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


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 languageEnglish
Pages (from-to)1566-1571
Number of pages6
JournalCurrent Biology
Issue number17
StatePublished - 6 Sep 2005
Externally publishedYes


FundersFunder number
United States - Israel Binational Agricultural Research and Development Fund
United States-Israel Binational Science Foundation2000109


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