The first commercial herbicide-resistant trait in sunflower (Helianthus annuus L.) is known as 'Imisun'. Imidazolinone resistance in Imisun cultivars has been reported to be genetically controlled by a major gene (known as Imr1 or Ahasl1-1) and modifier genes. Imr1 is an allelic variant of the Ahasl1 locus that codes for the acetohydroxyacid synthase, which is the target site of these herbicides. The mechanism of resistance endowed by modifier genes has not been characterized and it could be related to non-target-site resistance. The objective of this study was to evaluate the role of cytochrome P450 monooxygenases (P450s) in Imisun resistance. The response to imazapyr herbicide in combination with P450s inhibitor malathion was evaluated in 2 Imisun

Imidazolinone resistance found in a wild sunflower (Helianthus annuus L.) population was successfully transferred to a cultivated inbred line developing ‘Imisun’ sunflowers. Genetic regulation of this trait has been reported to involve two genes: Imr1, an allelic variant of ahasl1 locus that codes for acetohydroxyacid synthase catalytic subunit, and the modifier Imr2, whose identity remains unknown, but it could be related to non‐target‐site resistance such as xenobiotic metabolism. The aim of the present study was to characterize the gene expression of resistant and susceptible sunflower lines in response to imazethapyr herbicide by complementary DNA amplified fragment‐length polymorphism (cDNA‐AFLP). Three assays were performed to determine (i) optimal herbicide treatment concentration, (ii) duration of herbicide treatment, and (iii) in vitro acetohydroxyacid synthase activity to assess enzyme inhibition levels. An important number of genes related to metabolism of xenobiotics and stress was found: cytochrome P450 monooxygenases, UDP‐glucuronosyl/UDP‐glucosyltransferases, glycosyltransferases, and ATP‐binding cassette transporters, among others. These results suggest that non‐target‐site resistance mechanisms may contribute to herbicide resistance in Imisun sunflower and could be related to the modifier gene Imr2. Using cDNA‐AFLP, we were able to detect candidate detoxification‐related genes potentially involved in imidazolinone resistance in sunflower.

The nature of non‐target‐site herbicide resistance (NTSR) to imidazolinone (IMI) in HA425 sunflower (Helianthus annuus L.) has not yet been fully characterized but could be related to xenobiotic metabolism. The objective of this study was to evaluate the role of cytochrome P450 monooxygenases (P450s) and other detoxification‐related proteins in NTSR in sunflower. Two sunflower inbred lines were used: HA 425, which is IMI resistant (Imisun), and HA 89, which is IMI susceptible. The growth response to the IMI herbicide imazethapyr in combination with the P450 inhibitors 1‐aminobenzotriazole (ABT) or piperonyl butoxide (PBO) was evaluated in 15‐d‐old sunflower plantlets. Roots were collected, and label‐free quantitation (LFQ) proteomic analysis was carried out to characterize the NTSR mechanisms involved in the IMI resistance trait in sunflower. The increased phytotoxicity of imazethapyr observed in the resistant line when ABT or PBO were present agrees with the hypothesis that NTSR mechanisms may contribute to herbicide resistance in sunflower. The herbicide treatment also led to changes in the levels of biotic and abiotic stress‐related proteins, glutathione S‐transferases, and cytochrome P450s, among others. Plant growth and root protein expression response to IMI herbicides in sunflower would be a combination of stress‐related and detoxification mechanisms. Understanding the basis of NTSR becomes helpful to exploit this trait in sunflower crop and to develop xenobiotic‐resistant, soil‐remediating cultivars.