1. Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, New York 11724, USA
2. Present address: Department of Plant Production, University of Milan, Via Celoria 2, 20133 Milan, Italy

Correspondence to: David Jackson Email: jacksond@cshl.edu

Abstract

Phyllotaxy describes the geometric pattern of leaves and flowers, and has intrigued botanists and mathematicians for centuries^{1, 2}. How these patterns are initiated is poorly understood, and this is partly due to the paucity of mutants³. Signalling by the plant hormone auxin appears to determine the site of leaf initiation; however, this observation does not explain how distinct patterns of phyllotaxy are initiated⁴. abphyl1 (abph1) mutants of maize initiate leaves in a decussate pattern (that is, paired at 180°), in contrast to the alternating or distichous phyllotaxy observed in wild-type maize and other grasses⁵. Here we show that ABPH1 is homologous to two-component response regulators and is induced by the plant hormone cytokinin. ABPH1 is expressed in the embryonic shoot apical meristem, and its spatial expression pattern changes rapidly with cytokinin treatment. We propose that ABPH1 controls phyllotactic patterning by negatively regulating the cytokinin-induced expansion of the shoot meristem, thereby limiting the space available for primordium initiation at the apex.

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