First published online July 18, 2002; 10.1104/pp.003087
Plant Physiol, August 2002, Vol. 129, pp. 1616-1626
A Role for Diacylglycerol Acyltransferase during Leaf
Senescence1
Marianne T.
Kaup,
Carol D.
Froese, and
John E.
Thompson*
Department of Biology, University of Waterloo, Waterloo, Ontario,
Canada N2L 3G1
Lipid analysis of rosette leaves from Arabidopsis has revealed an
accumulation of triacylglycerol (TAG) with advancing leaf senescence
coincident with an increase in the abundance and size of plastoglobuli.
The terminal step in the biosynthesis of TAG in Arabidopsis is
catalyzed by diacylglycerol acyltransferase 1 (DGAT1; EC 2.3.1.20).
When gel blots of RNA isolated from rosette leaves at various stages of
development were probed with the Arabidopsis expressed sequence tag
clone, E6B2T7, which has been annotated as DGAT1, a steep increase in
DGAT1 transcript levels was evident in the senescing leaves coincident
with the accumulation of TAG. The increase in DGAT1 transcript
correlated temporally with enhanced levels of DGAT1 protein detected
immunologically. Two lines of evidence indicated that the TAG of
senescing leaves is synthesized in chloroplasts and sequesters fatty
acids released from the catabolism of thylakoid galactolipids. First,
TAG isolated from senescing leaves proved to be enriched in
hexadecatrienoic acid (16:3) and linolenic acid (18:3), which are
normally present in thylakoid galactolipids. Second, DGAT1 protein in
senescing leaves was found to be associated with chloroplast membranes. These findings collectively indicate that diacylglycerol
acyltransferase plays a role in senescence by sequestering fatty acids
de-esterified from galactolipids into TAG. This would appear to be an
intermediate step in the conversion of thylakoid fatty acids to
phloem-mobile sucrose during leaf senescence.
1
This work was supported by the Natural Sciences
and Engineering Research Council of Canada.
*
Corresponding author; e-mail jet{at}sciborg.uwaterloo.ca; fax
519-746-2543.
© 2002 American Society of Plant Physiologists
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