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DEVELOPMENT AND HORMONE ACTION

L1 Division and Differentiation Patterns Influence Shoot Apical Meristem Maintenance¹

Section of Plant Biology, University of California, Davis, California 95616

Plant development requires regulation of both cell division and differentiation. The class 1 KNOTTED1-like homeobox (KNOX) genes such as knotted1 (kn1) in maize (Zea mays) and SHOOTMERISTEMLESS in Arabidopsis (Arabidopsis thaliana) play a role in maintaining shoot apical meristem indeterminacy, and their misexpression is sufficient to induce cell division and meristem formation. KNOX overexpression experiments have shown that these genes interact with the cytokinin, auxin, and gibberellin pathways. The L1 layer has been shown to be necessary for the maintenance of indeterminacy in the underlying meristem layers. This work explores the possibility that the L1 affects meristem function by disrupting hormone transport pathways. The semidominant Extra cell layers1 (Xcl1) mutation in maize leads to the production of multiple epidermal layers by overproduction of a normal gene product. Meristem size is reduced in mutant plants and more cells are incorporated into the incipient leaf primordium. Thus, Xcl1 may provide a link between L1 division patterns, hormonal pathways, and meristem maintenance. We used double mutants between Xcl1 and dominant KNOX mutants and showed that Xcl1 suppresses the Kn1 phenotype but has a synergistic interaction with gnarley1 and rough sheath1, possibly correlated with changes in gibberellin and auxin signaling. In addition, double mutants between Xcl1 and crinkly4 had defects in shoot meristem maintenance. Thus, proper L1 development is essential for meristem function, and XCL1 may act to coordinate hormonal effects with KNOX gene function at the shoot apex.

² Present address: Institute for Plant Biology, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Neelima Sinha (nrsinha{at}ucdavis.edu).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.076075.

^* Corresponding author; e-mail nrsinha{at}ucdavis.edu; fax 530–752–5410.

Received December 21, 2005; returned for revision May 21, 2006; accepted May 25, 2006.

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