First published online April 9, 2002; 10.1104/pp.010956
Plant Physiol, May 2002, Vol. 129, pp. 310-320
Fatty Acid and Lipid Biosynthetic Genes Are Expressed at Constant
Molar Ratios But Different Absolute Levels during
Embryogenesis1
Paul
O'Hara,
Antoni R.
Slabas, and
Tony
Fawcett*
Department of Biological Sciences, University of Durham, South
Road, Durham DH1 3LE, United Kingdom
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.
1
This work was supported by the Biotechnology and
Biological Science Research Council under the Resource Allocation and
Stress in Plants initiative (grant no. RSP 07674).
*
Corresponding author; e-mail tony.fawcett{at}durham.ac.uk; fax
191-374-2417.
© 2002 American Society of Plant Physiologists
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