Farnesol is utilized for isoprenoid biosynthesis in plant cells via farnesyl pyrophosphate formed by successive monophosphorylation reactions.
The ability of Nicotiana tabacum cell cultures to utilize farnesol (F-OH) for sterol and sesquiterpene biosynthesis was investigated. [(3)H]F-OH was readily incorporated into sterols by rapidly growing cell cultures. However, the incorporation rate into sterols was reduced by greater than 70% in elicitor-treated cell cultures whereas a substantial proportion of the radioactivity was redirected into capsidiol, an extracellular sesquiterpene phytoalexin. The incorporation of [(3)H]F-OH into sterols was inhibited by squalestatin 1, suggesting that [(3)H]F-OH was incorporated via farnesyl pyrophosphate (F-P-P). Consistent with this possibility, N. tabacum proteins were metabolically labeled with [(3)H]F-OH or [(3)H]geranylgeraniol ([(3)H]GG-OH). Kinase activities converting F-OH to farnesyl monophosphate (F-P) and, subsequently, F-P-P were demonstrated directly by in vitro enzymatic studies. [(3)H]F-P and [(3)H]F-P-P were synthesized when exogenous [(3)H]F-OH was incubated with microsomal fractions and CTP. The kinetics of formation suggested a precursor-product relationship between [(3)H]F-P and [(3)H]F-P-P. In agreement with this kinetic pattern of labeling, [(32)P]F-P and [(32)P]F-P-P were synthesized when microsomal fractions were incubated with F-OH and F-P, respectively, with [gamma-(32)P]CTP serving as the phosphoryl donor. Under similar conditions, the microsomal fractions catalyzed the enzymatic conversion of [(3)H]GG-OH to [(3)H]geranylgeranyl monophosphate and [(3)H]geranylgeranyl pyrophosphate ([(3)H]GG-P-P) in CTP-dependent reactions. A novel biosynthetic mechanism involving two successive monophosphorylation reactions was supported by the observation that [(3)H]CTP was formed when microsomes were incubated with [(3)H]CDP and either F-P-P or GG-P-P, but not F-P. These results document the presence of at least two CTP-mediated kinases that provide a mechanism for the utilization of F-OH and GG-OH for the biosynthesis of isoprenoid lipids and protein isoprenylation.
Thai
L
L
Department of Biochemistry, Medical Center, College of Medicine, University of Kentucky, Lexington, KY 40536, USA.
Rush
J S
JS
Maul
J E
JE
Devarenne
T
T
Rodgers
D L
DL
Chappell
J
J
Waechter
C J
CJ
D002384:Catalysis; D002478:Cells, Cultured; D005204:Farnesol / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology; D010766:Phosphorylation; D017856:Phosphotransferases (Phosphate Group Acceptor) / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D010947:Plants, Toxic; D011106:Polyisoprenyl Phosphates / Q000096:biosynthesis* / Q000378:metabolism*; D012717:Sesquiterpenes; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism*
D010940:Plant Proteins; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; D005204:Farnesol; C004808:farnesyl pyrophosphate; D017856:Phosphotransferases (Phosphate Group Acceptor); C112479:farnesyl phosphate kinase