosome trafficking and/or biogenesis. We further propose that AAF1, RABD2a, and PI3PT function together to regulate the formation or function of these compartments, thereby supporting autophagosome formation and trafficking. Finally, we show that stable expression of AAF1 in plants enhances growth and biomass in an autophagy dependent manner.