Single nucleotide mutation in the barley acetohydroxy acid synthase ( AHAS ) gene confers resistance to imidazolinone herbicides

Abstract

Induced mutagenesis can be an effective way to increase variability in self-pollinated crops for a wide variety of agronomically important traits. Crop resistance to a given herbicide can be of practical value to control weeds with efficient chemical use. In some crops (for example, wheat, maize, and canola), resistance to imidazolinone herbicides (IMIs) has been introduced through mutation breeding and is extensively used commercially. However, this production system imposes plant-back restrictions on rotational crops because of herbicide residuals in the soil. In the case of barley, a preferred rotational crop after wheat, a period of 9–18 mo is required. Thus, introduction of barley varieties showing resistance to IMIs will provide greater flexibility as a rotational crop. The objective of the research reported was to identify resistance in barley for IMIs through induced mutagenesis. To achieve this objective, a sodium azide-treated M 2 /M 3 population of barley cultivar Bob was screened for resistance against acetohydroxy acid synthase (AHAS)-inhibiting herbicides. The phenotypic screening allowed identification of a mutant line showing resistance against IMIs. Molecular analysis identified a single-point mutation leading to a serine 653 to asparagine amino acid substitution in the herbicide-binding site of the barley AHAS gene. The transcription pattern of the AHAS gene in the mutant (Ser653Asn) and WT has been analyzed, and greater than fourfold difference in transcript abundance was observed. Phenotypic characteristics of the mutant line are promising and provide the base for the release of IMI-resistant barley cultivar(s).

Analysis of acetohydroxyacid synthase1 gene in chickpea conferring resistance to imazamox herbicide

“…Herbicide treatment triggered significant changes in the transcript levels between the susceptible and the resistant inbred lines (Breccia et al 2013). Similarly, in the IMI resistant mutant line of the barley cultivar Bob with mutation S653N, a four-fold difference in the transcript levels between the mutant and the wild type in response to IMI herbicide treatment was reported (Lee et al 2011). In this study, since there is no significant difference in the AHAS1 transcript levels between the susceptible and the tolerant cultivars in Fig.…”

“…In barley, an increase in AHAS transcript was seen in mutant resistant to imazamox as compared to the wild type (Lee et al 2011). In sunflower and rice, tissue-specific reduction in transcript levels of AHAS gene in the wild type occurred in response to imazethapyr treatment (Qian et al 2009;Breccia et al 2013).…”

Assessment of Genetic Diversity among Barley Cultivars and Breeding Lines Adapted to the US Pacific Northwest, and Its Implications in Breeding Barley for Imidazolinone-Resistance

“…The regulatory subunit stimulates enzyme activity and is required for the feedback regulation of the branched-chain amino acid biosynthesis, whereas the catalytic subunit is solely responsible for the enzyme activity and is also the site of point mutation(s) that confers resistance against IMI-herbicides [16]. Due to the importance of the catalytic subunit in providing IMI-resistance, the genes encoding it have been studied in common wheat and assigned to group 6 chromosomes [6A ( imi3 ), 6B ( imi2 ) and 6D ( imi1 )], using nulli-tetrasomic lines [28].…”

Gene Targeting Without DSB Induction Is Inefficient in Barley

“…ALS is an endogenous gene encoding an enzyme for the biosynthesis of branched-chain amino acids which is the target of various agronomically important herbicides. A number of different mutations are known that confer herbicide resistance, including one in barley (Lee et al, 2011). ALS was widely used to analyze gene targeting in plants including tobacco ( Nicotiana tabacum ) (Lee et al, 1990; Townsend et al, 2009), Arabidopsis thaliana (Badur and Reiss, 2004; Prinzenberg, 2006) and rice.…”