# The Compatibility of the Epichloë bromicola–Hordeum Association

## TL;DR

This study explores why a specific fungus struggles to form a beneficial relationship with cultivated barley, offering insights for improving crop resilience.

## Contribution

The study identifies specific gene expression changes and hyphal morphology issues in incompatible barley-fungus pairings.

## Key findings

- E. bromicola in Hv+Eb showed hyphal vacuolization compared to other associations.
- Fungal colonization altered trichome morphology and induced stomatal closure in hosts.
- sidN and Nox genes were significantly downregulated in Hv+Eb compared to Hb+Eb and NHb+Eb.

## Abstract

Background: Artificial inoculation of Epichloë endophytes into elite forage germplasm aims to establish beneficial symbioses for developing high-yield, high-quality, and stress-tolerant cultivars, but host specificity of the fungi often causes compatibility issues in non-natural hosts. Methods: The E. bromicola isolated from native wild barley was inoculated into cultivated wild barley (Hordeum brevisubulatum) and cultivated barley (Hordeum valgare), forming Hb+Eb and Hv+Eb. The NHb+Eb (native wild barley naturally infected with E. bromicola) served as a control. We analyzed fungal colonization patterns and symbiotic gene regulation to clarify the compatibility between E. bromicola and non-natural hosts. Results: Compared with NHb+Eb and Hb+Eb, E. bromicola in Hv+Eb showed obvious hyphal vacuolization. E. bromicola colonization altered host trichome morphology and induced stomatal closure. Correspondingly, expression of the siderophore biosynthesis gene sidN and the NADPH oxidase complex genes (NoxA, NoxB, NoxR, RacA) was significantly lower (p < 0.05) in Hv+Eb than in Hb+Eb and NHb+Eb. Conclusions: This study reveals that the incompatibility between cultivated barley and E. bromicola is characterized by altered hyphal morphology, which is linked to the downregulation of sidN and Nox. These findings provide a critical theoretical foundation for developing highly compatible cereal-Epichloë germplasms.