Pathways to ploidy

I caught up with Andrea Genre to talk about the research behind the latest image to appear on the cover of New Phytologist (volume 223, issue 1).

Medicago truncatula root colonisation by the arbuscular mycorrhizal fungus Gigaspora margarita (outlined by the white dashes) induces a local increase in the host tissue ploidy. Coloured dots tag nuclei with putative ploidy levels ranging between 2C‐4C (red) to 128C‐256C (yellow). Courtesy of Gennaro Carotenuto.

MW: What does the image show?

AG: The image shows a map of putative ploidy in Medicago truncatula root tissues colonised by the arbuscular mycorrhizal fungus Gigaspora margarita (outlined by the white dashes). Coloured dots tag nuclei with increasing ploidy levels from red (2C-4C) to yellow (128C-256C).

In other words, the image shows a longitudinal section of a M. truncatula root, colonised by the symbiotic fungus Gigaspora margarita (white dashes). Fungal accommodation associates with ploidy increase in the host cell, from 2C-4C (red tags) to 128C-256C (yellow).

How did you capture the image?

The image is a projection of several optical sections obtained through confocal microscopy. The root section was stained with DAPI, a DNA-specific dye that marks nuclei. Nuclear size was then measured through image analysis techniques. Finally, all plant nuclei were categorized based on their size, an indirect indicator of ploidy (i.e. DNA content), and tagged with coloured dots ranging from red to yellow.

What was the aim of your research?

We aimed to understand where exactly plant cell ploidy increases (which had previously been proposed to occur in arbuscular mycorrhizas) take place. Our results show that endoreduplication leading to ploidy increases is triggered in cortical cells that prepare to host the fungus and should therefore be considered as part of the so-called prepenetration response.

How does the image contribute to the results in your paper?

This image shows that both colonised cells and their neighbours (to be colonised in the following hours) contain polyploid nuclei, indicating that ploidy increase takes place in the vicinity of intraradical fungal structures and in advance of fungal accommodation by the host cells.

Read the paper: Carotenuto, G., Volpe, V., Russo, G., Politi, M., Sciascia, I., Almeida‐Engler, J. and Genre, A. (2019) Local endoreduplication as a feature of intracellular fungal accommodation in arbuscular mycorrhizas. New Phytologist 223: 430-446. doi: 10.1111/nph.15763

Mike Whitfield
Development Coordinator
New Phytologist Trust

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