Browsing by Author "Symonds VV"

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    Cytonuclear Coordination Is Not Immediate upon Allopolyploid Formation in Tragopogon miscellus (Asteraceae) Allopolyploids.
    (2015) Sehrish T; Symonds VV; Soltis DE; Soltis PS; Tate JA
    Allopolyploids, formed by hybridization and chromosome doubling, face the immediate challenge of having duplicated nuclear genomes that interact with the haploid and maternally inherited cytoplasmic (plastid and mitochondrial) genomes. Most of our knowledge of the genomic consequences of allopolyploidy has focused on the fate of the duplicated nuclear genes without regard to their potential interactions with cytoplasmic genomes. As a step toward understanding the fates of nuclear-encoded subunits that are plastid-targeted, here we examine the retention and expression of the gene encoding the small subunit of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco; rbcS) in multiple populations of allotetraploid Tragopogon miscellus (Asteraceae). These polyploids formed recently (~80 years ago) and repeatedly from T. dubius and T. pratensis in the northwestern United States. Examination of 79 T. miscellus individuals from 10 natural populations, as well as 25 synthetic allotetraploids, including reciprocally formed plants, revealed a low percentage of naturally occurring individuals that show a bias in either gene (homeolog) loss (12%) or expression (16%), usually toward maintaining the maternal nuclear copy of rbcS. For individuals showing loss, seven retained the maternally derived rbcS homeolog only, while three had the paternally derived copy. All of the synthetic polyploid individuals examined (S0 and S1 generations) retained and expressed both parental homeologs. These results demonstrate that cytonuclear coordination does not happen immediately upon polyploid formation in Tragopogon miscellus.
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    Mapping QTL associated with resistance to Pseudomonas syringae pv. actinidiae in kiwifruit (Actinidia chinensis var. chinensis).
    (Frontiers Media S.A., 2024-03-26) Flay C; Symonds VV; Storey R; Davy M; Datson P; Hinrichsen P
    Pseudomonas syringae pv. actinidiae (Psa) is a bacterial pathogen of kiwifruit. This pathogen causes leaf-spotting, cane dieback, wilting, cankers (lesions), and in severe cases, plant death. Families of diploid A. chinensis seedlings grown in the field show a range of susceptibilities to the disease with up to 100% of seedlings in some families succumbing to Psa. But the effect of selection for field resistance to Psa on the alleles that remain in surviving seedlings has not been assessed. The objective of this work was to analyse, the effect of plant removal from Psa on the allele frequency of an incomplete-factorial-cross population. This population was founded using a range of genotypically distinct diploid A. chinensis var. chinensis parents to make 28 F1 families. However, because of the diversity of these families, low numbers of surviving individuals, and a lack of samples from dead individuals, standard QTL mapping approaches were unlikely to yield good results. Instead, a modified bulk segregant analysis (BSA) overcame these drawbacks while reducing the costs of sampling and sample processing, and the complexity of data analysis. Because the method was modified, part one of this work was used to determine the signal strength required for a QTL to be detected with BSA. Once QTL detection accuracy was known, part two of this work analysed the 28 families from the incomplete-factorial-cross population that had multiple individuals removed due to Psa infection. Each family was assigned to one of eight bulks based on a single parent that contributed to the families. DNA was extracted in bulk by grinding sampled leaf discs together before DNA extraction. Each sample bulk was compared against a bulk made up of WGS data from the parents contributing to the sample bulk. The deviation in allele frequency from the expected allele frequency within surviving populations using the modified BSA method was able to identify 11 QTLs for Psa that were present in at least two analyses. The identification of these Psa resistance QTL will enable marker development to selectively breed for resistance to Psa in future kiwifruit breeding programs.
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    Taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis; Boraginaceae) based on morphological, population genetic and climate-edaphic niche modelling data
    (CSIRO Publishing, 2022-05-05) Prebble JM; Symonds VV; Tate JA; Meudt HM; Wilson P
    A taxonomic revision of the southern hemisphere pygmy forget-me-not group (Myosotis L.; Boraginaceae) is presented here. Climate-edaphic niches are modelled and compared for five species in the pygmy group, namely, M. antarctica Hook.f., M. brevis de Lange & Barkla, M. drucei (L.B.Moore) de Lange & Barkla, M. pygmaea Colenso and M. glauca (G.Simpson & J.S.Thomson) de Lange & Barkla, and one unnamed putative taxon, M. "Volcanic Plateau". In this case, niche-modelling data mostly do not aid species delimitation, but morphological and genetic data provide evidence for recognising the following three species within the group: M. brevis and M. glauca (both endemic to New Zealand), and an enlarged M. antarctica (native to New Zealand, Campbell Island and Chile). Myosotis antarctica is here circumscribed to include M. antarctica sens. strict., M. drucei and M. pygmaea. The following two allopatric subspecies of M. antarctica are recognised on the basis of minor morphological differences: subsp. antarctica (formerly M. antarctica from Campbell Island and Chile, M. drucei and M. "Volcanic Plateau") and subsp. traillii Kirk (formerly known by New Zealand botanists as M. pygmaea Colenso, an illegitimate name). For all three species, which are considered Threatened or At Risk, most of their genetic variation is partitioned between rather than within populations, meaning that conserving as many populations as possible should be the priority to minimise risk of extinction.