Modulation of host nuclear ploidy: a common plant biotroph mechanism

Plant biotrophs often establish highly specialized and localized interaction sites where sustained nutrient exchange occurs. Increased plant nuclear DNA ploidy at or adjacent to these sites has now been reported for a diverse set of interactions, including those with fungal and bacterial symbionts and parasitic fungi and nematodes. Also, novel regulators of induced endoreduplication have recently been identified. When localized host endoreduplication is reduced, so too is the growth and/or development of the biotroph, suggesting endoreduplication supports the enhanced metabolic demands imposed by these interactions. Transcriptome analyses support this function and further identify specific ploidy-impacted processes. Remarkably, notwithstanding differences in time scales, the ploidy-impacted processes are consistent with the Gene Balance Hypothesis, which can also be used to predict effector targets. As effector influence may diminish with enhanced ploidy, these interaction sites may be uniquely suited to identify effector-impacted processes as well as elucidate endocycle regulation and function.