# Cysteine-Mediated Root Growth Promotion in Strawberry (Fragaria × ananassa) Induced by TgSWO-Overexpressing Trichoderma

## TL;DR

A genetically modified fungus boosts strawberry root growth by promoting cysteine-related development and reducing plant defense responses.

## Contribution

Genetically engineered Trichoderma overexpressing TgSWO improves strawberry root growth via cysteine-mediated mechanisms.

## Key findings

- Strawberry seedlings treated with TgSWO-overexpressing Trichoderma showed increased root and shoot biomass.
- Transcriptome analysis revealed reduced defense gene activity and increased cell-wall and hormone signaling genes.
- Cysteine was identified as a key metabolite promoting growth, confirmed through exogenous application.

## Abstract

Strawberry (Fragaria × ananassa) is a globally important economic crop valued for its nutritional and commercial significance. However, its growth is frequently challenged by various biotic and abiotic stresses. To enhance strawberry root development and resilience, we engineered a Trichoderma guizhouense NJAU4742 strain to overexpress the TgSWO gene, which encodes a plant cell-wall-loosening protein known to facilitate fungal penetration and colonization. Strawberry seedlings treated with the TgSWO-overexpressing T. guizhouense NJAU4742 strain (S-OE) exhibited significant improvements in shoot and root fresh weights, root surface area, and number of root tips, showing 1.37- to 2.00-fold increases compared with the strawberry seedlings inoculated with the wild-type T. guizhouense NJAU4742 (S-WT) and 2.00- to 3.44-fold increases compared with the uninoculated strawberry seedlings (S-CK). Field-emission scanning electron microscopy (SEM) of the S-OE roots revealed denser hyphal colonization. Transcriptome analysis of S-OE showed a decrease in genes related to defense and detoxification, while genes for cell-wall growth and hormone signaling increased, shifting focus from defense to growth. Metabolomic profiling identified cysteine as a key metabolite associated with induced growth, which was further validated through exogenous cysteine application experiments. This study highlights the potential of genetically enhanced Trichoderma for improving strawberry growth and provides new insights into root–microbe interactions and metabolite-mediated plant development.