Decoding Evolution of Rubioideae: Plastomes Reveal Sweet Secrets of Codon Usage, Diagnostides, and Superbarcoding.

Galium genus belongs to the Rubiaceae family, which consists of approximately 14,000 species. In comparison to its well-known relatives, the plastomes of the Galium genus have not been explored so far. The plastomes of this genus have a typical, quadripartite structure, but differ in gene content, since the infA gene is missing in Galium palustre and Galium trfidum. An evaluation of the effectiveness of using entire chloroplast genome sequences as superbarcodes for accurate plant species identification revealed the high potential of this method for molecular delimitation within the genus and tribe. The trnE-UUC-psbD region showed the biggest number of diagnostides (diagnostic nucleotides) which might be new potential barcodes, not only in Galium, but also in other closely related genera. Relative synonymous codon usage (RSCU) appeared to be connected with the phylogeny of the Rubiaceae family, showing that during evolution, plants started preferring specific codons over others.

Nanopore sequencing of chloroplast genome of Scapania undulata (L.) Dumort., 1835 (Scapaniaceae, Jungermanniales).

We performed long-read sequencing of the Scapania undulata (L.) Dumort. chloroplast genome with Oxford Nanopore Technology using improved flow cells (10.3). S. undulata is a leafy liverwort living on rocks in or near water in mountains. The size of the complete plastome sequence is 117,651 bp long, the large single copy (LSC) region is 80,606 bp long, the small single copy (SSC) region is 19,401 bp long. The nanopore sequencing allowed for the distinction of inverted repeats A and B (IRA, IRB) which were not identical. Guanine cytosine (GC) ratio is 33.7% for the complete chloroplast genome, for LSC and SSC are 31.7% and 30.6%. The phylogeny reconstruction shows that Scapania undulata is the sister to S. ciliata and S. griffithii.