# Plant recognition by Trichoderma Harzianum elicits upregulation of a novel secondary metabolite cluster required for colonization

## TL;DR

This study shows how the fungus Trichoderma harzianum responds to plants by activating a new gene cluster important for colonization and biocontrol.

## Contribution

Discovery of a novel gene cluster (PCA) in Trichoderma harzianum involved in plant recognition and colonization.

## Key findings

- T. harzianum B97 responds chemotropically to plant extracts and alters secondary metabolite secretion.
- The PCA gene cluster is strongly induced during plant recognition and is essential for plant colonization.
- The PCA cluster is unique to the Harzianum clade and likely acquired via horizontal gene transfer from plants.

## Abstract

Trichoderma harzianum is a filamentous ascomycete frequently applied as biocontrol agent in agriculture. While mycoparasitism and antagonism of Trichoderma spp. against fungal pathogens are well known, early fungal responses to the presence of a plant await broader investigation. Analyzing early stages of plant-fungus communication we show that T. harzianum B97 chemotropically responds to a plant extract and that both plant and fungus alter secondary metabolite secretion upon recognition. We developed a strategy for omics-analysis simulating conditions of early plant recognition eliciting a chemotropic response in the fungus and found 102 genes to be differentially regulated, including nitrate and nitrite reductases. Additionally, the previously uncharacterized Plant Communication Associated (PCA) gene cluster was strongly induced upon recognition of the plant, comprises a palindromic DNA motif and was essential for plant colonization. The PCA-cluster is only present in the Harzianum clade of Trichoderma and closely related to a homologous cluster in Metarhizium spp. Horizontal gene transfer (HGT) was detected for PCA-cluster genes by plants, while the cluster in T. harzianum is likely under balancing or positive selection. Hence, the PCA-cluster mediates early fungus-plant chemical communication and may be responsible for the high potential of T. harzianum and closely related species for biocontrol applications.

The online version contains supplementary material available at 10.1038/s41598-025-33935-2.