Distinct patterns of control and expression amongst members of the PEP carboxylase kinase gene family in C4 plants.
We have examined the complexity of the phosphoenolpyruvate carboxylase kinase (PPCK) gene family in the C(4) monocots maize and sorghum. Maize contains at least four PPCK genes. The encoded proteins are similar to other phosphoenolpyruvate carboxylase (PEPC) kinases, in that they comprise a protein kinase domain with minimal extensions, except that two of the proteins contain unusual acidic insertions. The spatial and temporal expression patterns of the genes provide information about their presumed functions. Expression of ZmPPCK1 in leaves is mesophyll cell-specific and light-induced, indicating that it encodes the PEPC kinase that is responsible for the phosphorylation of leaf PEPC during C(4) photosynthesis. Surprisingly, ZmPPCK2 is expressed in leaf bundle sheath cells, preferentially in the dark. This suggests that a main function of the ZmPPCK2 gene product is to allow PEPC to function anaplerotically in bundle sheath cells in the dark without interfering with the C(4) cycle. ZmPPCK2, ZmPPCK3 and ZmPPCK4 are all induced by exposure of tissue to cycloheximide, whereas ZmPPCK1 is not. This suggests that the ZmPPCK2, ZmPPCK3 and ZmPPCK4 genes share the property that their expression is controlled by a rapidly turning over repressor. Sequence and expression data show that sorghum contains orthologues of ZmPPCK1 and ZmPPCK2.
Shenton
Matt
M
Plant Science Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
Fontaine
Véronique
V
Hartwell
James
J
Marsh
Justin T
JT
Jenkins
Gareth I
GI
Nimmo
Hugh G
HG
D000595:Amino Acid Sequence; D002244:Carbon / Q000378:metabolism*; D003001:Cloning, Molecular; D003513:Cycloheximide / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D008027:Light; D008969:Molecular Sequence Data; D005810:Multigene Family; D010788:Photosynthesis; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D045868:Sorghum / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D003313:Zea mays / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics
D010940:Plant Proteins; D002244:Carbon; D003513:Cycloheximide; C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases