title: Higher plant cytochrome b5 polypeptides modulate fatty acid desaturation.
abstract: BACKGROUND
  Synthesis of polyunsaturated fatty acids (PUFAs) in the endoplasmic reticulum of plants typically involves the fatty acid desaturases FAD2 and FAD3, which use cytochrome b(5) (Cb5) as an electron donor. Higher plants are reported to have multiple isoforms of Cb5, in contrast to a single Cb5 in mammals and yeast. Despite the wealth of information available on the roles of FAD2 and FAD3 in PUFA synthesis, information regarding the contributions of various Cb5 isoforms in desaturase-mediated reactions is limited.
  
  
  RESULTS
  The present functional characterization of Cb5 polypeptides revealed that all Arabidopsis Cb5 isoforms are not similarly efficient in ω-6 desaturation, as evidenced by significant variation in their product outcomes in yeast-based functional assays. On the other hand, characterization of Cb5 polypeptides of soybean (Glycine max) suggested that similar ω-6 desaturation efficiencies were shared by various isoforms. With regard to ω-3 desaturation, certain Cb5 genes of both Arabidopsis and soybean were shown to facilitate the accumulation of more desaturation products than others when co-expressed with their native FAD3. Additionally, similar trends of differential desaturation product accumulation were also observed with most Cb5 genes of both soybean and Arabidopsis even if co-expressed with non-native FAD3.
  
  
  CONCLUSIONS
  The present study reports the first description of the differential nature of the Cb5 genes of higher plants in fatty acid desaturation and further suggests that ω-3/ω-6 desaturation product outcome is determined by the nature of both the Cb5 isoform and the fatty acid desaturases.
authors.affiliation: Division of Plant Sciences and National Center for Soybean Biotechnology, University of Missouri, Columbia, Missouri, United States of America. kraj.pgr@gmail.com
authors.forename: Rajesh
authors.initials: R
authors.lastname: Kumar
authors.forename: Lam-Son Phan
authors.initials: LS
authors.lastname: Tran
authors.forename: Anjanasree K
authors.initials: AK
authors.lastname: Neelakandan
authors.forename: Henry T
authors.initials: HT
authors.lastname: Nguyen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D015786:Cytochromes b5 / Q000737:chemistry* / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D044943:Fatty Acid Desaturases / Q000235:genetics; D005227:Fatty Acids / Q000737:chemistry* / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D010802:Phylogeny; D010944:Plants; D020033:Protein Isoforms; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013025:Glycine max / Q000378:metabolism
chemical_list: D017931:DNA Primers; D005227:Fatty Acids; D010455:Peptides; D020033:Protein Isoforms; D015786:Cytochromes b5; D044943:Fatty Acid Desaturases