Gene functionalities and genome structure in Bathycoccus prasinos reflect cellul ar specializations at the base of the green lineage

Bathycoccu s prasinos is an extremely small cosmopolitan marine green alga whose cells are covered with intricate spider's web patte rned scales that develop within the Golgi cisternae before their transport to the cell surface. Its small genome of 15Mb i s divided over 19 chromosomes and lacks transposons. Although seventy percent of all B. prasinos genes share similarities with other Viridiplantae genes, up to 428 genes were probably acquired by horizontal gene transfer (HGT), mainly from othe r eukaryotes. Two chromosomes, one big and one small, are atypical, an unusual synapomorphic feature within the Mamiellale s. Genes on these atypical outlier chromosomes show lower GC content and a significant fraction of putative HGT genes. Whe reas the small outlier chromosome lacks colinearity with other Mamiellales and contains many unknown genes without homolog s in other species, the big outlier shows a higher intron content, increased expression levels and a unique clustering pat tern of housekeeping functionalities. Four gene families are highly expanded in B. prasinos, including sialyltransferases, sialidases, ankyrin repeats and zinc ion-binding genes, and we hypothize that these genes are associated with the process of scale biogenesis. The minimal genomes of the Mamiellales provide a baseline for evolutionary and functional analyses o f metabolic processes in green plants.

Moreau, H., Verhelst, B., Couloux, A., Derelle, E., Rombauts, S., Grimsley, N., Van Bel, M., Poulain, J., Katinka, M., Hohmann-Marriott, M., Piganeau, G., Rouzé, P., Da Silva, C., Wincker, P., Van de Peer, Y., Vandepoele, K. (2012) Gene functionalities and genome structure in Bathycoccus prasinos reflect cellular specializations at the base of the green lineage . Genome Biol. 13, R74.

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