First published online January 2, 2003; 10.1104/pp.011494
Plant Physiol, January 2003, Vol. 131, pp. 167-176
The Arabidopsis AtIPT8/PGA22 Gene Encodes an
Isopentenyl Transferase That Is Involved in De Novo Cytokinin
Biosynthesis1
Jiaqiang
Sun,2
Qi-Wen
Niu,2
Petr
Tarkowski,
Binglian
Zheng,
Danuse
Tarkowska,
Göran
Sandberg,
Nam-Hai
Chua, and
Jianru
Zuo*
Institute of Genetics and Developmental Biology, Chinese Academy of
Sciences, 917 Datun Road, Beijing 100101, China (J.S., B.Z., J.Z.);
Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, New York 10021 (Q.-W.N., N.-H.C., J.Z.); and
Umeå Plant Science Center. Department of Forest Genetics and Plant
Physiology, Swedish University of Agricultural Sciences, 901 83 Umeå,
Sweden (P.T., D.T., G.S.)
Cytokinin plays a critical role in plant growth and
development by stimulating cell division and cell differentiation.
Despite many years' research efforts, our current understanding
of this hormone is still limited regarding both its biosynthesis and
signaling. To genetically dissect the cytokinin pathway, we have used a
functional screen to identify Arabidopsis gain-of-function mutations
that enable shoot formation in the absence of exogenous cytokinins. By
using a chemical-inducible activation tagging system, we have identified over 40 putative mutants, designated as pga
(plant growth activators), which presumably were
affected in key components of cytokinin biosynthesis and signaling
pathway. Here, we report a detailed characterization of
pga22, a representative mutant from this collection. A
gain-of-function mutation in the PGA22 locus resulted in
typical cytokinin responses. Molecular and genetic analyses indicated
that PGA22 encodes an isopentenyl transferase (IPT)
previously identified as AtIPT8. Plants of the pga22
mutant accumulated at remarkably higher levels of
isopentenyladenosine-5'-monophosphate and isopentenyladenosine when
analyzed by mass spectrometry, suggesting that AtIPT8/PGA22 is a
functional IPT that may direct the biosynthesis of cytokinins in planta
via an isopentenyladenosine-5'-monophosphate-dependent pathway.
1
This work was supported by the E.I. DuPont de
Nemours and Company (grant to Rockefeller University), the Swedish
Natural Sciences Research Council (grant to G.S.'s laboratory), the
National Natural Science Foundation of China (NSFC; grant no. NSFC
30270142 to J.Z.), and by the Ministry of Science and Technology of
China (grant no. 2001AA225021 to J.Z.). J.Z. is a Bairen Jihua (Young Starter) fellow of the Chinese Academy of Sciences and a recipient of
the NSFC Outstanding Young Investigator Award.
2
These authors contributed equally to the paper.
*
Corresponding author; e-mail jrzuo{at}genetics.ac.cn; fax
8610-6487-3428.
© 2003 American Society of Plant Biologists
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