Plant and Cell Physiology Advance Access originally published online on December 15, 2005
Plant and Cell Physiology 2006 47(2):234-243; doi:10.1093/pcp/pci240
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Cytokinin Receptors are Required for Normal Development of Auxin-transporting Vascular Tissues in the Hypocotyl but not in Adventitious Roots
1 Institute of Biological Sciences, University of Tsukuba, Tsukuba, 305-8572 Japan
2 Bioscience and Biotechnology Center, Nagoya University, Nagoya, 464-8601 Japan
3 RIKEN Plant Science Center, Tsurumi, Yokohama, 230-0045 Japan
* Corresponding author: E-mail, satohshi{at}sakura.cc.tsukuba.ac.jp; Fax, +81-29-853-4579.
Plants alter the architecture of their root systems to adapt to the environment by modulating post-embryonic (lateral and adventitious) root formation and growth. To understand better the genetic basis of this regulation, we screened ethylmethane sulfonate-mutagenized lines of Arabidopsis thaliana for adventitious rooting mutants. One mutant showed retardation of the primary root growth, no production of lateral roots and enhanced formation of adventitious roots. Mapping and genetic complementation revealed that this mutant named wooden leg-3 (wol-3) was an allele of ARABIDOPSIS HISTIDINE KINASE 4 (AHK4), a locus known to encode a cytokinin receptor. Although the vascular system of the primary root and hypocotyl in the wol-3 mutant was aborted, that of the adventitious roots was normally developed. In the hypocotyl of the wol-3 mutant, auxin signals accumulated around the aborted vascular system. The application of auxin to primary roots induced lateral root formation in the wol-3 mutant. Transport of radiolabeled auxin from the top of the hypocotyl to the primary root was inhibited in wol-3. Although only a single amino acid alteration had occurred in AHK4, the root morphology in the wol-3 mutant was quite similar to that in the ahk2 ahk3 ahk4 triple mutant, which is a loss-of-function mutant of the three cytokinin receptors. This implies that the functional disturbance of AHK4 affects the function of the other receptors. Our results suggest that cytokinin receptors are necessary for the formation of auxin-transporting vascular tissues in the hypocotyl, but not in adventitious roots.
4 Present address: RIKEN Plant Science Center, Tsurumi, Yokohama, 230-0045 Japan
(Received July 23, 2005; Accepted December 6, 2005)
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