From plant genomics to breeding practice

New alleles are constantly accumulated during intentional cropselection. The molecular understanding of these alleles hasstimulated new genomic approaches to mapping quantitativetrait loci (QTL) and haplotype multiplicity of the genes concerned. A limited number of quantitative trait nucleotides responsible forQTL variation have been described, but an acceleration in theirrate of discovery is expected with the adoption of linkagedisequilibrium and candidate gene strategies for QTL finemapping and cloning. Additional layers of regulatory variationhave been studied that could also contribute to the molecularbasis of quantitative genetics of crop traits. Despite thisprogress, the role of marker-assisted selection in plant breedingwill ultimately depend on the genetic model underlyingquantitative variation.

Source: Current opinion in biotechnology (2003) vol. 14, p. 214-219

Detection of a pathway from linoleate to a novel cyclopentenone: cis-12-oxo-10-phytoenoic acid in sunflower roots

The lipoxygenase pathway in sunflower roots was studied in vitro. A preliminary incubation of linoleic acid with 15 000 g supernatant of homogenate of sunflower roots (1.5-6 days after germination) revealed the predominant activity of 13-lipoxygenase. The exogenously added linoleic acid 13-hydroperoxide is further utilized through two competing pathways. One of them is directed towards formation of the ketodiene (9Z,11E)-13-oxooctadeca-9,11-dienoic acid. The second pathway, which is controlled by allene oxide synthase, leads to the formation of an alpha-ketol and a novel cyclopentenone, rac-cis-12-oxo-10-phytoenoic acid (12-oxo-PEA) via a short-lived allene oxide. Unexpectedly, the cyclopentenone 12-oxo-PEA is the predominant allene oxide synthase product. Identification of cis-12-oxo-PEA was confirmed by its UV, mass, (1)H NMR and 2D-COSY spectral data. The highest yield of 12-oxo-PEA is observed in very young roots (1.5-2 days after germination). The results of methanol-trapping experiments demonstrate that both 12-oxo-PEA and alpha-ketol are formed through the unstable allene oxide intermediate, (9Z)-12,13-epoxyoctadeca-9,11-dienoic acid, which is the primary product of allene oxide synthase. Since 12-oxo-PEA is a jasmonate congener, its biosynthesis in plants might be of physiological importance.

Source: Chembiochem. (2007) vol. 18, p. 2275-2280

Oxygenation of arachidonoyl lysophospholipids by lipoxygenases from soybean, porcine leukocyte, or rabbit reticulocyte

Oxygenation of arachidonoyl lysophosphatidylcholine (lysoPC) or arachidonoyl lysophosphatidic acid (lysoPA) by lipoxygenase (LOX) was examined. The oxidized products were identified by HPLC/UV spectrophotometry/mass spectrometry analyses. Straight-phase and chiral-phase HPLC analyses indicated that soybean LOX-1 and rabbit reticulocyte LOX oxygenated arachidonoyl lysophospholipids mainly at C-15 with the S form as major enantiomer, whereas porcine leukocyte LOX oxygenated at C-12 with the S form. Next, the sequential exposure of arachidonoyl-lysoPC to soybean LOX-1 and porcine leukocyte LOX afforded two major isomers of dihydroxy derivatives with conjugated triene structure, suggesting that 15(S)-hydroperoxyeicosatetraenoyl derivatives were converted to 8,15(S)-dihydroxyeicosatetraenoyl derivatives. Separately, arachidonoyl-lysoPA, but not arachidonoyl-lysoPC, was found to be susceptible to double oxygenation by soybean LOX-1 to generate a dihydroperoxyeicosatetraenoyl derivative. Overall, arachidonoyl lysophospholipids were more efficient than arachidonic acid as LOX substrate. Moreover, the catalytic efficiency of arachidonoyl-lysoPC as substrate of three lipoxygenases was much greater than that of arachidonoyl-lysoPA or arachidonic acid. Taken together, it is proposed that arachidonoyl-lysoPC or arachidonoyl-lysoPA is efficiently oxygenated by plant or animal lipoxygenases, C12- or C15-specific, to generate oxidized products with conjugated diene or triene structure.

Source: J Agric Food Chem. (2008) vol. 56, p. 1224-1232