Stress response signaling and virulence: insights from entomopathogenic fungi

Abstract

The Ascomycete fungal insect pathogens, Beauveria and Metarhizium spp. have emerged as model systems with which to probe diverse aspects of fungal growth, stress response, and pathogenesis. Due to the availability of genomic resources and the development of robust methods for genetic manipulation, the last 5 years have witnessed a rapid increase in the molecular characterization of genes and their pathways involved in stress response and signal transduction in these fungi. These studies have been performed mainly via characterization of gene deletion/knockout mutants and have included the targeting of general proteins involved in stress response and/or virulence, e.g. catalases, superoxide dismutases, and osmolyte balance maintenance enzymes, membrane proteins and signaling pathways including GPI anchored proteins and G-protein coupled membrane receptors, MAPK pathways, e.g. (i) the pheromone/nutrient sensing, Fus3/Kss1, (ii) the cell wall integrity, Mpk1, and (iii) the high osmolarity, Hog1, the PKA/adenyl cyclase pathway, and various downstream transcription factors, e.g. Msn2, CreA and Pac1. Here, we will discuss current research that strongly suggests extensive underlying contributions of these biochemical and signaling pathways to both abiotic stress response and virulence.

Autophagy‐related gene BbATG11 is indispensable for pexophagy and mitophagy, and contributes to stress response, conidiation and virulence in the insect mycopathogen Beauveria bassiana

“…Oxidative stress is associated with the entire life cycle of B. bassiana , including the saprophytic and pathogenic stages (Huarte‐Bonnet et al ., ; Ortiz‐Urquiza and Keyhani, ), and oxidation tolerance determines the environmental fitness and biocontrol potential of insect mycopathogens (Chu et al ., ). Like the role of BbATG8 (Ying et al ., ), BbATG11 plays an important role in B. bassiana resistance to oxidative stress caused by menadione, which suggests that selective autophagy is required for fungal tolerance to oxidation.…”

The Thm1 Zn(II)2Cys6 transcription factor contributes to heat, membrane integrity and virulence in the insect pathogenic fungus Beauveria bassiana

“…The ability of invertebrate pathogens such as Metarhizium and Beauveria sp. to respond to a wide range of stress conditions has been shown to be important for both environmental survival and insect parasitism (Ortiz‐Urquiza and Keyhani, ). Successful infection requires mechanisms for mitigating osmotic, oxidative and temperature stress (Pedrini et al ., ; Ortiz‐Urquiza and Keyhani, ).…”

“…to respond to a wide range of stress conditions has been shown to be important for both environmental survival and insect parasitism (Ortiz‐Urquiza and Keyhani, ). Successful infection requires mechanisms for mitigating osmotic, oxidative and temperature stress (Pedrini et al ., ; Ortiz‐Urquiza and Keyhani, ). For example, in M. acridum , a specialized secreted catalase‐peroxidase acts as an oxidative stress scavenger on the cuticle surface (Li et al ., ).…”

Fungal stress biology: a preface to the Fungal Stress Responses special edition

“…Ortiz-Urquiza and Keyhani (2014) explain that the concept of stress has been rather poorly defined, and that related terminology may be used to refer to any/all condition(s) that differ from the optimum. This might imply that every change in condition can be interpreted as "stressful", and as numerous parameters are in a constant state of flux, organisms are continuously exposed to stress.…”