Plant UVRAG interacts with ATG14 to regulate autophagosome maturation and geminivirus infection.

Autophagy is an essential degradation pathway that assists eukaryote survival under multiple stress conditions. Autophagosomes engulfing cargoes accomplish degradation only when they have matured through fusing with lysosomes or vacuoles. However, the molecular machinery mediating autophagosome maturation in plants remains unknown. Using combined approaches of mass spectrometry, biochemistry, reverse genetics and microscopy, we uncover that, UVRAG, a subunit of the class III phosphatidylinositol 3-kinase complexes in Nicotiana benthamiana, plays an essential role in autophagsome maturation via ATG14-assisted recruitment to autophagosomes and facilitating RAB7 activation. An interaction between N. benthamiana UVRAG and ATG14 is observed in vitro and in vivo, which strikingly differs from their mutually exclusive appearance in different PI3KC3 complexes in yeast and mammals. This interaction increases localization of UVRAG on autophagosomes and enables convergence of autophagic and late endosomal structures, where they contribute to fusions between these two types of organelles by recruiting the essential membrane fusion factors RAB7 GTPase and HOPS complex. In addition, we uncover a joint contribution of ATG14 and UVRAG to geminiviral infection, beyond autophagy. Our study provides insights into mechanisms of autophagosome maturation in plants and expands understanding of organizations and roles of the PI3KC3 complexes. [Abstract copyright: This article is protected by copyright. All rights reserved.]