Genetic, molecular and expression features of the Pervenets mutant leading to high oleic acid content of seed oil in sunflower | [Caractéristiques génétiques, moléculaires et expression des gènes du mutant du tournesol Pervenets donnant une teneur élevée d'acide oléique dans l'huile de graine de tournesol]

Pervenets is a sunflower population that displays seed oil with a high oleic acid content (HOAC). The aim is to reconcile all the data gathered on this mutant in a unique explanatory mechanism. All Pervenets-derived (HOAC) lines display no accumulation or a very reduced accumulation of the delta12-desaturase transcript in the embryos during the stages for oil accumulation. They also carry oleHOS specific RFLP markers revealed by an delta12-desaturase cDNA used as a probe. The linoleic or LO genotypes do not carry this RFLP marker, but another allele: oleLOR (oleHL locus). Linkage disequilibrium between the oleHOS allele and HOAC was verified. The mode of inheritance of HOAC in two segregating populations was studied. A F2 progenies revealed one dominant allele for HOAC that co-segregated with the oleHOS allele showing that the Pervenets mutation and oleHOS were closely linked. F6 recombinant inbred lines, showed the HOAC trait due to two independent loci: the locus carrying the oleHOS allele and another locus sup. One allele, supole, at this second locus may suppress the effect of the oleHOS allele on the HOAC trait. Northern analyses performed on HOAC lines and F1 (OAC x LO) hybrids revealed under-accumulation of delta12-desaturase transcript. Thus Pervenets mutation acts in trans. The oleHOS genomic region that may carry the Pervenets mutation was cloned. A genomic library was constructed in lambdafixll with the DNA from the RHA345 HOAC line and screened with a delta12-desaturase cDNA as a probe. Two overlapping clones were entirely sequenced and revealed carrying a gene for an delta12-desaturase probably located in the RE. This corresponds to the invariant part of the oleHL locus. Another clone (11.1) probably carries delta12-desaturase repeated sequences that cause instability of the clone. It was showed that the 11.1 clone carries most of cDNA sequence, but due to its organization it is not yet sequenced. A mutation mechanism is proposed: duplicated delta12-desaturase sequences probably act in trans to silence the normal gene. The existence of gene silencing for the Pervenets mutation and modifier alleles (supole) that probably act on gene silencing mechanism have never been suggested to explain HOAC trait. These facts and explanations may explain the discordant results found in literature