Fatty acid and lipid biosynthetic genes are expressed at constant molar ratios but different absolute levels during embryogenesis.
In plants, fatty acid and complex lipid synthesis requires the correct spatial and temporal activity of many gene products. Quantitative northern analysis showed that mRNA for the biotin carboxylase subunit of heteromeric acetyl-coenzyme A carboxylase, fatty acid synthase components (3-oxoacyl-acyl carrier protein [ACP] reductase, enoyl-ACP reductase, and acyl-ACP thioesterase), and stearoyl-ACP desaturase accumulate in a coordinate manner during Brassica napus embryogenesis. The mRNAs were present in a constant molar stoichiometric ratio. Transcript abundance of mRNAs for the catalytic proteins was found to be similar, whereas the number of ACP transcripts was approximately 7-fold higher. The peak of mRNA accumulation of all products was between 20 and 29 d after flowering; by 42 d after flowering, the steady-state levels of all transcripts fell to about 5% of their peak levels, which suggests that the mRNAs have similar stability and kinetics of synthesis. Biotin carboxylase was found to accumulate to a maximum of 59 fmol mg(-1) total RNA in embryos, which is in general agreement with the value of 170 fmol mg(-1) determined for Arabidopsis siliques (J.S. Ke, T.N. Wen, B.J. Nikolau, E.S. Wurtele [2000] Plant Physiol 122: 1057-1071). Embryos accumulated between 3- and 15-fold more transcripts per unit total RNA than young leaf tissue; the lower quantity of leaf 3-oxoacyl-ACP reductase mRNA was confirmed by reverse transcriptase-polymerase chain reaction. This is in conflict with analysis of B. napus transcripts using an Arabidopsis microarray (T. Girke, J. Todd, S. Ruuska, J. White, C. Benning, J. Ohlrogge [2000] Plant Physiol 124: 1570-1581) where similar leaf to seed levels of fatty acid synthase component mRNAs were reported.
O'Hara
Paul
P
Department of Biological Sciences, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
Slabas
Antoni R
AR
Fawcett
Tony
T
D064431:3-Oxoacyl-(Acyl-Carrier-Protein) Reductase; D000103:Acetyl-CoA Carboxylase / Q000235:genetics / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D015152:Blotting, Northern; D029688:Brassica napus / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases / Q000235:genetics / Q000378:metabolism; D015342:DNA Probes / Q000235:genetics; D050745:Enoyl-(Acyl-Carrier Protein) Reductase (NADPH, B-Specific); D064429:Fatty Acid Synthases / Q000235:genetics / Q000378:metabolism; D005227:Fatty Acids / Q000096:biosynthesis*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D008055:Lipids / Q000096:biosynthesis*; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D005810:Multigene Family; D009693:Nucleic Acid Hybridization; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012639:Seeds / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
D015342:DNA Probes; D005227:Fatty Acids; D008055:Lipids; D012333:RNA, Messenger; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D000429:Alcohol Oxidoreductases; D064431:3-Oxoacyl-(Acyl-Carrier-Protein) Reductase; C018747:acyl-(acyl-carrier-protein)desaturase; D050745:Enoyl-(Acyl-Carrier Protein) Reductase (NADPH, B-Specific); D064429:Fatty Acid Synthases; D019731:Carbon-Nitrogen Ligases; C019791:biotin carboxylase; D000103:Acetyl-CoA Carboxylase