Genetic, molecular and expression features of the Pervenets mutant leading to high oleic acid content of seed oil in sunflower

Abstract

Pervenets is a sunflower population that displays seed oil with a high oleic acid content [HOAC]. Our 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 Δ12-desaturase transcript in the embryos during the stages for oil accumulation. They also carry oleHOS specific RFLP markers revealed by an Δ12-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. We studied the mode of inheritance of [HOAC] in two segregating populations. 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 ([HOAC] x [LO]) hybrids revealed under-accumulation of Δ12-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 λfixll with the DNA from the RHA345 [HOAC] line and screened with a Δ12-desaturase cDNA as a probe. Two overlapping clones were entirely sequenced and revealed carrying a gene for an Δ12-desaturase probably located in the RE. This corresponds to the invariant part of the oleHL locus. Another clone (11.1) probably carries Δ12-desaturase repeated sequences that cause instability of the clone. We showed that the 11.1 done carries most of cDNA sequence, but due to its organization it is not yet sequenced. A mutation mechanism is proposed: duplicated Δ12-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.