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Mitochondria carry the remnant of an ancestral bacterial chromosome and express those genes with a system separate and distinct from the nucleus. Mitochondrial genes are transcribed as poly-cistronic primary transcripts which are post-transcriptionally processed to create individual translationally competent mRNAs. Algae post-transcriptional processing has only been explored in Chlamydomonas reinhardtii (Class: Chlorophyceae) and the mature mRNAs are different than higher plants, having no 5′ UnTranslated Regions (UTRs), much shorter and more variable 3′ UTRs and polycytidylated mature mRNAs. In this study, we analyzed transcript termini using circular RT-PCR and PacBio Iso-Seq to survey the 3′ and 5′ UTRs and termini for two green algae, Pediastrum duplex (Class: Chlorophyceae) and Chara vulgaris (Class: Charophyceae). This enabled the comparison of processing in the chlorophyte and charophyte clades of green algae to determine if the differences in mitochondrial mRNA processing pre-date the invasion of land by embryophytes. We report that the 5′ mRNA termini and non-template 3′ termini additions in P. duplex resemble those of C. reinhardtii, suggesting a conservation of mRNA processing among the chlorophyceae. We also report that C. vulgaris mRNA UTRs are much longer than chlorophytic examples, lack polycytidylation, and are polyadenylated similar to embryophytes. This demonstrates that some mitochondrial mRNA processing events diverged with the split between chlorophytic and streptophytic algae. 

Filamentous representatives of Cladophorales (Chlorophyta) are major contributors to algal biomass of littoral communities. In the present study, community analysis of a reported bloom in the Ogeechee River in Georgia provided an opportunity to combine morphological and genetic analyses with ecological information related to an understudied nuisance alga. A polyphasic approach of incorporating genotypic and phenotypic methods led to the identification of the algal community as Pithophora roettleri (Roth) Wittrock. Morphological analysis showed a monospecific community based on the average length and diameter of the heterosporous intercalary and terminal akinetes, along with the diameter of the principal filaments. Single-gene and concatenated-gene phylogenetic analyses of the LSU (28S rRNA) and SSU (18S rRNA) markers further confirmed this species identification. In this study, we conducted a morphological treatment of P. roettleri, produced 17 novel gene sequences, and produced a new, schematic diagram illustrating the four steps of the asexual reproduction of an intercalary akinete. Morphological characteristics, like the position and shape of akinetes documented here, and the availability of genetic sequences can improve identification and further ecological understanding of filamentous green algae. Flowing mats of P. roettleri, like those observed in this study, can lower light availability for other biota and structurally alter the habitat.