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

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.

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

“…Despite the chemical diversity of PPO inhibitors, they are largely assumed to inhibited PPO in a similar fashion . Recent research has demonstrated variability in cross‐resistance depending on the target‐site mutation that occurs in PPO2 , specifically ΔG210 induces resistance to pyrimidinedione and diphenyl ether families, but lowers resistance in thiadiazole and oxadiazole families . Similarly, the recently reported G399A PPO2 mutation induced high level resistance in diphenyl ether and lower level resistance in pyrimidinedione and triazolinone .…”

“…Recent research has demonstrated variability in cross‐resistance depending on the target‐site mutation that occurs in PPO2 , specifically ΔG210 induces resistance to pyrimidinedione and diphenyl ether families, but lowers resistance in thiadiazole and oxadiazole families . Similarly, the recently reported G399A PPO2 mutation induced high level resistance in diphenyl ether and lower level resistance in pyrimidinedione and triazolinone . Recent research on the new PPO‐inhibiting herbicide trifludimoxazin indicated variability in PPO2 inhibition depending on the target‐site change at ΔG210 or R128…”

“…Another mutation at same site, the replacement of arginine with a hydrophobic leucine, induced a radical change in the enzyme conformation. However, this mutation R128L/G does not impact resistance to the oxadiazole family . One reason for this is that there is no hydrogen bond formed between R128 with oxadiazole, inducing no effect on oxadiazole and plants remains sensitive to this herbicide chemical family.…”

“…(Palmer amaranth) . The latest mutation conferring resistance to PPO inhibitors is a PPO2 substitution at position 399 (G399A) in a field‐selected A. palmeri population . So far, there have been no reported target‐site mutations occurring in chloroplast‐targeted PPO1 conferring resistance to PPO‐inhibitors in field‐evolved resistant weed species.…”

“…20 The latest mutation conferring resistance to PPO inhibitors is a PPO2 substitution at position 399 (G399A) in a field-selected A. palmeri population. 21 So far, there have been no reported target-site mutations occurring in chloroplast-targeted PPO1 conferring resistance to PPO-inhibitors in field-evolved resistant weed species. In all cases, these reported PPO2 target-site mutations did not provide complete prophylaxis against injury but did allow for greater survival for individuals carrying the mutation.…”