Trichoderma afroharzianum behaves differently in interaction with pea plants under varying iron availability

Trichoderma afroharzianum T22 is widely recognized for enhancing plant stress resilience, yet its effects in pea plants may vary depending on iron (Fe) availability.

We assessed the impact of T22 on pea grown under differential Fe status through integrated physiological and omics analyses. We found that the benefits of T22 are highly context dependent, demonstrating improvements in photosynthesis and Fe/N accumulation under Fe deficiency but minimal effects under sufficiency. RNA-seq identified 262 DEGs under Fe deficiency and 555 DEGs under Fe sufficiency following T22 inoculation, with the latter primarily associated with basal metabolic functions, indicating potential colonization costs rather than adaptive responses. Particularly, T22 inoculation upregulated symbiosis-related genes (Nodule-specific GRPs, Major facilitator, sugar transporter-like), Fe transporters (NRAMPs, HMAs), and redox-associated genes (Glutathione S-transferase, Glutathione peroxidase) in the roots under Fe shortage, reflecting a coordinated response to enhance nutrient acquisition and stress tolerance. Microbiome profiling revealed that T22 reshaped the root community by enriching several bacterial taxa such as Comamonadaceae, Pseudomonadaceae, and Mitsuaria under Fe deficiency. These enriched bacterial taxa may act as potential "helpers" to T22 by providing complementary beneficial effects under Fe deficiency. In contrast, under Fe-sufficient conditions, microbial restructuring was largely limited to the enrichment of Rhizobiaceae and Pararhizobium. Fungal taxa showed minimal changes, except for the enrichment of Paecilomyces in response to T22 under Fe-deficient conditions.

These findings indicate that T22 acts in a context-dependent manner, with bacterial enrichment varying with Fe availability, while fungal taxa were largely unaffected.