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Plant Physiol, November 2001, Vol. 127, pp. 1287-1298
The Glyoxylate Cycle in an Arbuscular Mycorrhizal Fungus. Carbon
Flux and Gene Expression
Peter J.
Lammers,
Jeongwon
Jun,
Jehad
Abubaker,
Raul
Arreola,
Anjali
Gopalan,
Berta
Bago,1
Cinta
Hernandez-Sebastia,2
James W.
Allen,
David D.
Douds,
Philip
E.
Pfeffer, and
Yair
Shachar-Hill*
Department of Chemistry and Biochemistry, New Mexico State
University, Las Cruces, New Mexico 88001 (P.J.L., J.J., J.A., R.A.,
A.G., C.H.-S., J.W.A., Y.S.-H.); and United States Department of
Agriculture, Agricultural Research Service, Eastern Regional Research
Center, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038 (B.B.,
D.D.D., P.E.P.)
The arbuscular mycorrhizal (AM) symbiosis is responsible for
huge fluxes of photosynthetically fixed carbon from plants to the soil.
Lipid, which is the dominant form of stored carbon in the fungal
partner and which fuels spore germination, is made by the fungus within
the root and is exported to the extraradical mycelium. We tested the
hypothesis that the glyoxylate cycle is central to the flow of carbon
in the AM symbiosis. The results of 13C labeling of
germinating spores and extraradical mycelium with 13C2-acetate and
13C2-glycerol and analysis by nuclear magnetic
resonance spectroscopy indicate that there are very substantial fluxes
through the glyoxylate cycle in the fungal partner. Full-length
sequences obtained by polymerase chain reaction from a cDNA library
from germinating spores of the AM fungus Glomus
intraradices showed strong homology to gene sequences for
isocitrate lyase and malate synthase from plants and other fungal
species. Quantitative real-time polymerase chain reaction measurements
show that these genes are expressed at significant levels during the
symbiosis. Glyoxysome-like bodies were observed by electron microscopy
in fungal structures where the glyoxylate cycle is expected to be
active, which is consistent with the presence in both enzyme sequences
of motifs associated with glyoxysomal targeting. We also identified
among several hundred expressed sequence tags several enzymes of
primary metabolism whose expression during spore germination is
consistent with previous labeling studies and with fluxes into and out
of the glyoxylate cycle.
1
Present address: Departamento de
Microbiología del Suelo y Sistemas Simbióticos,
Estación Experimental del Zaidín, calle Profesor
Albareda, 1, 18008-Granada, Spain.
2
Present address: Department of Crop Science and Botany,
North Carolina State University, Raleigh, NC 27695-7631.
*
Corresponding author; e-mail yairhill{at}nmsu.edu; fax
505-646-2649.
© 2001 American Society of Plant Physiologists
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