Unraveling the Mixed Ancestry of Australasian Cress Species

Jim Crocker
11th May, 2024

Unraveling the Mixed Ancestry of Australasian Cress Species

Image Source: Natural Science News, 2024

Key Findings

  • New Zealand's Lepidium plants have complex genetic histories involving hybridization and multiple sets of chromosomes
  • The study suggests these plants may have evolved through interbreeding between species with different chromosome numbers
  • Genetic links between New Zealand Lepidium species and American relatives were identified, indicating a trans-oceanic connection in their evolution
Understanding the complex lineage of New Zealand's unique Lepidium plants has been a challenge for scientists. The country is home to 16 endemic species of this plant group, some of which are considered extinct or shared with neighboring Australia. Researchers from Manaaki Whenua − Landcare Research have conducted a study[1] that sheds light on the genetic history of these plants, revealing a story of hybridization and polyploidy—a condition where a cell has more than two paired sets of chromosomes. Previous studies have suggested that the internal transcribed spacer (ITS) region is a popular sequence for phylogenetic inference in plants[2], although its reliability has been debated due to issues like sequence variation and the presence of pseudogenes. Meanwhile, techniques such as fluorescence in situ hybridisation (FISH) and genomic in situ hybridisation (GISH) have been instrumental in studying hybridization and polyploidy in plants[3]. Furthermore, research on the mustard family, to which Lepidium belongs, has revealed discordance between nuclear and plastome data, suggesting widespread hybridization[4]. The Manaaki Whenua − Landcare Research team generated sequence data for 15 genes from various Lepidium species endemic to New Zealand, as well as from species of African, American, and Australian origin naturalized in the country. This data was analyzed alongside publicly available genomic data from other Lepidium species. The results supported the existence of two main groups of endemic New Zealand Lepidium, each with distinct dominant nrDNA sequences, and suggested differences in ploidy levels—one group being octoploid and the other having uncertain ploidy. The octoploid species appeared to combine four distinguishable subgenomes. Interestingly, the study suggests that allopolyploidisation events may have occurred between these octoploid species and a diploid species closely related to L. africanum. This process, where species with different levels of ploidy hybridize, can lead to the creation of new species with novel genetic combinations. The research also found support for previous hypotheses that linked New Zealand Lepidium to American species, with at least two Australasian Lepidium subgenomes related to those present in American polyploid species. The origins of two additional subgenomes in the Australasian Lepidium are yet to be determined, but they may also be of American origin. One particularly intriguing finding was regarding Lepidium naufragorum, an endemic New Zealand species. Its genetic sequences suggest it could be an octodecaploid, potentially arising from hybridization between octoploid and decaploid New Zealand groups. This would make it a complex example of polyploidy and hybridization. The study not only provides insights into the evolutionary history of New Zealand's Lepidium but also underscores the importance of using a combination of genetic data and modern sequencing techniques to unravel the complexities of plant phylogeny. It builds upon previous research[2][3][4] by applying targeted gene analysis to understand the role of hybridization and polyploidy in the diversification of plant species. In conclusion, the research from Manaaki Whenua − Landcare Research contributes significantly to our understanding of the genetic makeup and evolutionary processes that have shaped the unique biodiversity of New Zealand's Lepidium species. It highlights the intricate dance of genetics that occurs over millennia, leading to the rich tapestry of life we see today. This study not only clarifies the lineage of these endemic plants but also provides a framework for future research into plant evolution and conservation.

GeneticsPlant ScienceEvolution

References

Main Study

1) Revisiting the bicontinental allopolyploid origin of Australasian Lepidium species with amplicon sequencing of 15 nuclear genes

Published 10th May, 2024

https://doi.org/10.1007/s00606-024-01899-x

Related Studies

2) Ribosomal ITS sequences and plant phylogenetic inference.

Journal: Molecular phylogenetics and evolution, Issue: Vol 29, Issue 3, Dec 2003

3) Review of the Application of Modern Cytogenetic Methods (FISH/GISH) to the Study of Reticulation (Polyploidy/Hybridisation).

https://doi.org/10.3390/genes1020166

4) Global Brassicaceae phylogeny based on filtering of 1,000-gene dataset.

https://doi.org/10.1016/j.cub.2023.08.026


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