ROBERT D. SLOCUM
Research Interests: Plant
physiology, adaptation of plants to environmental stresses, nitrogen metabolism
in plants, plant molecular biology and biotechnology.
Research In Progress:
The synthesis of pyrimidine
nucleotides is a prerequisite for DNA synthesis and cell division in all
organisms. In plants,
pyrimidine-activated intermediates (UDP-sugars) are essential for the
biosynthesis of sucrose, consitutents of high-energy foods, and cellulose and
related polysaccharides, a source of fiber (clothing, paper, etc.) which
accounts for much of the earthÕs biomass.
Mechanisms by which the pyrimidine
pathway is regulated in plants are poorly understood. We cloned the first plant genes encoding the enzymes
aspartate transcarbamoylase (ATCase), and carbamoyl phosphate synthetase
(CPSase) which regulate the pyrimidine pathway in other organisms through
classic ÒfeedbackÓ inhibition. We
are presently conducting laboratory experiments which will allow us to discern
the molecular mechanisms regulating expression of ATCase and CPSase genes and
enzyme proteins in plants. This
work has the potential to greatly expand our understanding of how plant
hormones (e.g., cytokinins) and other factors influence cell division and how
the pyrimidine pathway interfaces with other nitrogen metabolic pathways, such
as arginine biosynthesis.
Selected Publications (Student authors are underlined):
Williamson CL, Lake MR and
Slocum RD (1996) Isolation and characterization
of
a cDNA encoding a pea ornithine transcarbamoylase and comparison with
other
transcarbamoylases. Plant Mol.
Biol. 31:
1087-1092.
Williamson CL, Lake MR and
Slocum RD (1996) A cDNA encoding carbamoyl
phosphate
synthetase large subunit (carB) from Arabidopsis (Accession No.
U40341)
(PGR 96-055). Plant Physiol. 111: 1354.
Brandenburg SA, Williamson
CL and Slocum RD (1998) Characterization of a
cDNA
encoding the small subunit of Arabidopsis carbamoyl phosphate synthetase
(Accession
No. U73175) (PGR 98-087). Plant Physiol. 117: 717.
Lake MR, Williamson CL and
Slocum RD (1998) Molecular cloning and
characterization
of a UDP-glucose-4-epimerase gene (galE) and its expression in
pea
tissues. Plant Physiol. Biochem. 36: 555-562.
Slocum, RD (1999) Regulation of pyrimidine biosynthesis in plants. Paths
Pyrimidines 7: 79-85.
Slocum RD, Nichols HF, III and
Williamson CL (2000) Purification and
characterization
of Arabidopsis ornithine transcarbamoylase (OTCase), a member
of
a distinct and evolutionarily-conserved group of plant OTCases. Plant Physiol.
Biochem. 38: 1-10.
Bassett ET, Bouchet BY,
Carr JM, Williamson CL, and
Slocum RD (2003) PALA-
mediated
pyrimidine starvation increases expression of aspartate
transcarbamoylase
(pyrB) in Arabidopsis seedlings. Plant Physiol. Biochem. 41:
695-703.
Schmidt A, Su Y-H,
Kunze R, Warner S, Hewitt M, Slocum
RD, Ludewig U, Frommer
WB,
Desimone M (2004) UPS1 and UPS2 from Arabidopsis mediate high affinity
transport
of uracil and 5-fluorouracil. J.
Biol. Chem. (submitted for publlication)
Hewitt MM, Carr JM,
Williamson CL, Slocum RD.
(2004) Effects of phosphate
limitation
on expression of genes encoding enzymes which regulate de novo
synthesis and salvaging of
pyrimidines in Arabidopsis. Plant
Physiol. Biochem.
(submitted
for publication).