**5. Conclusions**

We present evidence of mitochondrial mRNA processing from two green algae from the chlorophyte and streptophyte lineages with similarly sized circular mitochondrial genomes. The primary differences were the absence of secondary structures (t-elements) in the *P. duplex* chondriome that are important for processing in streptophytes, and the removal of the 5- UTR in chlorophytes but not streptophytes. We hypothesize that telements were gained and the 5- UTR processing lost in the common ancestor of the streptophytic algae. We also confirm the polycytidylation of the 3 termini of *P. duplex* but not *C. vulgaris*, which is consistent with the theory that poly(C) addition is limited to chlorophytes.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2223-774 7/10/3/576/s1, Figure S1: Logo plots, Figure S2: Hypothetical RNA secondary structures, Table S1: DNA oligo primers.

**Author Contributions:** Conceptualization, A.B.C., K.M.M., G.C.R.P., M.J.M.; methodology, A.B.C., K.M.M., G.C.R.P., M.J.M.; investigation, G.C.R.P., M.J.M.; resources, A.B.C., K.M.M.; writing—original draft preparation, A.B.C., G.C.R.P., M.J.M.; writing—review and editing, A.B.C., K.M.M., G.C.R.P., M.J.M.; visualization, A.B.C., G.C.R.P.; supervision, A.B.C., K.M.M.; project administration, A.B.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This research was funded by the Buchanan Chair of Biology Endowment at UVA-Wise. MJM and GCRP were supported by the Fellowship in Natural Sciences program at UVA-Wise.

**Conflicts of Interest:** The authors declare no conflict of interest.
