A molecular-marker linkage map has been constructed for perennial ryegrass (Lolium perenne L.) using a one-way pseudo-testcross population based on the mating of a multiple heterozygous individual with a doubled haploid genotype. RFLP, AFLP, isoenzyme, and EST data from four collaborating laboratories within the International Lolium Genome Initiative were combined to produce an integrated genetic map containing 240 loci covering 811 cM on seven linkage groups. The map contained 124 codominant markers, of which 109 were heterologous anchor RFLP probes from wheat, barley, oat, and rice, allowing comparative relationships between perennial ryegrass and other Poaceae species to be inferred. The genetic maps of perennial ryegrass and the Triticeae cereals are highly conserved in terms of synteny and colinearity. This observation was supported by the general agreement of the syntenic relationships between perennial ryegrass, oat, and rice and those between the Triticeae and these species. A lower level of synteny and colinearity was observed between perennial ryegrass and oat compared with the Triticeae, despite the closer taxonomic affinity between these species. It is proposed that the linkage groups of perennial ryegrass be numbered in accordance with these syntenic relationships, to correspond to the homoeologous groups of the Triticeae cereals.Key words: Lolium perenne, genetic linkage map, RFLP, AFLP, conserved synteny.Résumé : Une carte génétique composée de marqueurs moléculaires a été produite pour l'ivraie vivace (Lolium perenne L.) à l'aide d'une population issue d'un pseudo-testcross unidirectionnel. Les parents étaient, d'une part, un individu multiple hétérozygote et, d'autre part, un génotype haploïde doublé. Des données pour des marqueurs RFLP, AFLP, isoenzymatiques ainsi que des EST ont été contribuées par quatre laboratoires faisant partie du « International Lolium Genome Initiative (ILGI) ». Ces données ont été combinées pour produire une carte génétique intégrée comprenant 240 locus, formant sept groupes de liaison et s'étendant sur 811 cM. La carte compte 124 marqueurs codominants dont 169 sont des sondes-repères RFLP hétérologues provenant du blé, de l'orge, de l'avoine ou du riz. Ces sondes permettent d'examiner les relations entre l'ivraie vivace et d'autres espèces de graminées. Les cartes génétiques de l'ivraie vivace et des céréales de la tribu des hordées sont très conservées en termes de synténie et de colinéarité. Cette conclusion s'appuie sur une concordance générale au niveau des relations de synténie entre l'ivraie vivace, l'avoine et le riz ainsi qu'entre les hordées et ces espèces. Un plus faible niveau de synténie et de colinéarité a été observé entre l'ivraie vivace et l'avoine par rapport aux hordées, malgré la proximité taxinomique entre ces espèces. Il est suggéré que les groupes de liaison chez l'ivraie vivace soient numérotés en fonction des relations de synténie de façon à correspondre aux groupes d'homéologues chez les céréales.

A key gene involved in plant senescence, mutations of which partially disable chlorophyll catabolism and confer stay-green leaf and cotyledon phenotypes, has been identified in Pisum sativum, Arabidopsis thaliana, and Festuca pratensis by using classical and molecular genetics and comparative genomics. A stay-green locus in F. pratensis is syntenically equivalent to a similar stay-green locus on rice chromosome 9. Functional testing in Arabidopsis of a homolog of the rice candidate gene revealed (i) senescence-associated gene expression and (ii) a stay-green phenotype after RNA interference silencing. Genetic mapping in pea demonstrated cosegregation with the yellow/green cotyledon polymorphism (I/i) first reported by Gregor Mendel in 1866.

SummaryDespite some notable successes, only a fraction of the genetic variation available in wild relatives has been utilized to produce superior wheat varieties. This is as a direct result of the lack of availability of suitable high‐throughput technologies to detect wheat/wild relative introgressions when they occur. Here, we report on the use of a new SNP array to detect wheat/wild relative introgressions in backcross progenies derived from interspecific hexaploid wheat/Ambylopyrum muticum F1 hybrids. The array enabled the detection and characterization of 218 genomewide wheat/Am. muticum introgressions, that is a significant step change in the generation and detection of introgressions compared to previous work in the field. Furthermore, the frequency of introgressions detected was sufficiently high to enable the construction of seven linkage groups of the Am. muticum genome, thus enabling the syntenic relationship between the wild relative and hexaploid wheat to be determined. The importance of the genetic variation from Am. muticum introduced into wheat for the development of superior varieties is discussed.

As part of an initiative to develop Brachypodium distachyon as a genomic ''bridge'' species between rice and the temperate cereals and grasses, a BAC library has been constructed for the two diploid (2n ¼ 2x ¼ 10) genotypes, ABR1 and ABR5. The library consists of 9100 clones, with an approximate average insert size of 88 kb, representing 2.22 genome equivalents. To validate the usefulness of this species for comparative genomics and gene discovery in its larger genome relatives, the library was screened by PCR using primers designed on previously mapped rice and Poaceae sequences. Screening indicated a degree of synteny between these species and B. distachyon, which was confirmed by fluorescent in situ hybridization of the marker-selected BACs (BAC landing) to the 10 chromosome arms of the karyotype, with most of the BACs hybridizing as single loci on known chromosomes. Contiguous BACs colocalized on individual chromosomes, thereby confirming the conservation of genome synteny and proving that B. distachyon has utility as a temperate grass model species alternative to rice.

The genetic control of induction to flowering has been studied extensively in both model and crop species because of its fundamental biological and economic significance. An ultimate aim of many of these studies has been the application of the understanding of control of flowering that can be gained from the study of model species, to the improvement of crop species. The present study identifies a region of genetic synteny between rice and Lolium perenne, which contains the Hd3 heading-date QTL in rice and a major QTL, accounting for up to 70% of the variance associated with heading date in L. perenne. The identification of synteny between rice and L. perenne in this region demonstrates the direct applicability of the rice genome to the understanding of biological processes in other species. Specifically, this syntenic relationship will greatly facilitate the genetic dissection of aspects of heading-date induction by enabling the magnitude of the genetic component of the heading-date QTL in L. perenne to be combined with the sequencing and annotation information from the rice genome.

Ougham, H. J., Hortensteiner, S., Armstead, I. P., Donnison, I. S., King, I. P., Thomas, Howard, Mur, L. A. J. (2008). The control of chlorophyll catabolism and the status of yellowing as a biomarker of leaf senescence. Plant Biology, 10, (Supplement 1), pp. 4-14 IMPF: 01.94 RONO: 1310 3001The pathway of chlorophyll catabolism during leaf senescence is known in a fair amount of biochemical and cell biological detail. In the last few years, genes encoding a number of the catabolic enzymes have been characterized, including the key ring-opening activities, phaeophorbide a oxygenase (PaO) and red chlorophyll catabolite reductase (RCCR). Recently, a gene that modulates disassembly of chlorophyll?protein complexes and activation of pigment ring-opening has been isolated by comparative mapping in monocot species, positional cloning exploiting rice genomics resources and functional testing in Arabidopsis. The corresponding gene in pea has been identified as Mendel's I locus (green/yellow cotyledons). Mutations in this and other chlorophyll catabolic genes have significant consequences, both for the course of leaf senescence and senescence-like stress responses, notably hypersensitivity to pathogen challenge. Loss of chlorophyll can occur via routes other than the PaO/RCCR pathway, resulting in changes that superficially resemble senescence. Such 'pseudosenescence' responses tend to be pathological rather than physiological and may differ from senescence in fundamental aspects of biochemistry and regulation.Peer reviewe

Armstead, I. P., Donnison, I. S., Aubry, S., Harper, J. A., Hortensteiner, S., James, C. L., Mani, J., Moffet, M., Ougham, H. J., Roberts, L. A., Thomas, A., Weeden, N., Thomas, Howard, King, I. P. (2006). From crop to model to crop: identifying the genetic basis of the staygreen mutation in the Lolium/Festuca forage and amenity grasses. New Phytologist, 172 (4), 592-597.Peer reviewe

We report on the evaluation of a novel grass hybrid that provides efficient forage production and could help mitigate flooding. Perennial ryegrass (Lolium perenne) is the grass species of choice for most farmers, but lacks resilience against extremes of climate. We hybridised L. perenne onto a closely related and more stress-resistant grass species, meadow fescue Festuca pratensis. We demonstrate that the L. perenne × F. pratensis cultivar can reduce runoff during the events by 51% compared to a leading UK nationally recommended L. perenne cultivar and by 43% compared to F. pratensis over a two year field experiment. We present evidence that the reduced runoff from this Festulolium cultivar was due to intense initial root growth followed by rapid senescence, especially at depth. Hybrid grasses of this type show potential for reducing the likelihood of flooding, whilst providing food production under conditions of changing climate.