Molecular similarity between gibberellic acid and gliotoxin: unravelling the mechanism of action for plant growth promotion by Trichoderma Harzianum

Abstract

Besides control of the fungal plant pathogens, another interesting aspect observed when plants are treated with Trichoderma harzianum include effects such as complete and even stand of plants, improved seed germination, increases in plant height and overall enhanced plant growth. No research has yet been conducted to elucidate the mechanism by which these effects occur. Improved seed germination, in particular, suggest that Trichoderma harzianum produces a metabolite that may mimic the plant growth hormone gibberellic acid. The metabolite gliotoxin, produced by Trichoderma harzianum appear to be structurally most similar to gibberellic acid. In this study, common pharmacophore generation and molecular ligand docking simulations were used to evaluate the molecular similarity between gibberellic acid, specifically GA3, and gliotoxin. For the common pharmacophore evaluation, the structure of various gibberellic acids were used to construct a pharmacophore space to which gliotoxin was aligned, and during the molecular docking simulations the gibberellic acid receptor, GID1, served as ligand target for GA3 and gliotoxin. During the common pharmacophore evaluation, gliotoxin was successfully aligned to the common pharmacophore model constructed from various gibberellic acids. Furthermore, molecular docking simulations of gliotoxin and GA3 into the gibberellic acid receptor (GID1) yielded docking scores of -10.78 kcal/mol for the GA3 molecule from Corina and a docking score of -10.17 kcal/mol for gliotoxin. The docking scores suggest that gliotoxin may be able to competitively occupy the receptor space for gibberellic acid, and as such elicit the similar physiological responses observed in literature.