Discovery of a new intravacuolar protein required for the autophagy, development and virulence of Beauveria bassiana

Abstract

High proportions of hypothetical proteins exist in genomic databases of fungi, including putative secretory proteins (PSPs) likely involved in fungal invasion and virulence. Here we characterize one of many PSPs revealed in the previous transcriptome of Beauveria bassiana (a fungal insect pathogen) infecting a global lepidopteran pest and name it vacuole-localized protein 4 (VLP4) because this small, domain-lacking protein (22.96 kDa) was specifically localized in the vacuoles of hyphal cells. Deletion of VLP4 resulted in repression of almost all genes acting in autophagy and central development pathways. Consequently, the deletion mutant formed no autophagosome in hyphal vacuoles and displayed severe defects in aerial conidiation. conidial hydrophobicity to the insect surface, and secretion of cuticle-degrading Pr1 proteases required for normal cuticle infection. Blastospore formation was inhibited in the submerged mutant culture mimic to insect haemolymph, and formation of hyphal bodies in vivo was delayed. The fungal virulence was attenuated in the absence of VLP4. These phenotypic defects were well restored by targeted gene complementation. Our findings unveil a vital role of VLP4 in B. bassiana and call attention to many more PSPs for new insights into the interactions of fungal insect pathogens with insects.

Rtt109‐dependent histone H3 K56 acetylation and gene activity are essential for the biological control potential of Beauveria bassiana

“…The Rtt109 orthologue (NCBI accession code: EJP61638) located in the B. bassiana genome consists of 542 amino acids (molecular size: 59.52 kDa; isoelectric point: 9.67) encoded by an intron‐free genomic sequence of 1629 bp (tag locus: BBA_09410). The located Rtt109 sequence is featured with a HAT_KAT11 domain (residues 11–342) like the counterparts of S. cerevisiae and C. albicans (Fig.…”

“…Beauveria bassiana is an entomopathogenic fungus that usually undergoes an asexual cycle and has been integrated into pest management programs worldwide . The pest control potential of this insect pathogen is an output of diverse cellular processes and events, including conidial attachment to and germination on insect integument, hyphal penetration through the insect cuticle by means of the activities of secreted cuticle‐degrading enzymes, and the proliferation of fungal cells in insect hemocoel by yeast‐like budding until host death from mummification . Fungal response to the oxidative stress generated from host immunity defense is relevant to the success of fungal infection through cuticular penetration and of subsequent intrahemocoel proliferation, and hence important for fungal virulence .…”

Gcn5‐dependent histone H3 acetylation and gene activity is required for the asexual development and virulence of Beauveria bassiana

“…This is well in accordance with the loss of virulence or pathogenicity in the Δ gcn5 mutants of A. flavus (Lan et al ., ), C. neoformans (O'Meara et al ., ) and U. maydis (González‐Prieto et al ., ). Our data also unveil a vital role for Gcn5 in not only the biosynthesis and secretion of extracellular enzymes and Pr1 proteases presumably involved in the cuticle penetration crucial for the normal infection but also the dimorphic transition, which is essential for the rapid proliferation of fungal cells in insect haemocoel and hence determinant to the speed of host mummification to death (Wang et al ., 2016; Zhu et al ., ; Chu et al ., ; Zhang et al ., ). As far as known to date, only a very few members in the large family of cuticle degrading enzymes are functionally characterized, such as CDEP1/2 whose expression may augment the virulence of B. bassiana and bacterial crystal toxin (Zhang et al ., ; Fang et al ., ; Xia et al ., ).…”

“…Previously, B. bassiana conidiation was abolished in the absence of brlA or abaA and greatly inhibited in the absence of wetA or vosA (Li et al, 2015). The virulence of B. bassiana is a pleiotropic phenotype depending not only on the success of normal cuticle infection under the action of secreted cuticle-degrading enzymes but also on the speeds of intrahaemocoel fungal proliferation and host mummification to death Zhu et al, 2016;Chu et al, 2017;Zhang et al, 2017b). The virulence-related cellular events are of great diversity and complexity, such as dimorphic transition that turns cuticlepenetrating hyphae into unicellular blastospores (also called hyphal bodies), which facilitate fungal proliferation by yeast-like budding in host haemolymph and hence accelerate host mummification, and vice versa for fungal outgrowth at or near the time of host death and subsequent conidiation on the surfaces of insect cadavers.…”

Rei1‐like protein regulates nutritional metabolism and transport required for the asexual cycle in vitro and in vivo of a fungal insect pathogen

“…As a main source of fungal insecticides, B. bassiana has been widely applied for arthropod pest control (de de Faria and Wraight, ). The biological control potential of fungal insect pathogens is dependent on an ability to infect host through the normal route of cuticular penetration (Ortiz‐Urquiza and Keyhani, ) and to rapidly proliferate by yeast‐like budding in the host hemocoel until host mummification to death (Wang et al, ; Zhu et al, ; Chu et al, ; Zhang et al, ), as well as conidiation capacity, stress tolerance and virulence‐related cellular events (Zhang and Feng, ; Tong et al, ). The increasing up‐regulation of BbRei1 during the first 48‐h infection against P. xylostella implicates that it may take part in sustaining the fungal capability of cuticular penetration required for successful host infection and of intrahemocoel proliferation essential for host mummification.…”