For gametophytic apomixis, the embryo devel ops from an unreduced egg in an embryo sac derived through mitosis of either a somatic nucellar cell or the megaspore mother cell. In apospory, meiosis either does not complete or its pro ducts degenerate while aposporous initials develop from one or more somatic nucellar cells. Both genotypes chosen for the present study are aposporous with the trait conferred by genetic elements from Pennisetum squamulatum. Aposporous P. squamulatum has four nucleate embryo sacs that lack antipodals. Aposp ory in this species is inherited as a dominant Mendelian trait and is associated with an approximately 50 Mb, heterochromatic and hemizygous chromosomal region designated the Apospory Specific Genomic Region.
Many transcriptional approaches to discover the regu latory mechanisms and downstream Inhibitors,Modulators,Libraries effects associated with apomixis in many species have been undertaken. In Brachiaria, differential display applied to apomictic and sexual ovaries at anthesis yielded two apomixis specific fragments while a study on earlier sporogenesis and gametogenesis stages identified eleven differentially Inhibitors,Modulators,Libraries expressed fragments. In Paspalum notatum, GSK-3 three expressed sequence tags, all highly similar in sequence, showed differential expression in flowers between apomictic and sexual F1 individuals after aposp ory initiation. An additional 65 genes were identi fied as differentially expressed between sexual and aposporous plants. cDNA AFLP analysis in Paspa lum simplex yielded transcripts linked to the apomixis controlling locus.
Many of these Inhibitors,Modulators,Libraries linked fragments showed stop codons and frameshift mutations, suggest ing that they are pseudogenes. cDNA AFLP was also applied to identify apomixis candidate genes in Poa pratensis where 179 transcript derived fragments from spikelets showed qualitative and quantitative expression differences between apomictic and sexual genotypes. The full length sequences Inhibitors,Modulators,Libraries of two genes of interest, PpSERK and APOSTART were obtained and their temporal and spatial expression patterns were assessed by reverse transcription polymerase chain reaction and in situ hybridization, respectively. While neither one of these two candidate genes showed apo mixis or sexual specific expression, quantitative differ ences in expression between apomictic and sexual genotypes were observed.
One apomixis specific gene was identified from a Panicum maximum ovule cDNA library and shown to be expressed in both aposporous initials and embryos at four days after anthesis. Additional genes have been identified in Panicum through microarray and quantitative RT PCR analysis. In Pennisetum ciliare, differential display and suppression subtractive hybridi zation were used to identify gene expression differences in ovaries of sexual and apomictic accessions.
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