A secretory protein from “ candidatus Liberibacter asiaticus” targets SNARE protein CsVTI13 to suppress autophagosome-vacuole fusion and promote bacterial infection

Macroautophagy/autophagy functions in plant host immunity responses to pathogen infection. The molecular mechanisms and functions used by the citrus Huanglongbing (HLB)-associated intracellular bacterium "Candidatus Liberibacter asiaticus" (CLas) to manipulate autophagy are largely unknown. Here, we identified a CLas effector, SDE4580 (CLIBASIA_04580), which contributes to HLB progression. Transgenic SDE4405 in Wanjincheng orange (Citrus sinensis) promotes CLas proliferation and symptom expression, while inhibiting autophagosome-vacuole fusion. Further investigations revealed that SDE4580 interacts with the citrus SNARE protein CsVTI13, which positively regulates autophagosome-vacuole fusion and limits pathogen proliferation. CsVTI13 interacts with CsSYP22, which acts as a bridge connecting CsVTI13 to CsATG8g, a process that is critical for the CsVTI13-mediated promotion of autophagic flux. Additional analyses demonstrated that SDE4580 competitively disrupts the interaction between CsVTI13 and CsSYP22, thereby inhibiting CsVTI13-mediated autophagy. Our findings demonstrate the role of SDE4580 in manipulating SNARE proteins for disrupting autophagosome-vacuole fusion and impairing autophagy-mediated antimicrobial defenses, unraveling a novel pathogen strategy to counteract defense-related autophagy during plant-bacteria interaction.Abbreviations: ATG: autophagy related; BSMV: barley stripe mosaic virus; BiFC: bimolecular fluorescence complementation; BTH: benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester; CLas: Candidatus Liberibacter asiaticus; co-IP: co-immunoprecipitation; CsACD2: ACCELERATED CELL DEATH 2; HLB: Huanglongbing; N. benthamiana: Nicotiana benthamiana; PhoA: alkaline phosphatase; PtdIns3K: phosphatidylinositol 3-kinase; SNARE: soluble N-ethylmaleimide-sensitive factor attachment protein receptor; VPS34: vacuolar protein sorting 34; WT: wild-type; Y2H: yeast two-hybrid.