Here, we present new transcriptome sequencing data from seven species of Dasycladales (Ulvophyceae) and a phylogenomic analysis of the Chlorophyta with a particular focus on Ulvophyceae. We have focused on a broad selection of green algal groups and carefully selected genes suitable for reconstructing deep eukaryote evolutionary histories. Increasing the taxon sampling of Dasycladales restructures the Ulvophyceae by identifying Dasycladales as closely related to Scotinosphaerales and Oltmannsiellopsidales. Contrary to previous studies, we do not find support for a close relationship between Dasycladales and a group with Cladophorales and Trentepohliales. Instead, the latter group is sister to the remainder of the Ulvophyceae. Furthermore, our analyses show high and consistent statistical support for a sister relationship between Bryopsidales and Chlorophyceae in trees generated with both homogeneous and heterogeneous (heterotachy) evolutionary models. Our study provides a new framework for interpreting the evolutionary history of Ulvophyceae and the evolution of cellular morphologies.

No abstract

The macroscopic single-celled green alga Acetabularia acetabulum has been a model system in cell biology for more than a century. However, no genomic information is available from this species. Since the alga has a long life cycle, is difficult to grow in dense cultures, and has an estimated diploid genome size of almost 2 Gb, obtaining sufficient genomic material for genome sequencing is challenging. Here, we have attempted to overcome these challenges by amplifying genomic DNA using multiple displacement amplification (MDA) combined with microfluidics technology to distribute the amplification reactions across thousands of microscopic droplets. By amplifying and sequencing DNA from five single cells we were able to recover an estimated ~ 7–11% of the total genome, providing the first draft of the A. acetabulum genome. We highlight challenges associated with genome recovery and assembly of MDA data due to biases arising during genome amplification, and hope that our study can serve as a reference for future attempts on sequencing the genome from non-model eukaryotes.

Acetabularia acetabulum is a single-celled green alga previously used as a model species for studying the role of the nucleus in cell development and morphogenesis. The highly elongated cell, which stretches several centimeters, harbors a single nucleus located in the basal end. Although A. acetabulum historically has been an important model in cell biology, almost nothing is known about its gene content, or how gene products are distributed in the cell. To study the composition and distribution of mRNAs in A. acetabulum, we have used quantitative RNA-seq to sequence the mRNA content of four sections of adult A. acetabulum cells. We found that although mRNAs are present throughout the cell, there are large pools of distinct mRNAs localized to the different subcellular sections. Conversely, we also find that gene transcripts related to intracellular transport are evenly distributed throughout the cell. This distribution hints at post-transcriptional regulation and selective transport of mRNAs as mechanisms to achieve mRNA localization in A. acetabulum.