Mutations in the genes responsible for the synthesis of furan fatty acids resolve the light-induced off-odor in soybean oil.

Soybean oil is the second most produced edible vegetable oil and is used for many edible and industrial materials. Unfortunately, it has the disadvantage of 'reversion flavor' under photooxidative conditions, which produces an off-odor and decreases the quality of edible oil. Reversion flavor and off-odor are caused by minor fatty acids in the triacylglycerol of soybean oil known as furan fatty acids, which produce 3-methyl-2,4-nonanedione (3-MND) upon photooxidation. As a solution to this problem, a reduction in furan fatty acids leads to a decrease in 3-MND, resulting in a reduction in the off-odor induced by light exposure. However, there are no reports on the genes related to the biosynthesis of furan fatty acids in soybean oil. In this study, four mutant lines showing low or no furan fatty acid levels in soybean seeds were isolated from a soybean mutant library. Positional cloning experiments and homology search analysis identified two genes responsible for furan fatty acid biosynthesis in soybean: Glyma.20G201400 and Glyma.04G054100. Ectopic expression of both genes produced furan fatty acids in transgenic soybean hairy roots. The structure of these genes is different from that of the furan fatty acid biosynthetic genes in photosynthetic bacteria. Homologs of these two group of genes are widely conserved in the plant kingdom. The purified oil from the furan fatty acid mutant lines had lower amounts of 3-MND and reduced off-odor after light exposure, compared with oil from the wild-type.

Crystal structure of the novel lesion-specific endonuclease PfuEndoQ from Pyrococcus furiosus.

Because base deaminations, which are promoted by high temperature, ionizing radiation, aerobic respiration and nitrosative stress, produce mutations during replication, deaminated bases must be repaired quickly to maintain genome integrity. Recently, we identified a novel lesion-specific endonuclease, PfuEndoQ, from Pyrococcus furiosus, and PfuEndoQ may be involved in the DNA repair pathway in Thermococcales of Archaea. PfuEndoQ recognizes a deaminated base and cleaves the phosphodiester bond 5' of the lesion site. To elucidate the structural basis of the substrate recognition and DNA cleavage mechanisms of PfuEndoQ, we determined the structure of PfuEndoQ using X-ray crystallography. The PfuEndoQ structure and the accompanying biochemical data suggest that PfuEndoQ recognizes a deaminated base using a highly conserved pocket adjacent to a Zn2+-binding site and hydrolyses a phosphodiester bond using two Zn2+ ions. The PfuEndoQ-DNA complex is stabilized by a Zn-binding domain and a C-terminal helical domain, and the complex may recruit downstream proteins in the DNA repair pathway.

EndoQ and EndoV work individually for damaged DNA base repair in Pyrococcus furiosus.

Base deamination is a typical form of DNA damage, and it must be repaired quickly to maintain the genome integrity of living organisms. Endonuclease Q (EndoQ), recently found in the hyperthermophilic archaea, is an enzyme that cleaves the phosphodiester bond 5' from the damaged nucleotide in the DNA strand, and may primarily function to start the repair process for the damaged bases. Endonuclease V (EndoV) also hydrolyzes the second phosphodiester bond 3' from the damaged nucleotide, although the hyperthermophilic archaeal EndoV is a strictly hypoxanthine-specific endonuclease. To understand the relationships of the EndoQ and EndoV functions in hyperthermophilic archaea, we analyzed their interactions in hypoxanthine repair. EndoQ and EndoV do not directly interact with each other in either the presence or absence of DNA. However, EndoQ and EndoV individually worked on deoxyinosine (dI)-containing DNA at each cleavage site. EndoQ has higher affinity to dI-containing DNA than EndoV, and cells produce higher amounts of EndoQ, as compared to EndoV. These data support the proposal that EndoQ primarily functions for, at least, dI-containing DNA.