A Novel Single-Site Mutation in the Catalytic Domain of Protoporphyrinogen Oxidase IX (PPO) Confers Resistance to PPO-Inhibiting Herbicides.

Gulab Rangani,Matheus M Noguera,Ana Claudia Langaro,Reiofeli A Salas-Perez,Thomas Mietzner,Nilda Roma-Burgos,Raphael A Aponte,Michael Knapp,Aimone Porri,Ian R Craig

doi:10.3389/fpls.2019.00568

Abstract

Protoporphyrinogen oxidase (PPO)-inhibiting herbicides are used to control weeds in a variety of crops. These herbicides inhibit heme and photosynthesis in plants. PPO-inhibiting herbicides are used to control Amaranthus palmeri (Palmer amaranth) especially those with resistance to glyphosate and acetolactate synthase (ALS) inhibiting herbicides. While investigating the basis of high fomesafen-resistance in A. palmeri, we identified a new amino acid substitution of glycine to alanine in the catalytic domain of PPO2 at position 399 (G399A) (numbered according to the protein sequence of A. palmeri). G399 is highly conserved in the PPO protein family across eukaryotic species. Through combined molecular, computational, and biochemical approaches, we established that PPO2 with G399A mutation has reduced affinity for several PPO-inhibiting herbicides, possibly due to steric hindrance induced by the mutation. This is the first report of a PPO2 amino acid substitution at G399 position in a field-selected weed population of A. palmeri. The mutant A. palmeri PPO2 showed high-level in vitro resistance to different PPO inhibitors relative to the wild type. The G399A mutation is very likely to confer resistance to other weed species under selection imposed by the extensive agricultural use of PPO-inhibiting herbicides.

Highlights

Weeds have been the major cause of crop yield losses since the dawn of agriculture
We found that the majority of survivors did not carry the G210 deletion mutation ( G210) that confers resistance to PPO inhibitors (Patzoldt et al, 2006)
The G399A mutation identified in PPO2 gene in fomesafen-resistant plants may occur in PPO1 as this site is conserved across PPO isozymes in various species (Supplementary Figure S2); the resistance-conferring mutation has been selected only in PPO2 of A. palmeri

Summary

Introduction

Weeds have been the major cause of crop yield losses since the dawn of agriculture. Herbicides are the primary tools used to manage weedy species. Weeds continue to be a growing threat to food security because of resistance to herbicides (Heap, 2018). The use of herbicides (synthetic organic chemicals) has been the dominant weed management technique since the ‘60s (Délye et al, 2013). While herbicides have greatly improved agricultural production, their intensive, and continuous use has resulted in the evolution of resistance in many weedy plant species (Powles and Yu, 2010). There are >480 unique cases of herbicide resistance reported globally, distributed over 252 weedy species and encompassing resistance to almost all (27) herbicide mechanisms of action (Heap, 2018)

Methods

Results

Discussion

Conclusion