Nuclear organization in crucifer genomes: nucleolus-associated telomere clustering is not universal interphase configuration in Brassicaceae

Shan W, Kubová M, Mandáková T, Lysak MA

Plant Journal: doi: 10.1111/tpj.15459.

Abstract

Arabidopsis thaliana (arabidopsis) has become a major plant research model where interphase nuclear organization exhibits unique features, including nucleolus-associated telomere clustering. The chromocenter (CC)-loop model, or rosette-like configuration, describes intranuclear chromatin organization in arabidopsis as megabase-long loops anchored in, and emanating from, peripherally positioned chromocenters, and those containing telomeres associate with the nucleolus. To investigate whether the CC-loop organization is universal across the mustard family (crucifers), the nuclear distributions of centromeres, telomeres and nucleoli were analyzed by fluorescence in situ hybridization in seven diploid species (2n = 10 - 16) representing major crucifer clades with an up to 26-fold variation in genome size (160 Mb – 4 260 Mb). Nucleolus-associated telomere clustering was confirmed in arabidopsis (157 Mb) and was newly identified as the major nuclear phenotype in other species with a small genome (215 – 381 Mb). In large-genome species (2 611 – 4 264 Mb), centromeres and telomeres adopted either a Rabl-like configuration or dispersed distribution in the nuclear interior; telomeres only rarely associated with the nucleolus. In Arabis cypria (381 Mb) and Bunias orientalis (2 611 Mb), tissue-specific patterns deviating from the major nuclear phenotypes were observed in anther and stem tissues, respectively. The rosette-like configuration, including nucleolus-associated telomere clustering in small-genome species from different infrafamiliar clades, suggests that genomic properties rather than phylogenetic position, determine the interphase nuclear organization. Our data suggest that nuclear genome size, average chromosome size and degree of longitudinal chromosome compartmentalization affect interphase chromosome organization in crucifer genomes.

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