www.newphytologist.org 239 Research Blackwell Publishing, Ltd. Identification of perennial ryegrass (Lolium perenne (L.)) and meadow fescue ( Festuca pratensis (Huds.)) candidate orthologous sequences to the rice Hd1(Se1) and barley HvCO1 CONSTANS-like genes through comparative mapping and microsynteny I. P. Armstead, L. Skøt, L. B. Turner, K. Skøt, I. S. Donnison, M. O. Humphreys and I. P. King Plant Genetics and Breeding Department, Institute of Grassland and Environmental Research, Aberystwyth, Ceredigion SY23 3EB, UK Summary • Microsynteny with rice and comparative genetic mapping were used to identify candidate orthologous sequences to the rice Hd1(Se1) gene in Lolium perenne and Festuca pratensis. •A F. pratensis bacterial artificial chromosome (BAC) library was screened with a marker (S2539) physically close to Hd1 in rice to identify the equivalent genomic region in F. pratensis . The BAC sequence was used to identify and map the same region in L. perenne. • Predicted protein sequences for L. perenne and F. pratensis Hd1 candidates (LpHd1 and FpHd1) indicated they were CONSTANS-like zinc finger proteins with 61– 62% sequence identity with rice Hd1 and 72% identity with barley HvCO1. LpHd1 and FpHd1 were physically linked in their respective genomes (< 4 kb) to marker S2539, which was mapped to L. perenne chromosome 7. • The identified candidate orthologues of rice Hd1 and barley HvCO1 in L. perenne and F. pratensis map to chromosome 7, a region of the L. perenne genome which has a degree of conserved genetic synteny both with rice chromosome 6, which contains Hd1 , and barley chromosome 7H, which contains HvCO1 . Key words: CONSTANS, Festuca ( Schedonorus ) pratensis (meadow fescue), flowering, Hd1, HvCO1, Lolium perenne (perennial ryegrass), LpCO, microsynteny. New Phytologist (2005) 167 : 239–247 © New Phytologist (2005) doi : 10.1111/j.1469-8137.2005.01392.x Author for correspondence: Ian Armstead Tel: +44 (0)1970 823108 Fax: +44 (0)1970 823242 Email: ian.armstead@bbsrc.ac.uk Received: 29 November 2004 Accepted: 17 January 2005 Introduction Comparative genetic mapping between plant species has established that there has been a recognizable conservation of genomic organization which reflects evolutionary relationships. This can be most clearly seen in the genetic analyses that have aligned the genomes of various grass species (Dunford et al., 1995; Moore et al., 1995; Gale & Devos, 1998; van Deynze et al ., 1998; Smilde et al ., 2001; Jones et al ., 2002). The publication of the complete genome sequences of rice (Goff et al., 2002) and Arabidopsis (Arabidopsis Genome Initiative, 2000) has allowed the description of these underlying syntenic relationships to be taken to a more detailed level through detailed annotations and comparative physical mapping of gene sequences (http://www.gramene.org; Sutton et al., 2003). While comprehensive microsyntenic relationships between model and crop species may soon become available for major crop species, this is unlikely to be true for other species, including the forage and amenity grasses of the Lolium/Festuca complex. For this latter group, the driver for the establishment of microsyntenic relationships with model species will be specific experimental aims. In forage and amenity grasses, one of these aims is to further our understanding of the processes that control the timing of the transition from vegetative to