Journal Articles

Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915

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    Evolutionary relationships in Santalales inferred using target capture with Angiosperms353, focusing on Australasian Santalaceae sensu lato
    (CSIRO Publishing, Australia, 2025-08) Anderson BM; Edlund M; James SA; Lepschi BJ; Nickrent DL; Sultan A; Tate JA; Petersen G; Murphy D
    The angiosperm order Santalales comprises more than 2500 species, most of which are hemi- or holoparasitic on other plants, and derive water and nutrients via specialised structures that attach to host roots or stems. The parasitic lifestyle has affected the morphology and genomes of these plants, and classification of the order has been difficult, with outstanding questions about membership of and relationships between families in the order. We chose to focus on improving phylogenetic sampling in the broadly circumscribed Santalaceae sens. lat., with emphasis on Australasian members of Amphorogynaceae and Viscaceae as part of the Genomics for Australian Plants Initiative. We used target capture with the Angiosperms353 bait set to generate a dataset of 318 nuclear loci × 195 samples, including publicly available data from other Santalales families. Phylogenetic inferences using maximum likelihood concatenation and a summary coalescent approach were largely congruent and resolved relationships between most families, agreeing with much of the previous work on the order. Some relationships that have been difficult to resolve remained so, such as branching order among some families in Olacaceae sens. lat. and Santalaceae sens. lat. Denser sampling in Amphorogynaceae and Viscaceae provided new insights into species-level relationships in genera such as Leptomeria and Choretrum, and allowed testing of recent phylogenetic work in Korthalsella. Our new phylogenetic hypothesis is consistent with one origin of root hemiparasitism, two origins of holoparasitism and five origins of aerial parasitism in the order. Although Angiosperms353 was successful, some phylogenetic bias in gene recovery suggests that future studies may benefit from more specific baits and deeper sequencing, especially for Viscaceae.
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    Polyploidy on islands - concerted evolution and gene loss amid chromosomal stasis
    (Oxford University Press on behalf of the Annals of Botany Company, 2023-01-01) Joshi P; Ansari H; Dickson R; Ellison NW; Skema C; Tate JA
    BACKGROUND AND AIMS: Polyploidy is an important process that often generates genomic diversity within lineages, but it can also cause changes that result in loss of genomic material. Island lineages, while often polyploid, typically show chromosomal stasis but have not been investigated in detail regarding smaller-scale gene loss. Our aim was to investigate post-polyploidization genome dynamics in a chromosomally stable lineage of Malvaceae endemic to New Zealand. METHODS: We determined chromosome numbers and used fluorescence in situ hybridization to localize 18S and 5S rDNA. Gene sequencing of 18S rDNA, the internal transcribed spacers (ITS) with intervening 5.8S rDNA, and a low-copy nuclear gene, GBSSI-1, was undertaken to determine if gene loss occurred in the New Zealand lineage following polyploidy. KEY RESULTS: The chromosome number for all species investigated was 2n = 42, with the first published report for the monotypic Australian genus Asterotrichion. The five species investigated all had two 5S rDNA signals localized interstitially on the long arm of one of the largest chromosome pairs. All species, except Plagianthus regius, had two 18S rDNA signals localized proximally on the short arm of one of the smallest chromosome pairs. Plagianthus regius had two additional 18S rDNA signals on a separate chromosome, giving a total of four. Sequencing of nuclear ribosomal 18S rDNA and the ITS cistron indicated loss of historical ribosomal repeats. Phylogenetic analysis of a low-copy nuclear gene, GBSSI-1, indicated that some lineages maintained three copies of the locus, while others have lost one or two copies. CONCLUSIONS: Although island endemic lineages show chromosomal stasis, with no additional changes in chromosome number, they may undergo smaller-scale processes of gene loss and concerted evolution ultimately leading to further genome restructuring and downsizing.