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:


Regulation of plant pyrimidine nucleotide biosynthesis


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 earth’s 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 “feedback” 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: 



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).