Genomic Organization of Fatty Acid Desaturase-2 (Fad2 ) and Fatty Acid Desaturase-6 (Fad6) ESTs in Maize
Mikkilineni, Venugopal
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https://hdl.handle.net/2142/87691
Description
Title
Genomic Organization of Fatty Acid Desaturase-2 (Fad2 ) and Fatty Acid Desaturase-6 (Fad6) ESTs in Maize
Author(s)
Mikkilineni, Venugopal
Issue Date
2000
Doctoral Committee Chair(s)
Rocheford, Torbert R.
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Language
eng
Abstract
Corn oil is primarily composed of palmitic, stearic, oleic, linoleic and linolenic fatty acids. Increased levels of oleic acid may enhance the nutritional and functional value of corn oil. The biochemical pathway for fatty acid biosynthesis indicates that a single enzyme, the delta12 desaturase, converts oleic (18: 1) to linoleic (18:2) by inserting a double bond at the delta-12 position. Fatty acid desaturase-2 (fad2) converts the oleic acid to linoleic acid in the endoplasmic reticulum while the plastidial fatty acid desaturase-6 (fad6) has been shown to be the gene responsible for the conversion of oleic acid to linoleic acids in the plastids in plants. Expressed Sequence Tag (EST) clones from putative maize homologs for fad2 and fad6 have been identified. The maize fad2 ESTs showed an amino acid homology of 67--77% to fad2 of Soybean, Arabidopsis and Brassica species. The maize fad6 ESTs share 81% percent amino acid identity with the Arabidopsis fad6. The maize fad6 ESTs maps to chromosome 1. fad2 ESTs map to chromosomes 4, 5 and 10. Our sequence results suggest that more than one fad2 gene may be expressed in embryos. Transcript analysis of the fad2 ESTs suggests that the gene is expressed in embryos at a peak at day 14 and then stays constant at 21, 28 and 35 days after pollination. A major oleic/linoleic acid QTL in bin 6.04 has been more finely mapped in two genetic backgrounds and confirmed through the development and analysis of near isogenic lines for the umc65 marker. None of the fad2 or fad6 clones mapped to bin 6.04 where a large QTL for oleic and linoleic acids has been identified. Furthermore, no QTL for oleic and linoleic acid were associated with the map locations of any of the fad2 or fad6 ESTs. This suggests, but does not prove, that QTL linked to umc65 or any of the other QTL, are not allelic variants of the structural gene fad2, but rather may be regulatory loci of some nature.
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