title: Inheritance and molecular characterization of broad range tolerance to herbicides targeting acetohydroxyacid synthase in sunflower.
abstract: Ahasl1 is a multilallelic locus where all the induced and natural mutations for herbicide tolerance were described thus far in sunflower (Helianthus annuus L.). The allele Ahasl1-1 confers moderate tolerance to imidazolinone (IMI), Ahasl1-2, and Ahasl1-3 provides high levels of tolerance solely to sulfonylurea (SU) and IMI, respectively. An Argentinean wild sunflower population showing plants with high level of tolerance to either an IMI and a SU herbicide was discovered and used to develop an inbred line designated RW-B. The objectives of this work were to determine the relative level and pattern of cross-tolerance to different AHAS-inhibiting herbicides, the mode of inheritance, and the molecular basis of herbicide tolerance in this line. Slight or no symptoms observed after application of different herbicides indicated that RW-B possesses a completely new pattern of tolerance to AHAS-inhibiting herbicides in sunflower. Biomass response to increasing doses of metsulfuron or imazapyr demonstrated a higher level of tolerance in RW-B with respect to Ahasl1-1/Ahasl1-1 and Ahasl1-2/Ahasl1-2 lines. On the basis of genetic analyses and cosegregation test, it was concluded that tolerance to imazapyr in the original population is inherited as a single, partially dominant nuclear gene and that this gene is controlling the tolerance to four different AHAS-inhibiting herbicides. Pseudo-allelism test permitted us to conclude that the tolerant allele present in RW-B is an allelic variant of Ahasl1-1 and was designated as Ahasl1-4. Nucleotide and deduced amino acid sequence indicated that the Ahasl1-4 allele sequence of RW-B has a leucine codon (TTG) at position 574 (relative to the Arabidopsis thaliana AHAS sequence), whereas the enzyme from susceptible lines has a tryptophan residue (TGG) at this position. The utilization of this new allele in the framework of weed control and crop rotation is discussed.
authors.affiliation: Biotechnology Department, NIDERA S.A, Ruta 8 km 376, Casilla de Correo 6, 2600, Venado Tuerto, Santa Fe, Argentina. csala@nidera.com.ar
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Sala
authors.forename: Mariano
authors.initials: M
authors.lastname: Bulos
mesh_terms: D000095:Acetolactate Synthase / Q000378:metabolism*; D000483:Alleles; D001190:Arylsulfonates; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance / Q000235:genetics*; D056426:Genetic Loci / Q000235:genetics*; D006368:Helianthus / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D006540:Herbicides / Q000633:toxicity; D007093:Imidazoles; D040582:Inheritance Patterns / Q000235:genetics*; D008969:Molecular Sequence Data; D009525:Niacin / Q000031:analogs & derivatives; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013453:Sulfonylurea Compounds; D058728:Weed Control / Q000379:methods*
chemical_list: D001190:Arylsulfonates; D017931:DNA Primers; D006540:Herbicides; D007093:Imidazoles; D013453:Sulfonylurea Compounds; C050296:metsulfuron methyl; D009525:Niacin; C076656:imazapyr; D000095:Acetolactate Synthase