Genetic and spatial organization of the unusual chromosomes of the dinoflagellate Symbiodinium microadriaticum

Abstract

Dinoflagellates are main primary producers in the oceans, the cause of algal blooms and endosymbionts of marine invertebrates. Much remains to be understood about their biology, including their peculiar crystalline chromosomes. We assembled 94 chromosome-scale scaffolds of the genome of the coral endosymbiont Symbiodinium microadriaticum and analyzed their organization. Genes are enriched towards the ends of chromosomes and are arranged in alternating unidirectional blocks. Some chromosomes are enriched for genes involved in specific biological processes. The chromosomes fold as linear rods and each is composed of a series of structural domains separated by boundaries. Domain boundaries are positioned at sites where transcription of two gene blocks converges and disappear when cells are treated with chemicals that block transcription, indicating correlations between gene orientation, transcription and chromosome folding. The description of the genetic and spatial organization of the S. microadriaticum genome provides a foundation for deeper exploration of the extraordinary biology of dinoflagellates and their chromosomes.

The tropical coral Pocillopora acuta displays an unusual chromatin structure and shows histone H3 clipping plasticity upon bleaching

“…We did not observe any signal in the Symbiodiniaceae extract, which confirms that the low molecular weight band (12 kDa ∆H3) we observe in healthy and bleached coral truly comes from Pocillopora and not from its Symbionts. It was thought for some time that Symbiodiniace did not possess real histones ( Rizzo, 2003 ), but recent work demonstrated that they do have core histones, but usually of larger size and serving other functions than DNA packing and chromatin structure ( Bayer et al , 2012 ; Marinov & Lynch, 2015 ; Nand et al , 2021 ; Roy & Morse, 2012 ). As we suspected, their protein structure is too different to be detected on Western blots by our commercial antibodies.…”

Consensus Guidelines for Advancing Coral Holobiont Genome and Specimen Voucher Deposition

“…highly divergent (LaJeunesse et al, 2005;Lin, 2011;Aranda et al, 2016;González-Pech et al, 2019, 2021Nand et al, 2021; Supplementary Table 4). Initially, all Symbiodiniaceae were thought to comprise a single species (Freudenthal, 1962;Kevin et al, 1969;Taylor, 1974), but the accumulation of molecular data has led to our current understanding that there are likely hundreds of species spread across tens of genera within this microalgal family (LaJeunesse et al, 2018).…”

Stretching of a fractal polymer around a disc reveals KPZ-like statistics

“…As a model, it is prototypical for several biological contexts. As just one example, we mention the recently documented (via imaging [2,3] and Hi-C experiments [4]) chromosomes morphology in a certain algae (dinoflagelletes) that form cylindrical rods with helically twisted bundles of wrapped DNA. In addition, the model turns out to have surprisingly rich connections with several other fields of theoretical physics, first and foremost with KPZ statistics.…”