Chloroplast Genome and Description of <i>Borodinellopsis insignis</i> sp. nov. (Chlamydomonadales, Chlorophyta), a Rare Aerial Alga from China

Abstract

The genus Borodinellopsis is extremely rare and is the subject of limited research and reports. It currently comprises only two species, Borodinellopsis texensis and Borodinellopsis oleifera, which differ from other globose algae due to their unique centrally radiating chloroplasts. In this study, we describe a new specimen in detail based on morphological data and phylogenetic analysis and identify it as B. insignis. B. insignis and B. texensis exhibit a high degree of similarity, likely due to their shared characteristics of centrally radiating chloroplasts and flagella that are significantly longer than the cell body. A phylogenetic tree constructed based on the 18S rDNA sequence indicates that B. insignis and B. texensis form a branch that is distinct from other genera, such as Tetracystis, Spongiococcum, and Chlorococcum. Phylogenetic analysis of the ITS sequence, the rbcL gene, and the tufA gene reveals that B. insignis is significantly different from B. texensis, in that it has oil droplets, smaller vegetative cells and zoospores, and distinct habitats. It is also different from B.oleifera as it has smaller vegetative cells and zoospores, turns red after cultivation, has longer flagella, and resides in different habitats. The chloroplast genomes of B. texensis and B. insignis further show significant differences, with the phylogenetic tree constructed based on the analysis of 49 protein-coding genes forming two separate branches. The collinearity of the chloroplast genomes in B. texensis and B. insignis is poor, with 15 out of the 31 homologous modules displaying inversions and complex rearrangements. Given these differences, we classify this alga as a new species and named it Borodinellopsis insignis sp. nov.

Keywords

• <i>Borodinellopsis</i>
• new species
• phylogenetic analysis
• 18S rDNA
• chloroplast genome
• Chlorococcaceae