Gene Cloning and Characterization - Genetics, Genomics and Breeding of Crop Plants - page 186

(ZVG437) representing a specific RFLP marker (Berry et al. 1995) was
sequenced and through BLASTN and BLASTX analyses was found to be
homologous to the 3' end of AHAS genes isolated from common cocklebur
( Xanthium stromarium L., U16279 and U16280; Bernasconi et al. 1995). Three
forward primers (p-AHAS-1, p-AHAS-2, and p-AHAS-3) were designed
from the 5'end of the cocklebur AHAS cDNA and two reverse primers (p-
AHAS-4 and p-AHAS-5) were derived from the ZVG437 cDNA probe. In a
second strategy, the nucleotide sequences of the cocklebur and lettuce ( Lactuca
sp.) AHAS genes (Mallory-Smith et al. 1990) were aligned. Moderately
degenerate forward and reverse primers were then designed based on
conserved sequences (Kolkman et al. 2004). These primers were used to
amplify the AHAS genes from genomic sunflower DNA. The 5' and 3' ends
of the coding sequences were completed by genome walking using the
Universal Genomewalker kit. Three AHAS genes ( AHAS1, AHAS2 , and
AHAS3 ) were cloned and sequenced from herbicide-resistant (mutant) and
susceptible (wild type) genotypes (Kolkman et al. 2004). Two of the three
sunflower AHAS genes were highly homologous. The nucleotide sequences
of AHAS1 and AHAS2 were 92% identical, whereas AHAS3 was 72% identical
to AHAS1 and 73% identical to AHAS2 . Fourty-eight SNPs were identified in
AHAS1 , a single six-base pair insertion-deletion in AHAS2 , and a single
SNP in AHAS3 . No DNA polymorphism was found in AHAS2 among the
elite inbred lines. Only six of the 48 SNPs discovered in AHAS1 would
cause amino acid substitutions. With regard to the herbicide resistance, the
C-T mutation in codon 205 (Ala to Val) in AHAS1 confers resistance to IMI
and another C-T mutation in codon 197 (Pro to Leu) to SU herbicides. Both
mutations have been described for other plant genera as well (Tranel and
Wright 2002). White et al. (2003) reported an independent Ala205Val
mutation in an AHAS gene from common sunflower herbicide resistant
biotypes from South Dakota.
In Europe, where wild biotypes of sunflower do not occur, resistance to
imidazoline is now used for post-emergence weed control in new sunflower
hybrids under the label CLEARFIELD ® technology (Pfenning et al. 2008).
6.3.2 Genes Involved in Developmental Aspects in Sunflower
6.3.2.1 Embryogenesis and Plant Development
Higher plant embryogenesis is divided into two major phases: embryo
development (or morphogenesis) and seed maturation (West and Harada
1993). In Arabidopsis thaliana , the LEC1 ( LEAFY COTYLEDON1 ) gene
( AtLEC1 ) and the LIL1 ( LEAFY COTYLEDON1-LIKE) gene ( AtLIL ) have
distinct functions in embryogenesis (Kwong et al. 2003). Primers recognizing
conserved features of the LEAFY COTYLEDON1-LIKE (L1L) genes from A.