Agriculture Reference
In-Depth Information
V. GENETIC AND MOLECULAR BASES OF HIGH OLEATE TRAIT
The discovery of high oleate trait germplasm (see Section II A.2) in the
1980s provided opportunities to improve the seed chemistry and nutri-
tional value of peanut. Early investigations into the inheritance of high
oleate trait involving F435-2, a breeding line with exceptionally high
oleic (80%) and low linoleic (2%) acids, revealed that two loci (
ol1
and
ol2
) control high oleate in F435-2. Crosses between normal and high
oleate Virginia cultivars generated an F
2
segregation ratio of 15 normal:1
high oleic acid seed, supporting a two-gene model. Furthermore, some
runner and Virginia-type peanut cultivars with normal oleate phenotype
differ from F435-2 in having only
ol2
allele, and the F
2
seeds from these
crosses segregated into 3:1 ratio of normal to high oleic acid levels
(Moore and Knauft 1989; Isleib et al. 1996). These runner and Virginia-
type cultivars apparently already possessed the
ol1
gene. Similar work in
Spanish cultivars involving F435-2 indicated that both
ol1
and
ol2
loci
segregated in crosses with a source of high oleate trait. Variation in the
allelic composition at either or both loci showed variable segregation
patterns, thereby indicating that other genetic modi
ers may be involved
in the expression of the O/L ratio (López et al. 2001). Oleoyl-PC desa-
turase is involved in conversion of oleate to linoleate (Schwartzbeck
et al. 2001) and loss of function of oleoyl-PC desaturase causes the high
O/L trait in peanut (Ray et al. 1993). Molecular basis of the high oleate
phenotype in peanut revealed that two nonallelic homoeologous genes,
ahFAD2A
(A genome) and
ahFAD2B
(B genome), encoding oleoyl-PC
desaturases are involved in the expression of the high oleate phenotype.
A mutation in
ahFAD2A
and a signi
cant reduction in the levels of
the
ahFAD2B
transcript together cause the high oleate phenotype, while
one expressed gene encoding a functional enzyme is suf
cient for the
normal oleate phenotype in peanut genotypes (Jung et al. 2000a,b).
Further studies con
A)
and two alleles in
ahFAD2B
(either a nonsense mutation caused
by a single nucleotide insertion (441_442insA) or a transposable
element insertion) control the high oleate trait in peanut (Chu et al.
2007, 2009).
rmed that a mutant allele in
ahFAD2A
(448G
>
VI. SEQUENCING THE PEANUT GENOME AND IMPLICATIONS
IN BREEDING
'
genetic code, thereby facilitating discovery of the genes and identifying
Deoxyribonucleic acid (DNA) sequencing allows elucidating a species
