Alterations in specialized metabolism and antioxidant capacity of Nepeta sibirica L. as induced by two Trichoderma sp.

Abstract

Trichoderma spp. have been extensively explored and used in agriculture due to their well-known biological control mechanisms. Fungi of the genus Trichoderma produce secondary metabolites which affect plant metabolism by stimulating the production of defense-related compounds and increasing the antioxidant capacity through enhanced polyphenol content and elevated activity of antioxidant enzymes, a result of the excess production of reactive oxygen species. In this work, Nepeta sibirica plants were grown in vitro on solid medium treated with two Trichoderma strains (T. viride and T. harzianum). After three and six days of treatment, leaves were metabolically profiled for major phenolic acids (chlorogenic, caffeic, and rosmarinic acid), and iridoids content (cis,trans-nepetalactone and 1,5,9-epideoxyloganic acid), in parallel with the expression analysis of nepetalactone biosynthetic genes and regulatory genetic elements-transcription factors (TFs). Both fungal strains induced changes in phenolic acids production, while only T. harzianum induced elevated levels of iridoids. Biosynthetic genes GPPS, and IS, as well as TF MYC2, were the only genes with expression levels not affected by the treatments with micro fungi. The response of antioxidant enzymes in N. sibirica leaves was also studied. The most active antioxidant enzyme following the infection with T. viride and T. harzianum was peroxidase (POX). Catalase (CAT) and superoxide dismutase (SOD) activity were also affected by the treatments. Results indicate a possibility of using Trichoderma infection in N. sibirica to elicit the production of biologically active defense compounds.