Proving the Mode of Action of Phytotoxic Phytochemicals.

Stephen O Duke,Zhiqiang Pan,Joanna Bajsa-Hirschel

doi:10.3390/plants9121756

Abstract

Knowledge of the mode of action of an allelochemical can be valuable for several reasons, such as proving and elucidating the role of the compound in nature and evaluating its potential utility as a pesticide. However, discovery of the molecular target site of a natural phytotoxin can be challenging. Because of this, we know little about the molecular targets of relatively few allelochemicals. It is much simpler to describe the secondary effects of these compounds, and, as a result, there is much information about these effects, which usually tell us little about the mode of action. This review describes the many approaches to molecular target site discovery, with an attempt to point out the pitfalls of each approach. Clues from molecular structure, phenotypic effects, physiological effects, omics studies, genetic approaches, and use of artificial intelligence are discussed. All these approaches can be confounded if the phytotoxin has more than one molecular target at similar concentrations or is a prophytotoxin, requiring structural alteration to create an active compound. Unequivocal determination of the molecular target site requires proof of activity on the function of the target protein and proof that a resistant form of the target protein confers resistance to the target organism.

Highlights

In this review, we define the mode of action (MOA) of a phytotoxin as the process by which it affects a plant, including its primary target site
Dayan et al [4] found a photosystem II (PSII) inhibitor effect on variable fluorescence in Amaranthus retroflexus L. grown in the same pot as a sorghum cultivar that secretes the allelochemical sorgoleone into the soil, indicating that sorgoleone is an allelochemical that contributes to the adverse effect of the sorghum cultivar on A. retroflexus
This is the only example of this approach to prove the role of an allelochemical of which we are aware, but this method is limited by the little we know of the MOA of allelochemicals and perhaps by few scientists taking advantage of this approach to prove allelopathy

Summary

Introduction

We define the mode of action (MOA) of a phytotoxin as the process by which it affects a plant, including its primary target site. Dayan et al [4] found a PSII inhibitor effect on variable fluorescence in Amaranthus retroflexus L. grown in the same pot as a sorghum cultivar that secretes the allelochemical sorgoleone into the soil, indicating that sorgoleone is an allelochemical that contributes to the adverse effect of the sorghum cultivar on A. retroflexus. This is the only example of this approach to prove the role of an allelochemical of which we are aware, but this method is limited by the little we know of the MOA of allelochemicals and perhaps by few scientists taking advantage of this approach to prove allelopathy

Objectives

Methods

Findings

Conclusion