A novel mutation A212T in chloroplast Protoporphyrinogen oxidase (PPO1) confers resistance to PPO inhibitor Oxadiazon in Eleusine indica

Abstract

BACKGROUND Protoporphyrinogen oxidase (PPO) with two isoforms, chloroplast‐targeted (PPO1) and mitochondrial‐targeted (PPO2), catalyzes a step in the biosynthesis of chlorophyll and heme. PPO1 and PPO2 are herbicide target sites of PPO‐inhibiting herbicides. Target‐site mutations conferring resistance to PPO inhibitors have all thus far been in PPO2. Oxadiazon is a unique PPO inhibitor utilized for preemergence Eleusine indica control. In this research, we evaluated the response of two previously confirmed oxadiazon‐resistant and susceptible E. indica biotypes to other PPO inhibitors and identified the resistance mechanism in two oxadiazon‐resistant E. indica biotypes. RESULTS Two E. indica biotypes were resistant to oxadiazon, but not to other structurally unrelated PPO inhibitors, such as lactofen, flumioxazin and sulfentrazone. A novel mutation A212T was identified in the chloroplast‐targeted PPO1, conferring resistance to oxadiazon in a heterologous expression system. Computational structural modeling provided a mechanistic explanation for reduced herbicide binding to the variant protein: the presence of a methyl group of threonine 212 changes the PPO1 active site and produces repulsive electrostatic interactions that repel oxadiazon from the binding pocket. CONCLUSION The novel A212T mutation in PPO1 conferring resistance specifically to PPO inhibitor oxadiazon was characterized. This is the first evidence of the direct role of PPO1 in the PPO mode of action, and the first evidence of evolved resistance in PPO1. © 2019 Society of Chemical Industry

Arg-128-Leu target-site mutation in PPO2 evolves in wild poinsettia (Euphorbia heterophylla) with cross-resistance to PPO-inhibiting herbicides

“…It is possible that some herbicides may prefer one of the targets (chloroplasts or mitochondria). For example, the Ala-212-Thr mutation found in E. indica PPO1 confers resistance to oxadiazon but not to other PPO inhibitors, indicating that oxadiazon may target only PPO1 (Bi et al 2020). The presence of a dual-target sequence should be investigated in E. heterophylla.…”

“…More recently, a single point mutation in PPO1 leading to an Ala-212-Thr amino acid change was found to confer resistance to oxadiazon in goosegrass [Eleusine indica (L.) Gaertn.] for the first time (Bi et al 2020). In addition to target-site mutations, resistance to PPO inhibitors was partially reverted by malathion, a cytochrome P450 monooxygenase (P450) inhibitor, suggesting that metabolic resistance to PPO herbicides could also evolve in A. palmeri (Varanasi et al 2018) and A. tuberculatus (Obenland et al 2019).…”

Differences in efficacy, resistance mechanism and target protein interaction between two PPO inhibitors in Palmer amaranth (Amaranthus palmeri)

“…Most recently, a resistance-endowing mutation was reported in goosegrass [ Eleusine indica (L.) Gaertn.] (Bi et al 2019). Furthermore, overexpression of PPX2 enzyme, although not yet found in any weed species, was used to generate transgenic crops with PPO-inhibitor resistance and thus could be another potential resistance mechanism that could evolve in weeds (Choi et al 1998; Lee et al 2000; Watanabe et al 2002).…”

First Report of Glyphosate-Resistant Biotype of Eleusine Indica (L.) Gaertn. in Europe

“…Integrating glyphosate with other herbicides with different SoA is recommendable for chemical control of E. indica in this area. Unfortunately, resistant biotypes to several herbicides and SoAs, such as the protoporphyrinogen oxidase (PPO) -inhibitor oxadiazon [44], ACCase-inhibitors [26,27] or the photosystem II inhibitor metribuzin [45], have already been reported in several countries. Specific strategies, such as rotation and/or a mixture of herbicides with different SoA, should be adopted to avoid the potential evolution of resistance to other herbicides.…”