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MBE Advance Access published online on May 2, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn105
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Article

Duplication and functional diversification of HAP3 genes leading to the origin of the seed-developmental regulatory gene, LEAFY COTYLEDON1 (LEC1), in non-seed plant genomes

Zengyan Xie1, Xia Li1, Beverley J. Glover2, Shunong Bai1, Guang-Yuan Rao1, Jingchu Luo1 and Ji Yang3,*

1 College of Life Sciences, Peking University, Beijing 100871, China
2 Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK
3 Centre for Evolutionary Biology and Institute of Biodiversity Science, Fudan University, Shanghai 200433, China

* Correspondence to: Ji Yang, School of Life Sciences, Fudan University, Shanghai 200433, P R China, Phone: +86 (21) 65643494, Email: jiyang{at}fudan.edu.cn

Received for publication October 25, 2007. Revision received February 1, 2008. Revision received April 9, 2008. Accepted for publication April 29, 2008.

The HAP3 gene encodes a subunit of the CCAAT-box binding factor (CBF), a highly conserved trimeric activator that recognizes and binds the ubiquitous CCAAT promoter element with high affinity. Two types of HAP3 gene have been identified in plant genomes. The LEC1-type HAP3 genes encode a functionally specialized subunit of CBF, which is expressed specifically in developing seeds. In contrast, most non-LEC1-type HAP3 genes are expressed in various tissues. It has been proposed that the LEC1-type HAP3genes originated from the duplication and functional divergence of non-LEC1-type HAP3 genes. However, it is not yet known when this duplication event took place or whether the LEC1-type HAP3genes appeared at the same time as the origin of seed plants. Here we describe a comprehensive comparison of the duplication patterns of HAP3 genes in different plant genomes. We recognize a major expansion of the HAP3 gene family accompanying the origin and early diversification of land plants, and postulate that retrotransposition and other mechanisms of gene duplication have been involved in the expansion of the plant HAP3 gene family. We provide evidence that the LEC1-type HAP3genes originated in non-seed vascular plant genomes, and demonstrate that they are inductively expressed under drought stress in non-seed plants. These genes, however, were recruited to a novel regulatory network in the early stages of seed plant evolution and steadily expressed during seed development and maturation.

Key Words: HAP3 gene family • lineage-specific duplication • LEC1 • gene origin


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