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Summary: The rice heterochronic gene SUPERNUMERARY BRACT
regulates the transition from spikelet meristem to floral
meristem
Dong-Yeon Lee, Jinwon Lee, Sunok Moon, Soung Young Park and Gynheung An*
National Research Laboratory of Plant Functional Genomics, Division of Molecular and Life Sciences, Pohang University of
Science and Technology (POSTECH), Pohang 790-784, Korea
Received 18 July 2006; revised 24 August 200x; accepted 30 August 2006.
*For correspondence (fax þ82 54 279 0659; e-mail genean@postech.ac.kr).
Summary
Regulating the transition of meristem identity is a critical step in reproductive development. After the shoot
apical meristem (SAM) acquires inflorescence meristem identity, it goes through a sequential transition to
second- and higher-order meristems that can eventually give rise to floral organs. Despite ample information
on the molecular mechanisms that control the transition from SAM to inflorescence meristems, little is
known about the mechanism for inflorescence development, especially in monocots. Here, we report the
identification of the SUPERNUMERARY BRACT (SNB) gene controlling the transition from spikelet meristem
to floral meristem and the floral organ development. This gene encodes a putative transcription factor
carrying two AP2 domains. The SNB:GFP fusion protein is localized to the nucleus. SNB is expressed in all the
examined tissues, but most strongly in the newly emerging spikelet meristems. In SNB knockout plants, the
transition from spikelet meristems to floral meristems is delayed, resulting in the production of multiple
rudimentary glumes in an alternative phyllotaxy. The development of additional bracts interferes with
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