Trichoderma Synthesizes Cytokinins and Alters Cytokinin Dynamics of Inoculated Arabidopsis Seedlings

Trichoderma is an important genus of symbiotic fungi, commonly used around the world as biocontrol agents and as biofertilizer. Although their beneficial effects are well known and are successfully exploited in sustainable agriculture practices, the biochemical mechanisms of plant growth-promoting actions of Trichoderma and their anti-pathogen characteristics are not well understood. This study biochemically surveyed 22 strains of Trichoderma and shows that Trichoderma produces cytokinins (CKs), which has not been reported to date. The phytohormone profiles ranged from 5.34 to 379.99 pmol CKs released to 10 mL of the growth medium and comprised riboside and nucleotide derivatives of cis-zeatin (cZ) and isopentenyladenine (iP), suggesting that fungal CKs originate from a tRNA degradation pathway. We reveal a connection between the levels of free base cZ produced by Trichoderma and the inhibition rate against the pathogen Fusarium graminearum among the tested strains. Furthermore, we analyzed CK profiles of Arabidopsis plants cultured in vitro in the presence of Trichoderma strains. The inoculated plants showed increased levels of cZ-type (cZR, cZROG) and iP-type (iP, iPR) CKs-the forms which dominated CK profiles of all the fungal in vitro cultures tested in this study. The increase in the levels of cZ derivatives was accompanied by a significant reduction in plant trans-zeatin (tZ)-type CKs (tZR, tZNT, tZOG, tZ7G, tZ9G) in Arabidopsis when co-cultured with the fungus. Our work suggests that CKs produced by plant symbiotic Trichoderma strains can be used for plant growth stimulation, may impact the colonization strategy of symbiotic fungi, and include alterations to the host plant phytohormones for enhanced plant resistance against pathogens.

Automated summary

This study biochemically surveyed 22 strains of Trichoderma and reveals that Trichoderma produces cytokinins (CKs), which has not been reported to date. The research suggests that the cytokinins produced by plant symbiotic Trichoderma strains may impact plant growth and resistance against pathogens.