A peroxisomal sterol carrier protein 2 (Scp2) contributes to lipid trafficking in differentiation and virulence of the insect pathogenic fungus Beauveria bassiana.

Sterol carrier protein 2 (SCP2) represents a family of proteins binding a variety of lipids and plays essential roles in cellular physiology. However, its physiological roles are largely unknown in filamentous fungi. In this study, we functionally characterized an orthologous Scp2 gene in the filamentous insect pathogenic fungus Beauveria bassiana (BbScp2). BbScp2 was verified to be a peroxisomal protein and displayed different affinities to various lipids, with strong affinity to palmitic acid (PA) and ergosterol (ES). No significant binding activity was detected between protein and oleic acid (OA) or linoleic acid (LA). Ablation of BbScp2 did not cause significant effects on fungal growth on various carbon sources, but resulted in a modest reduction in conidial (49%) and blastospore yield (45%). In addition, exogenous lipids could recover the defectives in conidiation of ΔBbScp2 mutant strain. BbScp2 was required for the cytomembrane functionality in germlings, and its loss resulted in a more significant decrease in virulence indicated by cuticle infection assay than intrahemocoel injection assay. Our findings indicate that Scp2 links the lipid trafficking to the asexual differentiation and virulence of B. bassiana.

Different contributions of the peroxisomal import protein Pex5 and Pex7 to development, stress response and virulence of insect fungal pathogen Beauveria bassiana.

AIMS: Peroxins Pex5 and Pex7 belong to the peroxisomal import machinery and recognize proteins containing peroxisomal targeting signal (PTS) type 1 and type 2, respectively. This study seeks to characterize these two peroxins in the entomopathogenic fungus Beauveria bassiana. METHODS AND RESULTS: The orthologs of Pex5 and Pex7 in B. bassiana (BbPex5 and BbPex7) were functionally analyzed via protein localization and gene disruption. BbPex5 and BbPex7 were associated with peroxisome and specifically required for PTS1 and PTS2 pathways, respectively, which were demonstrated to be involved in development, tolerance to oxidative stress and virulence. ΔBbPex5 mutant displayed additionally defectives that were undetected in ΔBbPex7 in vegetative growth and resistance to osmotic and cell wall-perturbing stresses. Notably, Woronin body major protein Hex1 with PTS1 linked this organelle to the development and virulence of B. bassiana, which indicates that Woronin body is associated with the roles of PTS1 pathway. CONCLUSION: Both PTS1 and PTS2 pathways are involved in broad physiological process, and the PTS1 pathway acts as a main peroxisomal import pathway. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the functional divergence of different peroxins and improves our understanding of organellar physiology involved in biocontrol potential of the entomopathogenic fungi.