Ultrastructure and phylogeny of Parietochloris toyamaensis sp. nov. and P. bilobata (Trebouxiophyceae)

Abstract

We describe Parietochloris toyamaensis sp. nov. and verify the taxonomic status of P. bilobata (originally described as Neochloris and once combined with Ettlia), using ultrastructural and molecular analyses. P. toyamaensis was isolated from soil collected in Toyama, Japan. It had a parietal chloroplast with pyrenoids that were discontinuously covered with starch segments and penetrated more or less in parallel by thylakoid membranes, and reproduced by forming naked, somewhat dorsoventral, biflagellate zoospores. Two contractile vacuoles were in line lengthwise, located in the median ventral side of the zoospores, as in the type P. alveolaris. The basal apparatus components included a single microtubule in the dexter root. P. toyamaensis was separately resolved from other members of the genus in the 18S rDNA and ITS2 trees. Since the authentic strain ASIB V141 of P. bilobata (stored as Ettlia) has been lost, ASIB V143 was used as a reference in place of it. P. bilobata ASIB V143 was resolved in the ‘Parietochloris sensu stricto’ clade but not ‘Lobosphaera’ clade in the 18S rDNA tree, so taxonomically the combination of N. bilobata with Parietochloris as P. bilobata by Andreyeva was confirmed. In zoospores of the strains of P. bilobata, contractile vacuoles were located in the ventral side, as in P. alveolaris. The taxonomic relationship between P. bilobata and P. grandis, and evaluation of the unique position of contractile vacuoles in dorsoventral zoospores as one of the key characters of Parietochloris were discussed.

Highlights

• Characterization of the species of Parietochloris by using ultrastructural and molecular data.

• Proposal of Parietochloris toyamaensis sp. nov.

• Verification of phylogenetic position of Parietochloris bilobata.

KEYWORDS:

• contractile vacuoles
• dorsoventral zoospores
• Ettlia
• 18S rDNA
• ITS2
• Neochloris
• soil algae
• microtubular roots
• Chlorophytes
• SSU rDNA

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2022.2042603

Supplementary fig. S1. Predicted secondary structure of ITS2 transcript of Parietochloris toyamaensis sp. nov. NIES-3574 (LC639356). U-U’ mismatch in Helix II and conservative motif at 5’ side in Helix III are marked by round rectangles.

Supplementary fig. S2. Predicted secondary structure of ITS2 transcript of Parietochloris alveolaris UTEX 836 (LC639355).

Supplementary fig. S3. Predicted secondary structure of ITS2 transcript of Parietochloris bilobata ASIB V143 (LC639357).

Supplementary fig. S4. Predicted secondary structure of ITS2 transcript of Parietochloris bilobata ASIB T58 (LC639358).

Supplementary fig. S5. Predicted secondary structure of ITS2 transcript of ‘Ettlia’ pseudoalveolaris (MT735204).

Author contributions

S. Watanabe: original concept, drafting and editing manuscript, analysis of molecular data, electron microscopy; N. Mezaki: analysis of molecular data, light and electron microscopy; T. Nakada: light microscopy.