1. ¹Key Laboratory of the Ministry of Education for Plant Developmental Biology, College of Life Sciences, Wuhan University, Wuhan 430072, China
2. ²China-UK HUST-R Res Genetic Engineering and Genomics Joint Laboratory, Huazhong University of Science and Technology, Wuhan 430074, China

Correspondence: Guang Cun He, Tel: +86-27-87641314; Fax: +86-27-68752327; E-mail: gche@whu.edu.cn; Yun Chun Song, E-mail: songyc1936@yahoo.com.cn

^*These two authors contributed equally to this paper

Received 20 May 2005; Revised 19 September 2005; Accepted 13 October 2005.

Abstract

The genomic structures of Oryza sativa (A genome) and O. meyeriana (G genome) were comparatively studied using bicolor genomic in situ hybridization (GISH). GISH was clearly able to discriminate between the chromosomes of O. sativa and O. meyeriana in the interspecific F₁ hybrids without blocking DNA, and co-hybridization was hardly detected. The average mitotic chromosome length of O. meyeriana was found to be 1.69 times that of O. sativa. A comparison of 4,6-diamidino-2-phenylindole staining showed that the chromosomes of O. meyeriana were more extensively labelled, suggesting that the G genome is amplified with more repetitive sequences than the A genome. In interphase nuclei, 9-12 chromocenters were normally detected and nearly all the chromocenters constituted the G genome-specific DNA. More and larger chromocenters formed by chromatin compaction corresponding to the G genome were detected in the hybrid compared with its parents. During pachytene of the F₁ hybrid, most chromosomes of A and G did not synapse each other except for 1-2 chromosomes paired at the end of their arms. At meiotic metaphase I, three types of chromosomal associations, i.e. O. sativa-O. sativa (A-A), O. sativa-O. meyeriana (A-G) and O. meyeriana-O. meyeriana (G-G), were observed in the F₁ hybrid. The A-G chromosome pairing configurations included bivalents and trivalents. The results provided a foundation toward studying genome organization and evolution of O. meyeriana.