Distribution of haploid chromosomes into separate nuclei in two pathogenic fungi

Nuclei define eukaryotes, enabling macromolecular compartmentalization and cellular regulation. Each nucleus is believed to contain one or more haploid sets of chromosomes (1N). However, we discovered that haploid cells of the pathogenic fungi Sclerotinia sclerotiorum and Botrytis cinerea distribute their chromosomes such that each of their nuclei contains only a subset of the haploid chromosomes (≤½N). The unusual chromosomal distribution was confirmed by cellular and molecular methods including chromosome counting, fluorescence in situ hybridization, flow cytometry–based DNA measurements, and single-nucleus polymerase chain reaction experiments. This phenomenon challenges fundamental assumptions about nuclear organization and opens fresh avenues in chromosome biology.