Rice, one of the world's most important food plants, has important syntenic relationships with the other cereal species and is a model plant for the grasses. Here we present a map-based, finished quality sequence that covers 95% of the 389 Mb genome, including virtually all of the euchromatin and two complete centromeres. A total of 37,544 nontransposable-element-related protein-coding genes were identified, of which 71% had a putative homologue in Arabidopsis. In a reciprocal analysis, 90% of the Arabidopsis proteins had a putative homologue in the predicted rice proteome. Twenty-nine per cent of the 37,544 predicted genes appear in clustered gene families. The number and classes of transposable elements found in the rice genome are consistent with the expansion of syntenic regions in the maize and sorghum genomes. We find evidence for widespread and recurrent gene transfer from the organelles to the nuclear chromosomes. The map-based sequence has proven useful for the identification of genes underlying agronomic traits. The additional single-nucleotide polymorphisms and simple sequence repeats identified in our study should accelerate improvements in rice production.

viruses were injected to follicles on both wings for later studies. Chickens were raised in cages and observed on a daily basis over a two-month period. The regenerated feathers were plucked and examined with a dissection or scanning electron micrograph microscope for abnormalities compared with normal primary remiges. Histology and in situ hybridizationParaffin sections (5 mm) were stained with haematoxylin and eosin or prepared for in situ hybridization following routine procedures 26 . Cryostat sections (10 mm) were stained with X-gal. TUNEL staining was performed using a kit (Roche). Nonradioactive wholemount or section in situ hybridization or section in situ hybridization was performed according to the protocol described 22,26 . After hybridization, sections were incubated with an antidigoxigenin Fab conjugated to alkaline phosphatase (Boehringer Mannheim). Colour was detected by incubating with a Boehringer Mannheim purple substrate (Roche).

Understanding the organization of eukaryotic centromeres has both fundamental and applied importance because of their roles in chromosome segregation, karyotypic stability, and artificial chromosome-based cloning and expression vectors. Using clone-by-clone sequencing methodology, we obtained the complete genomic sequence of the centromeric region of rice (Oryza sativa) chromosome 8. Analysis of 1.97 Mb of contiguous nucleotide sequence revealed three large clusters of CentO satellite repeats (68.5 kb of 155-bp repeats) and >220 transposable element (TE)-related sequences; together, these account for~60% of this centromeric region. The 155-bp repeats were tandemly arrayed head to tail within the clusters, which had different orientations and were interrupted by TE-related sequences. The individual 155-bp CentO satellite repeats showed frequent transitions and transversions at eight nucleotide positions. The 40 TE elements with highly conserved sequences were mostly gypsy-type retrotransposons. Furthermore, 48 genes, showing high BLAST homology to known proteins or to rice full-length cDNAs, were predicted within the region; some were close to the CentO clusters. We then performed a genome-wide survey of the sequences and organization of CentO and RIRE7 families. Our study provides the complete sequence of a centromeric region from either plants or animals and likely will provide insight into the evolutionary and functional analysis of plant centromeres.

;We developed seven Q-chromosome-specific DNA markers in Nicotiana tabacum by random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) analysis using two hybrid lines, and we were able to identify tobacco monosomic plants among F 1 progeny derived from the cross N. tabacum Haplo-Q × N. tabacum cv. Samsun NN using Q-chromosome-specific DNA markers. Based on the results, we discuss the roles of the Q chromosome in embryo sac development and embryogenesis. Here, we propose a new method for identifying DNA markers for a particular chromosome in the genus Nicotiana.