Oil Composition Variations - Genetics, Genomics and Breeding of Crop Plants - page 273

the HOAC in the RIL carrying Pervenets. The Pervenets mutation is not
sufficient for a high oleic acid content.

3) RFLP 5.85 Eco RI and RFLP 8.0 Hind III: 82 RILs displayed both the 5.85

kb Eco RI and the 8.0 Hind III fragments. However, 14 RILs displayed
unusual RFLPs, 10 RILs displayed an extra 5.0 kb Eco RI instead of 8 kb,
and 4 RILs gave a 13 kb Hind III fragment instead of a 16 kb fragment.

4) PCR Pervenets specific fragment: 78 RILs displayed a 902 bp fragment

as expected. All lines displayed the 173 bp MOD fragment.

Skoric et al. (1996) reported unstable expression of the Ol gene for HOAC
in one progeny, but they recovered the HOAC trait in subsequent progenies.
Considered all together, the data suggested another independent locus that
enables the Pervenets mutation for HOAC.
8.2.3.2.5 A Model as the Pervenets Mutation Functions

The three main features of the Pervenets mutation are: 1) its expression is
mainly dominant over the traditional allele; 2) it corresponds to the
duplication of part of intron and exon 2 of the MOD gene; and 3) the absence
of the MOD transcript suggests a silencing mechanism as post-
transcriptional gene silencing.
Up to now, all mutations that modify fatty acid levels have been found
to be recessive against the wild type gene. In a few cases, it may behave as
codominant. No cases of regulation by silencing have been found for fatty
acid metabolism in plants. However, in cotton using transgene methods,
Liu et al. (2002) caused a total knockout of oleate desaturase leading to
HOAC oil in this species. This points out that a silencing model is conceivable
and functioning in plants. Moreover, a dominant suppressor of silencing
has been found in rice (Kusaka et al. 1993).
Sunflower breeders have frequently experienced the unexpected
behavior of the Pervenets mutation. According to breeders, the Pervenets
mutation seems to disappear or to be unstable. In the RIL family, a genetic
factor independent of the MOD locus with the Pervenets mutation directs
the oleic acid level. Because it behaves as a suppressor of the Pervenets
mutation (Lacombe and Bervillé 2001), we have called it “olesup” . We have
shown that in RILs carrying both the Pervenets mutation and “olesup”— in
RILs we cannot say whether it is dominant or recessive—the MOD transcript
level is restored. This fact means that “olesup” could act directly on the
silencing mechanism (Lacombe et al. 2009).
A suppressor explains perfectly that the Pervenets mutation may
“disappear” (the plant's oil composition is indistinguishable from
traditional sunflower) or be unstable when it segregates. We also have
observed some rearrangements in the Pervenets mutation. In this case, each
RIL family loses the Pervenets mutation and reverts to a traditional