http://hdl.handle.net/2440/7 Mon, 20 May 2013 06:44:25 GMT 2013-05-20T06:44:25Z http://hdl.handle.net/2440/77846 Title: Sporophytic ovule tissues modulate the initiation and progression of apomixis in Hieracium Author: Tucker, Matthew Robert; Okada, Takashi; Johnson, Susan D.; Takaiwa, Fumio; Koltunow, Anna Maria Grazyna Abstract: Apomixis in Hieracium subgenus Pilosella initiates in ovules when sporophytic cells termed aposporous initial (AI) cells enlarge near sexual cells undergoing meiosis. AI cells displace the sexual structures and divide by mitosis to form unreduced embryo sac(s) without meiosis (apomeiosis) that initiate fertilization-independent embryo and endosperm development. In some Hieracium subgenus Pilosella species, these events are controlled by the dominant LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP) loci. In H. praealtum and H. piloselloides, which both contain the same core LOA locus, the timing and frequency of AI cell formation is altered in derived mutants exhibiting abnormal funiculus growth and in transgenic plants expressing rolB which alters cellular sensitivity to auxin. The impact on apomictic and sexual reproduction was examined here when a chimeric RNAse gene was targeted to the funiculus and basal portions of the ovule, and also when polar auxin transport was inhibited during ovule development following N-1-naphthylphthalamic acid (NPA) application. Both treatments led to ovule deformity in the funiculus and distal parts of the ovule and LOA-dependent alterations in the timing, position, and frequency of AI cell formation. In the case of NPA treatment, this correlated with increased expression of DR5:GFP in the ovule, which marks the accumulation of the plant hormone auxin. Our results show that sporophytic information potentiated by funiculus growth and polar auxin transport influences ovule development, the initiation of apomixis, and the progression of embryo sac development in Hieracium. Signals associated with ovule pattern formation and auxin distribution or perception may influence the capacity of sporophytic ovule cells to respond to LOA. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77846 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77823 Title: Stem and gall forming nematodes Author: Subbotin, Sergei A.; Riley, Ian Timothy Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77823 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77737 Title: A breeding strategy to harness flavour diversity of Saccharomyces interspecific hybrids and minimize hydrogen sulphide production Author: Bizaj, Etjen; Cordente, Antonio G.; Bellon, Jennifer Rose; Raspor, Peter; Curtin, Christopher D.; Pretorius, Isak Stephanus Abstract: Industrial food-grade yeast strains are selected for traits that enhance their application in quality production processes. Wine yeasts are required to survive in the harsh environment of fermenting grape must, while at the same time contributing to wine quality by producing desirable aromas and flavors. For this reason, there are hundreds of wine yeasts available, exhibiting characteristics that make them suitable for different fermentation conditions and winemaking practices. As wine styles evolve and technical winemaking requirements change, however, it becomes necessary to improve existing strains. This becomes a laborious and costly process when the targets for improvement involve flavor compound production. Here, we demonstrate a new approach harnessing preexisting industrial yeast strains that carry desirable flavor phenotypes - low hydrogen sulfide (H(2) S) production and high ester production. A low-H(2) S Saccharomyces cerevisiae strain previously generated by chemical mutagenesis was hybridized independently with two ester-producing natural interspecies hybrids of S. cerevisiae and Saccharomyces kudriavzevii. Deficiencies in sporulation frequency and spore viability were overcome through use of complementary selectable traits, allowing successful isolation of several novel hybrids exhibiting both desired traits in a single round of selection. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77737 2011-12-31T13:30:00Z http://hdl.handle.net/2440/77681 Title: The genome sequence of the wine yeast VIN7 reveals an allotriploid hybrid genome with Saccharomyces cerevisiae and Saccharomyces kudriavzevii origins Author: Borneman, Anthony Richard; Desany, Brian; Riches, David; Affourtit, Jason P.; Forgan, Angus Henderson; Pretorius, Isak Stephanus; Egholm, Michael; Chambers, Paul J. Abstract: The vast majority of wine fermentations are performed principally by Saccharomyces cerevisiae. However, there are a growing number of instances in which other species of Saccharomyces play a predominant role. Interestingly, the presence of these other yeast species generally occurs via the formation of interspecific hybrids that contain genomic contributions from both S. cerevisiae and non-S. cerevisiae species. However, despite the large number of wine strains that are characterized at the genomic level, there remains limited information regarding the detailed genomic structure of hybrids used in winemaking. To address this, we describe the genome sequence of the thiol-releasing commercial wine yeast hybrid VIN7. VIN7 is shown to be an almost complete allotriploid interspecific hybrid that is comprised of a heterozygous diploid complement of S. cerevisiae chromosomes and a haploid Saccharomyces kudriavzevii genomic contribution. Both parental strains appear to be of European origin, with the S. cerevisiae parent being closely related to, but distinct from, the commercial wine yeasts QA23 and EC1118. In addition, several instances of chromosomal rearrangement between S. cerevisiae and S. kudriavzevii sequences were observed that may mark the early stages of hybrid genome consolidation. Sat, 31 Dec 2011 13:30:00 GMT http://hdl.handle.net/2440/77681 2011-12-31T13:30:00Z