Two eisosome proteins play opposite roles in autophagic control and sustain cell integrity, function and pathogenicity in Beauveria bassiana

Abstract

Pil1A and Pil1B are two core eisosome proteins that are homologous to yeast Pil1/Lsp1 or filamentous fungal Pil1A/Pil1B but have been unexplored in entomopathogenic fungi. Here we examined subcellular localization and functions of Pil1A and Pil1B in Beauveria bassiana, a fungal insect pathogen. Either localization or co-localization experiments of the two proteins demonstrated that Pil1A and Pil1B were simultaneously localized at the periphery of hyphal cells for formation of stable, punctuate spots in B. bassiana. This is different from a reliance of proper Lsp1/Pil1B localization upon Pil1/Pil1A in other fungi. Deletions of pil1A and pil1B caused opposite changes in expression of many autophagy-related genes and formation of intravacuolar autophagosomes. Such opposite changes were restored to nearly normal status by exogenous rapamycin, implicating a link of Pil1A/B to the target of rapamycin signalling pathway. All single/double deletion mutants of pil1A and pil1B lost almost all pathogenicity due to reduced ability to secrete Pr1 proteases for cuticle degradation. They also showed differential changes in cell wall integrity and multiple stress responses. These findings unveil opposite roles for Pil1A and Pil1B in autophagic regulation and an essentiality of both for cell integrity, function and pathogenicity of the fungal entomopathogen.

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 ., ).…”

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

“…Among the Pr1 genes, only CDEP1 and CDEP2 have been shown to be virulence factors although, as yet, most are functionally unknown in fungal insect pathogens. However, attenuated virulence was less likely to be associated with the development of fungal infection after entry into the insect hemocoel because both the fungal virulence through the cuticle‐bypassing infection and the dimorphic transition rate in the medium mimic of insect hemolymph were less affected by the absence of rtt109 as a gene essential for dimorphic transition in B. bassiana …”

“…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 .…”

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

“…5F). This observation suggested a block or delay in the germination of injected mutant conidia and the in vivo formation of hyphal bodies, which presumably accelerate intrahemocoel proliferation of fungal cells by yeast-like budding and host mummification to death (Zhu et al, 2016;Zhang et al, 2017). The possible block of dimorphic transition for in vivo formation of hyphal bodies were evidenced in the following in vitro experiments, in which conidia were incubated for 3 days in Czapek broth (CZB, i.e., agar-free CZA) or trehalosepeptone broth (TPB) mimic to insect hemolymph (Cai et al, 2018;Tong et al, 2018).…”

“…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.…”