Reticulate evolution in Panicum (Poaceae): the origin of tetraploid broomcorn millet, P. miliaceum.

Panicum miliaceum (broomcorn millet) is a tetraploid cereal, which was among the first domesticated crops, but is now a minor crop despite its high water use efficiency. The ancestors of this species have not been determined; we aimed to identify likely candidates within the genus, where phylogenies are poorly resolved. Nuclear and chloroplast DNA sequences from P. miliaceum and a range of diploid and tetraploid relatives were used to develop phylogenies of the diploid and tetraploid species. Chromosomal in situ hybridization with genomic DNA as a probe was used to characterize the genomes in the tetraploid P. miliaceum and a tetraploid accession of P. repens. In situ hybridization showed that half the chromosomes of P. miliaceum hybridized more strongly with labelled genomic DNA from P. capillare, and half with labelled DNA from P. repens. Genomic DNA probes differentiated two sets of 18 chromosomes in the tetraploid P. repens. Our phylogenetic data support the allotetraploid origin of P. miliaceum, with the maternal ancestor being P. capillare (or a close relative) and the other genome being shared with P. repens. Our P. repens accession was also an allotetraploid with two dissimilar but closely related genomes, the maternal genome being similar to P. sumatrense. Further collection of Panicum species, particularly from the Old World, is required. It is important to identify why the water-efficient P. miliaceum is now of minimal importance in agriculture, and it may be valuable to exploit the diversity in this species and its ancestors

Integration of genetic and physical maps of the Primula vulgaris S locus and localization by chromosome in situ hybridization

•Heteromorphic flower development in Primula is controlled by the S locus. The S locus genes, which control anther position, pistil length and pollen size in pin and thrum flowers, have not yet been characterized. We have integrated S-linked genes, marker sequences and mutant phenotypes to create a map of the P. vulgaris S locus region that will facilitate the identification of key S locus genes. We have generated, sequenced and annotated BAC sequences spanning the S locus, and identified its chromosomal location. •We have employed a combination of classical genetics and three-point crosses with molecular genetic analysis of recombinants to generate the map. We have characterized this region by Illumina sequencing and bioinformatic analysis, together with chromosome in situ hybridization. •We present an integrated genetic and physical map across the P. vulgaris S locus flanked by phenotypic and DNA sequence markers. BAC contigs encompass a 1.5-Mb genomic region with 1 Mb of sequence containing 82 S-linked genes anchored to overlapping BACs. The S locus is located close to the centromere of the largest metacentric chromosome pair. •These data will facilitate the identification of the genes that orchestrate heterostyly in Primula and enable evolutionary analyses of the S locus

Structure of the C1r-C1s interaction of the C1 complex of complement activation.

The multiprotein complex C1 initiates the classical pathway of complement activation on binding to antibody-antigen complexes, pathogen surfaces, apoptotic cells, and polyanionic structures. It is formed from the recognition subcomponent C1q and a tetramer of proteases C1r2C1s2 as a Ca2+-dependent complex. Here we have determined the structure of a complex between the CUB1-EGF-CUB2 fragments of C1r and C1s to reveal the C1r-C1s interaction that forms the core of C1. Both fragments are L-shaped and interlock to form a compact antiparallel heterodimer with a Ca2+ from each subcomponent at the interface. Contacts, involving all three domains of each protease, are more extensive than those of C1r or C1s homodimers, explaining why heterocomplexes form preferentially. The available structural and biophysical data support a model of C1r2C1s2 in which two C1r-C1s dimers are linked via the catalytic domains of C1r. They are incompatible with a recent model in which the N-terminal domains of C1r and C1s form a fixed tetramer. On binding to C1q, the proteases become more compact, with the C1r-C1s dimers at the center and the six collagenous stems of C1q arranged around the perimeter. Activation is likely driven by separation of the C1r-C1s dimer pairs when C1q binds to a surface. Considerable flexibility in C1s likely facilitates C1 complex formation, activation of C1s by C1r, and binding and activation of downstream substrates C4 and C4b-bound C2 to initiate the reaction cascade.Funding for this work was provided by the Medical Research Council (Grant G1000191/1, to R.W., P.C.E.M., and W.J.S.)

Genomes in the evolution of polyploid crop species and hybrids

Many of the world’s crop species are recent polyploids. The various genomes from the diploid ancestors (known or, often, unknown) interact, with variable effects on genome packaging and nuclear organization (together the nuclear architecture), chromosome stability and gene expression. This project used a comparative approach to understand the genome composition in polyploids, focusing on millets in the Panicum group, saffron Crocus, Brassica and Nicotiana. In situ hybridization using DNA probes was used to identify the chromosomes and antibodies to synaptonemal complex, DNA repair and chromatin structure proteins including histones, which allow the understanding of the modulation of chromosome behaviour depending on the ancestral origin of the chromosomes, were used. The ancestors of proso millet, P. miliaceum (2n=4x=36), were identified as P. capillare and being the same as one genome in the 4x P. repens by in situ hybridization and ITS sequencing. A cell fusion hybrid of Nicotiana x sanderae + N. debneyi was confirmed, with demonstration of chromosome loss, by IRAP markers and in situ hybridization. Saffron Crocus, Crocus sativus 2n=3x=24, was shown to not be an autopolyploid, but to include three genomes with somewhat different chromosomal and sequence characteristics. The alien lines of Brassica and Raphanus with the fertility restorer genes were identified with B. rapa carrying the two chromosomes of Raphanus carrying the fertility restorer genes. Furthermore, the meiotic pairing basis of the alien lines of Brassica and Orychophragmus was also observed which gives an insight into the meiotic pairing between two different species. The water stress resistant genes could be identified from Panicum and thus be utilized in better water usage of plants. It would be possible in future to develop a synthetic C. sativus and thus rescue its declining production around the world, thus improving its economic potential. The fertility restorer gene can now be introduced into the B. rapa species using various mutagens