The Molecular Mechanism of Fludioxonil Action Is Different to Osmotic Stress Sensing.

Katharina Bersching,Stefan Jacob

doi:10.3390/jof7050393

Abstract

The group III two-component hybrid histidine kinase MoHik1p in the filamentous fungus Magnaporthe oryzae is known to be a sensor for external osmotic stress and essential for the fungicidal activity of the phenylpyrrole fludioxonil. The mode of action of fludioxonil has not yet been completely clarified but rather assumed to hyperactivate the high osmolarity glycerol (HOG) signaling pathway. To date, not much is known about the detailed molecular mechanism of how osmotic stress is detected or fungicidal activity is initiated within the HOG pathway. The molecular mechanism of signaling was studied using a mutant strain in which the HisKA signaling domain was modified by an amino acid change of histidine H736 to alanine A736. We found that MoHik1pH736A is as resistant to fludioxonil but not as sensitive to osmotic stress as the null mutant ∆Mohik1. H736 is required for fludioxonil action but is not essential for sensing sorbitol stress. Consequently, this report provides evidence of the difference in the molecular mechanism of fludioxonil action and the perception of osmotic stress. This is an excellent basis to understand the successful phenylpyrrole-fungicides’ mode of action better and will give new ideas to decipher cellular signaling mechanisms.

Highlights

Crop losses in the agricultural sector due to diseases, pests and weeds are approximately assessed to be ranging up to 30% of crop production [1]
We generated the mutant strain MoHik1pH736A, in which the phosphorylation-based signal transfer in the HisKA domain of MoHik1p is impaired by replacing H736 with alanine A736 (Figure 1b) for biological validation and to uncover the riddle that osmoregulation is equal to fungicide action
It is known that fludioxonil action is specific to the group III histidine kinases (HK) of the high osmolarity glycerol (HOG) pathway and hyperactivates the osmotic

Summary

Introduction

Crop losses in the agricultural sector due to diseases, pests and weeds are approximately assessed to be ranging up to 30% of crop production [1]. That makes the active principle of this fungicide class one of the most interesting molecular mechanisms of action in plant-protection research. The phenylpyrrole fludioxonil (4-(2,2-difluoro-1,3-benzodioxol-4-yl)-1H-pyrrole-3-carbonitrile) is a nonsystemic fungicide and shows a remarkable broad activity across all fungal species (except Oomycetes), against the genera Botrytis, Fusarium, Magnaporthe, Aspergillus, Monilinia and Penicillium [2]. The high efficacy against different molds makes it suitable for both pre- and post-harvest treatments [3]. Despite this extraordinary activity and the successful usage as an agricultural fungicide worldwide, the mechanism of fludioxonil action in the HOG pathway has still not been clarified in detail

Objectives

Methods

Results

Conclusion