Local endoreduplication of the host is a conserved process during Phytomyxea-host interaction

Area of Science:

• Cell Biology
• Plant Pathology
• Marine Biology

Background:

• Endoreduplication is a cell cycle modification where DNA replicates without cell division, observed across diverse organisms.
• Biotrophic pathogens often induce endoreduplication in host plants to enhance resource acquisition.

Purpose of the Study:

• To investigate endoreduplication induced by Rhizaria organisms, specifically *Maullinia spp.* in brown algae and *Plasmodiophora brassicae* in plants.
• To explore the molecular mechanisms underlying pathogen-induced endoreduplication in phylogenetically distant hosts.

Main Methods:

• Utilized fluorescent *in situ* hybridization (FISH) combined with nuclear area measurements.
• Analyzed RNA-sequencing (RNA-seq) datasets from infected host organisms.

Main Results:

• Confirmed *Plasmodiophora brassicae* induces endoreduplication in infected plants.
• First-time demonstration of pathogen-induced endoreduplication in brown algae infected by *Maullinia ectocarpii* and *Maullinia braseltonii*.
• Identified upregulated cell cycle regulators (CCS52A1/B, CCS52, WEE1) in RNA-seq data, suggesting their role in the cell cycle switch.

Conclusions:

• Pathogen-induced endoreduplication is a conserved mechanism in Phytomyxea-host interactions across diverse hosts.
• The findings expand the understanding of Phytomyxea's strategies for manipulating host cell cycles.
• Upregulation of specific cell cycle proteins points to key molecular players in the transition to the endocycle.