Molecular and biochemical characterization of an induced mutation conferring imidazolinone resistance in sunflower |
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Authors: | Carlos A Sala Mariano Bulos Mariel Echarte Sherry R Whitt Robert Ascenzi |
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Institution: | (1) Biotechnology Department, NIDERA S.A., Ruta 8 km 376, Casilla de Correo 6, 2600 Venado Tuerto, Santa Fe, Argentina;(2) BASF Plant Science LLC, 26 Davis Drive, P.O. Box 13528, Research Triangle Park, Durham, NC 27709, USA |
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Abstract: | A partially dominant nuclear gene conferring resistance to the imidazolinone herbicides was previously identified in the cultivated
sunflower (Helianthus annuus L.) line CLHA-Plus developed by seed mutagenesis. The objective of this study was to characterize this resistant gene at
the phenotypic, biochemical and molecular levels. CLHA-Plus showed a complete susceptibility to sulfonylureas (metsulfuron,
tribenuron and chlorsulfuron) but, on the other hand, it showed a complete resistance to imidazolinones (imazamox, imazapyr
and imazapic) at two rates of herbicide application. This pattern was in close association with the AHAS-inhibition kinetics
of protein extracts of CLHA-Plus challenged with different doses of imazamox and chlorsulfuron. Nucleotide and deduced amino
acid sequence comparisons between resistant and susceptible lines indicated that the imidazolinone-resistant AHAS of CLHA-Plus
has a threonine codon (ACG) at position 122 (relative to the Arabidopsis thaliana
AHAS sequence), whereas the herbicide-susceptible enzyme from BTK47 has an alanine residue (GCG) at this position. Since the resistance
genes to AHAS-inhibiting herbicides so far characterized in sunflower code for the catalytic (large) subunit of AHAS, we propose
to redesignate the wild type allele as ahasl1 and the incomplete dominant resistant alleles as Ahasl1-1 (previously Imr1 or Ar
pur
), Ahasl1-2 (previously Ar
kan
) and Ahasl1-3 (for the allele present in CLHA-Plus). The higher tolerance level to imidazolinones and the lack of cross-resistance to other
AHAS-inhibiting herbicides of Ahasl1-3 indicate that this induced mutation can be used to develop commercial hybrids with superior levels of tolerance and, at the
same time, to assist weed management where control of weedy common sunflower is necessary. |
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Keywords: | |
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