Exploring the roles of fungal-derived secondary metabolites in plant-fungal interactions

Fungi can produce secondary metabolites (SMs), which play important roles in their stress responses. These compounds could also regulate their diverse relationships with plants, often resulting in significant inhibition or promotion effects on plant growth. Despite a long history of research of plant-fungal interactions, many questions remain regarding fungal SM clusters, their expressions and influences to host plants. Here, we review findings on SMs, SM gene clusters and their regulatory mechanisms in plant-associated fungi, along with current techniques to identify them. We also observed the transcriptional modulation of specific genes within the SM clusters of root endophytic fungus Colletotrichum tofieldiae, and discovered that several genes are suppressed in culture condi-tions without the host plant, yet become activated upon interaction with the host plant, implying the existence of host-mediated regulatory mechanisms. Furthermore, this article also focuses on fungal-derived phytohormone-mimicking SMs and their roles during plant-fungus interactions. Altogether, the aim of this article is to shed light on the largely unexplored potential of fungal SMs as mediators of plant growth modulation.