SsATG8 and SsNBR1 mediated-autophagy is required for fungal development, proteasomal stress response and virulence in Sclerotinia sclerotiorum.

• This study identified a autophagy receptor NBR1 in S. sclerotiorum and confirmed that SsNBR1 physically interact with SsATG8 both in vivo and in vitro. • This study experimentally characterized the biological roles of SsATG8 and its receptor SsNBR1 in S. sclerotiorum , and provided evidences that SsATG8- and SsNBR1-dependent autophagy is critical for the fungal development and pathogenesis. • This study revealed that SsATG8- and SsNBR1-mediate autophagy regulate proteasomal stress responses. • This study identified two docking sites, LDS and UDS of ATG8, which may responsible for binding to various autophagic adaptors and receptors, required for autophagy and pathogenesis S. sclerotiorum. Autophagy plays vital roles in the interaction between the necrotrophic fungal pathogen Sclerotinia sclerotiorum and its hosts. However, so far, only little is known about the impacts of autophagy machinery in S. sclerotiorum per se on the fungal morphogenesis and pathogenesis. Here, through functional genomic approaches, we showed that SsATG8, one of the core components of the autophagy machinery, and its interactor SsNBR1, an autophagy cargo receptor, are important for vegetative growth, sclerotial formation, oxalic acid (OA) production, compound appressoria development, and virulence of S. sclerotiorum. Complementation assays with chimeric fusion constructs revealed that both LDS [AIM (ATG8 interacting motif) / LIR (LC3-interacting region) docking site] and UDS [UIM (ubiquitin-interacting motif) docking site] sites of the SsATG8 are required for its functions in autophagy and pathogenesis. Importantly, Δ Ssatg8 and Δ Ssnbr1 mutants showed enhanced sensitivity to the exogenous treatment with the proteasome inhibitors bortezomib and carfilzomib, and Δ Ssnbr1 mutant had decreased expression of SsATG8 under the proteasomal stress conditions, suggesting that a cross-talk exists between ubiquitin–proteasome and selective autophagy pathways, which enables downstream protein degradation to proceed properly during diverse biological processes. Collectively, our data indicate that SsATG8- and SsNBR1-mediated autophagy is crucial for S. sclerotiorum development, proteasomal stress response and virulence. [ABSTRACT FROM AUTHOR]