Direct control of shoot meristem activity by a cytokinin-activating enzyme

Kurakawa, Takashi
Ueda, Nanae
Maekawa, Masahiko
Kobayashi, Kaoru
Kojima, Mikiko
Nagato, Yasuo
Sakakibara, Hitoshi
Kyozuka, Junko

¹Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi, Bunkyo, Tokyo 113-8652, Japan. ²RIKEN Plant Science Center, Tsurumi, Yokohama 230-0045, Japan.
³Research Institute for Bioresources, Okayama University, Kurashiki, Okayama, 710-0046 Japan.

doi:10.1038/nature05504

*These two authors contributed equally to this work.

Received 19 October; accepted 1 December 2006.

Supplementary Information is linked to the online version of the paper at www.nature.com/nature.

Author Information Genbank accession numbers are as follows: LOG (AK071695), LOC_Os01g51210 (AK061091), LOC_Os05g46360 (AK068633), LOC_Os03g49050 (AC123974), LOC_Os09g37540 (AK062595), LOC_Os05g51390 (AK242659), LOC_Os03g64070 (AK061341), LOC_Os03g01880 (AK099538), LOC_Os10g33900 (AK108805), LOC_Os02g41770 (AP005000), LOC_Os04g43840 (AK069293), At2g28305 (NM_128389), At2g35990 (NM_129158), At2g37210 (NM_129277), At3g53450 (NM_115205), AT4G35190 (NM_119685), At5g03270 (NM_120405), At5g06300 (NM_120713), At5g11950 (NM_121233) and At5g26140 (NM_122515). Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests. Correspondence and requests for materials should be addressed to J. K. ([email protected]) or H.S. ([email protected]).

Nature 445(7128):p 652-655, February 8, 2007.

The growth of plants depends on continuous function of the meristems. Shoot meristems are responsible for all the post-embryonic aerial organs, such as leaves, stems and flowers. It has been assumed that the phytohormone cytokinin has a positive role in shoot meristem function. A severe reduction in the size of meristems in a mutant that is defective in all of its cytokinin receptors has provided compelling evidence that cytokinin is required for meristem activity. Here, we report a novel regulation of meristem activity, which is executed by the meristem-specific activation of cytokinins. TheLONELY GUY (LOG)gene of rice is required to maintain meristem activity and its loss of function causes premature termination of the shoot meristem.LOGencodes a novel cytokinin-activating enzyme that works in the final step of bioactive cytokinin synthesis. Revising the long-held idea of multistep reactions, LOG directly converts inactive cytokinin nucleotides to the free-base forms, which are biologically active, by its cytokinin-specific phosphoribohydrolase activity.LOGmessenger RNA is specifically localized in shoot meristem tips, indicating the activation of cytokinins in a specific developmental domain. We propose the fine-tuning of concentrations and the spatial distribution of bioactive cytokinins by a cytokinin-activating enzyme as a mechanism that regulates meristem activity.