Arabidopsis KNOXI proteins activate cytokinin biosynthesis

Osnat Yanai, Eilon Shani, Karel Dolezal, Petr Tarkowski, Robert Sablowski, Goran Sandberg, Alon Samach, Naomi Ori*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

429 Scopus citations


Plant architecture is shaped through the continuous formation of organs by meristems [1]. Class I KNOTTED1-like homeobox (KNOXI) genes are expressed in the shoot apical meristem (SAM) and are required for SAM maintenance [2-6]. KNOXI proteins and cytokinin, a plant hormone intimately associated with the regulation of cell division [7, 8], share overlapping roles, such as meristem maintenance and repression of senescence [2, 9-11], but their mechanistic and hierarchical relationship have yet to be defined. Here, we show that activation of three different KNOXI proteins using an inducible system resulted in a rapid increase in mRNA levels of the cytokinin biosynthesis gene isopentenyl transferase 7 (AtIPT7) and in the activation of ARR5, a cytokinin response factor. We further demonstrate a rapid and dramatic increase in cytokinin levels following activation of the KNOXI protein SHOOT MERISTEMLESS (STM). Application of exogenous cytokinin or expression of a cytokinin biosynthesis gene through the STM promoter partially rescued the stm mutant. We conclude that activation of cytokinin biosynthesis mediates KNOXI function in meristem maintenance. KNOXI proteins emerge as central regulators of hormone levels in plant meristems.

Original languageAmerican English
Pages (from-to)1566-1571
Number of pages6
JournalCurrent Biology
Issue number17
StatePublished - 6 Sep 2005

Bibliographical note

Funding Information:
We thank Veronique Pautot for the KNAT2-GR seeds, Joe Keiber for the ARR5:GUS and ARR5:GFP seeds, Yuval Eshed for the STM:LhG4 and OP:IPT seeds, Arnon Brand for the meristem drawing, and Neti Sirding for help with the SEM. We are grateful to Sarah Hake, Zach Adam, David Weiss, Yuval Eshed, Robert Fluhr, Guido Sessa, and members of the Ori laboratory for fruitful discussions and critical reading of the manuscript, and to M. Tsiantis for sharing and discussing unpublished results. This work was supported by grants from the U.S.-Israel Binational Science Foundation (no. 2000109) and the U.S.-Israel Binational Agricultural Research and Development fund (BARD, no. IS-3453-03).


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