Caracterização funcional de uma lipase/esterase secretada por Xylella fastidiosa como fator de virulência chave na patogênese da Doença de Pierce

Abstract

Pierce s Disease (PD) of grapevines is caused by the bacterium Xylella fastidiosa (Xf), a xylem-limited gamma-proteobacterium that is responsible for several economically important diseases in many plants. A characteristic symptom of PD is leaf scorching, with regions of chlorosis progressing into necrotic zones at the peripheral margins of infected leaves. The occlusion of xylem elements and interference with water transport by Xf and its associated biofilm have been hypothesized as the main cause of PD symptom development; however, Xf virulence mechanism has not been elucidated. The analysis of Xf Temecula 1 secretome revealed a putative lipase/esterase (PD1703) that was abundantly secreted in the bacterial culture supernatant, and was characterized as a protein ortholog of the cell wall degrading enzyme LipA of Xanthomonas strains. The LipA was secreted and associated with a biofilm filamentous network and additional proteomic analysis revealed its abundant presence in outer membrane vesicles (OMVs). Accumulation of LipA in leaf regions was positively associated with PD symptoms and inversely correlated with bacterial titer. The lipase/esterase was found to elicit a hypersensitive response in grapevine and was regulated by quorum-sensing signaling, which is known to modulate bacterial pathogenesis. We propose that Xff pathogenesis is caused by LipA secretion mediated by OMV cargos, and its release and accumulation in leaf margins leads to the observed PD symptoms development.