Toward an integrated understanding of pathogenic and mutualistic lifestyles exhibited by plant-associated fungi

Abstract

Plants in nature interact with microbes exhibiting diverse lifestyles. The resulting plant phenotype reflects the lifestyles of microbes, with the effects ranging from beneficial, such as growth promotion or resilience to abiotic/biotic stress, commensal (neutral) to even pathogenic, i.e., growth inhibition or disease symptoms. It has been reported that microbes can convert their lifestyles depending on host environments; however, the genetic background, especially for microbes, remains elusive. Colletotrichum fungi are found in many plants as not only pathogens causing anthracnose disease but also endophytes showing beneficial or commensal effects on plant hosts. Since Colletotrichum fungi adopt diverse lifestyles and persist in various host environments, we utilize the fluctuating Colletotrichum lifestyles to unveil the molecular mechanisms that discriminate beneficial and pathogenic lifestyles under changing host environments. In this review, we first summarize previous findings on beneficial or pathogenic lifestyles in plant-microbe interactions, especially for the lifestyles of Colletotrichum fungi and the molecular background of the interaction. Additionally, we introduce our research on the “hidden” virulence of Colletotrichum tofieldiae endophytic isolates to investigate the mechanisms behind lifestyle transitions using Arabidopsis thaliana as a model. Finally, we discuss the potential ecological role of Colletotrichum fungi within its niche.