The fatty acid synthase was lost at the origin of the Glomeromycotina lineage. All species have delta, and only the Glomeraceae family lost epsilon

In symbiosis with a host, we detect regularly-spaced nuclei pairs that appear to be mitotic. We find paired nuclei in spores germinated in vitro much less frequently. This suggests that the Glomeraceae cell cycle is active in planta, coinciding with the up-regulation of replication gene expression.

This raises the question of how these fungi can replicate DNA. We grew the model species R. irregularis in vitro for 3 weeks without a host, and detected no increase in chromosomal DNA amount – if anything, it decreases. This suggests that the cell cycle is inactive in asymbiotic spores.

The Glomeraceae family of AM fungi has an unexpectedly reduced replisome, lacking the leading strand DNA polymerase and associated co-factors.

AM fungi have therefore experienced reductive evolution beyond the loss of the fatty acid synthase.

In this study, we found that two major lineages of endosymbiotic fungi have lost DNA polymerase genes.

In AM fungi, DNA polymerase losses are lineage-specific.

Microsporidia lost the same DNA polymerases and accessory co-factors as AM fungi, but in a slightly different order.

Guess the ggplot colour palette!