Abstracts now available online - Euro Fed Lipid

Characterisation of a novel microsomal Lysophosphatidic Acid
Acyltransferase isoform of Brassica napus
Sylvie Maisonneuve 1 , Hélène Chiron 2 , Michel Delseny 2 and Thomas Roscoe 2
1
Laboratory of Plant Molecular Genetics, Graduate School of Biological Sciences, Nara
Institute of Science and Technology, Takayamacho 8916-5, Ikoma City, Nara
Prefecture, 630-0101 Japan
2
Laboratoire Genome et Developpement des Plantes, CNRS UMR5096, Université de
Perpignan, 52 Avenue de Villeneuve 66860 Perpignan, France
In higher plants, isozymes of Lysophosphatidic acid acyltransferase (LPAAT) located in
plastid and cytoplasmic compartments play a central role in determining the acyl
composition of phosphatidic acid, a key intermediate in the biosynthesis of membrane
and storage lipids. We have identified a multigene family in Arabidopsis thaliana
encoding proteins that contain motifs present in glycerolipid acyltransferases and that
possess sequence homologies to LPAATs but not to other acyltransferases. With the
objective to determine whether each member of the family encodes an authentic
LPAAT, we have cloned cDNA sequences coding for each isozyme from Arabidopsis
thaliana and we have begun the characterisation of certain homologous sequences
from Brassica napus. The strong sequence divergence, the distinct
compartmentalisation and the varying patterns of expression argue for a specific role for
each LPAAT-like protein in the production of phosphatidic acid required for diverse
cellular functions.
Since we are particularly interested in the role played by acyltransferases in the
synthesis of storage lipids we have assessed the contribution of seed expressed LPAAT
isoforms to triacylglycerol biosynthesis, (Maisonneuve, 2003). We have isolated cDNAs
from a Brassica napus immature embryo library that were predicted to code for two
distinct membrane proteins sharing approximately 60% amino acid identity and
possessing the glycerolipid acyltransferase molecular signature. Complementation of an
acyltransferase-deficient mutant of E. coli together with activity assays suggested that
each of the cDNAs encoded a functional LPAAT with the properties of a eukaryotic
pathway enzyme. Studies using RT-PCR revealed differences in the expression of the
genes encoding the two isoforms. One of the cDNAs was detected in all rapeseed
tissues and at each stage of embryo development, whereas the expression of the
second cDNA was restricted to roots, flowers and immature embryos. LPAAT
promoter::reporter fusions in Arabidopsis revealed a strong expression of this second
isoform in pollen.
Taken together, these results suggest that the ubiquitously expressed LPAAT isoform
may perform an essential housekeeping role in glycerolipid biosynthesis in all tissues.
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