Cenchrus
Pennisetum
Apomixis
Delineation by fluorescence in situ hybridization of a single hemizygous chromosomal region associated with aposporous embryo sac formation in Pennisetum squamulatum and Cenchrus ciliaris. (1/5)
Apomixis is a means of asexual reproduction by which plants produce embryos without meiosis and fertilization; thus the embryo is of clonal, maternal origin. We previously reported molecular markers showing no recombination with the trait for aposporous embryo sac development in Pennisetum squamulatum and Cenchrus ciliaris, and the collective single-dose alleles defined an apospory-specific genomic region (ASGR). Fluorescence in situ hybridization (FISH) was used to confirm that the ASGR is a hemizygous genomic region and to determine its chromosomal position with respect to rDNA loci and centromere repeats. We also documented chromosome transmission from P. squamulatum in several backcrosses (BCs) with P. glaucum using genomic in situ hybridization (GISH). One to three complete P. squamulatum chromosomes were detected in BC(6), but only one of the three hybridized with the ASGR-linked markers. In P. squamulatum and in all BCs examined, the apospory-linked markers were located in the distal region of the short arm of a single chromosome. All alien chromosomes behaved as univalents during meiosis and segregated randomly in BC(3) and later BC generations, but presence of the ASGR-carrier chromosome alone was sufficient to confer apospory. FISH results support our hypotheses that hemizygosity, proximity to centromeric sequences, and chromosome structure may all play a role in low recombination in the ASGR. (+info)A segment of the apospory-specific genomic region is highly microsyntenic not only between the apomicts Pennisetum squamulatum and buffelgrass, but also with a rice chromosome 11 centromeric-proximal genomic region. (2/5)
Bacterial artificial chromosome (BAC) clones from apomicts Pennisetum squamulatum and buffelgrass (Cenchrus ciliaris), isolated with the apospory-specific genomic region (ASGR) marker ugt197, were assembled into contigs that were extended by chromosome walking. Gene-like sequences from contigs were identified by shotgun sequencing and BLAST searches, and used to isolate orthologous rice contigs. Additional gene-like sequences in the apomicts' contigs were identified by bioinformatics using fully sequenced BACs from orthologous rice contigs as templates, as well as by interspecies, whole-contig cross-hybridizations. Hierarchical contig orthology was rapidly assessed by constructing detailed long-range contig molecular maps showing the distribution of gene-like sequences and markers, and searching for microsyntenic patterns of sequence identity and spatial distribution within and across species contigs. We found microsynteny between P. squamulatum and buffelgrass contigs. Importantly, this approach also enabled us to isolate from within the rice (Oryza sativa) genome contig Rice A, which shows the highest microsynteny and is most orthologous to the ugt197-containing C1C buffelgrass contig. Contig Rice A belongs to the rice genome database contig 77 (according to the current September 12, 2003, rice fingerprint contig build) that maps proximal to the chromosome 11 centromere, a feature that interestingly correlates with the mapping of ASGR-linked BACs proximal to the centromere or centromere-like sequences. Thus, relatedness between these two orthologous contigs is supported both by their molecular microstructure and by their centromeric-proximal location. Our discoveries promote the use of a microsynteny-based positional-cloning approach using the rice genome as a template to aid in constructing the ASGR toward the isolation of genes underlying apospory. (+info)Comparative physical mapping of the apospory-specific genomic region in two apomictic grasses: Pennisetum squamulatum and Cenchrus ciliaris. (3/5)
In gametophytic apomicts of the aposporous type, each cell of the embryo sac is genetically identical to somatic cells of the ovule because they are products of mitosis, not of meiosis. The egg of the aposporous embryo sac follows parthenogenetic development into an embryo; therefore, uniform progeny result even from heterozygous plants, a trait that would be valuable for many crop species. Attempts to introgress apomixis from wild relatives into major crops through traditional breeding have been hindered by low or no recombination within the chromosomal region governing this trait (the apospory-specific genomic region or ASGR). The lack of recombination also has been a major obstacle to positional cloning of key genes. To further delineate and characterize the nonrecombinant ASGR, we have identified eight new ASGR-linked, AFLP-based molecular markers, only one of which showed recombination with the trait for aposporous embryo sac development. Bacterial artificial chromosome (BAC) clones identified with the ASGR-linked AFLPs or previously mapped markers, when mapped by fluorescence in situ hybridization in Pennisetum squamulatum and Cenchrus ciliaris, showed almost complete macrosynteny between the two apomictic grasses throughout the ASGR, although with an inverted order. A BAC identified with the recombinant AFLP marker mapped most proximal to the centromere of the ASGR-carrier chromosome in P. squamulatum but was not located on the ASGR-carrier chromosome in C. ciliaris. Exceptional regions where synteny was disrupted probably are nonessential for expression of the aposporous trait. The ASGR appears to be maintained as a haplotype even though its position in the genome can be variable. (+info)Sequence analysis of bacterial artificial chromosome clones from the apospory-specific genomic region of Pennisetum and Cenchrus. (4/5)
(+info)Phylogenetic studies favour the unification of Pennisetum, Cenchrus and Odontelytrum (Poaceae): a combined nuclear, plastid and morphological analysis, and nomenclatural combinations in Cenchrus. (5/5)
(+info)"Cenchrus" is a genus of plants in the family Poaceae, also known as the grass family. It includes several species of plants commonly known as sandburrs or sandspurs because of their characteristic burrs that are covered in sharp spines. These burrs can easily become attached to fur, feathers, or clothing, making them a nuisance in many environments. Some common species in this genus include C. echinatus (jointed goatgrass), C. longispinus (longspine sandbur), and C. spinifex (sea oats).
I'm sorry for any confusion, but "Pennisetum" is not a medical term. It is the name of a genus of plants in the grass family, also known as fountain grasses or feather grasses. They are often used in ornamental landscaping. If you have any questions about a medical term or concept, I'd be happy to help clarify!
Apomixis is a form of asexual reproduction in plants that involves the development of a seed without fertilization. It occurs through various mechanisms, such as agamospermy or parthenogenesis, where the embryo develops from an unfertilized egg cell or other cells within the ovule. This process bypasses the formation of gametes and meiosis, resulting in offspring that are genetically identical to the parent plant.
In agamospermy, the embryo sac develops without fertilization, and the chromosome number is maintained through mitotic divisions. In parthenogenesis, the egg cell develops into an embryo without being fertilized by a sperm cell. Apomixis can be advantageous for plant breeding as it allows for the rapid propagation of desirable traits and hybrids without the need for time-consuming and expensive traditional breeding methods. However, apomictic plants may also exhibit reduced genetic diversity, which can make them more susceptible to diseases and pests.
Poaceae is not a medical term but a taxonomic category, specifically the family name for grasses. In a broader sense, you might be asking for a medical context where knowledge of this plant family could be relevant. For instance, certain members of the Poaceae family can cause allergies or negative reactions in some people.
In a medical definition, Poaceae would be defined as:
The family of monocotyledonous plants that includes grasses, bamboo, and sedges. These plants are characterized by narrow leaves with parallel veins, jointed stems (called "nodes" and "internodes"), and flowers arranged in spikelets. Some members of this family are important food sources for humans and animals, such as rice, wheat, corn, barley, oats, and sorghum. Other members can cause negative reactions, like skin irritation or allergies, due to their silica-based defense structures called phytoliths.