Cytokinin activity of cis-zeatin and phenotypic alterations induced by overexpression of putative cis-Zeatin-O-glucosyltransferase in rice.
cis-Zeatin (cZ) is generally regarded as a cytokinin with little or no activity, compared with the highly active trans-zeatin (tZ). Although recent studies suggested possible roles for cZ, its physiological significance remains unclear. In our studies with rice (Oryza sativa), cZ inhibited seminal root elongation and up-regulated cytokinin-inducible genes, and its activities were comparable to those of tZ. Tracer experiments showed that exogenously supplied cZ-riboside was mainly converted into cZ derivatives but scarcely into tZ derivatives, indicating that isomerizations of cZ derivatives into tZ derivatives are a minor pathway in rice cytokinin metabolism. We identified three putative cZ-O-glucosyltransferases (cZOGT1, cZOGT2, and cZOGT3) in rice. The cZOGTs preferentially catalyzed O-glucosylation of cZ and cZ-riboside rather than tZ and tZ-riboside in vitro. Transgenic rice lines ectopically overexpressing the cZOGT1 and cZOGT2 genes exhibited short-shoot phenotypes, delay of leaf senescence, and decrease in crown root number, while cZOGT3 overexpressor lines did not show shortened shoots. These results propose that cZ activity has a physiological impact on the growth and development of rice.
RIKEN Plant Science Center, Tsurumi, Yokohama 230-0045, Japan.
Toru
T
Kudo
Nobue
N
Makita
Mikiko
M
Kojima
Hiroki
H
Tokunaga
Hitoshi
H
Sakakibara
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D003583:Cytokinins / Q000378:metabolism*; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D007536:Isomerism; D008969:Molecular Sequence Data; D012275:Oryza / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D016415:Sequence Alignment; D015026:Zeatin / Q000378:metabolism / Q000494:pharmacology*
D003583:Cytokinins; D010940:Plant Proteins; D015026:Zeatin; D005964:Glucosyltransferases