In 2019 Imperial masters student Xueni (Linka) Bian conducted a thesis project to assemble, annotate and analyse the chloroplast and mitochondrial genomes of Corallina officinalis.
I assembled both the mitochondrial and plastid genomes of four latitudinally widespread populations of Corallina officinalis. I sought intraspecific variation patterns across the two sets of four closely-related genomes, which can be interpreted as signals for population-specific acclimation. Mitogenome and plastome comparisons showed that NE Atlantic populations of C. officinalis are genetically similar at the primary sequence level. A rough estimate for relative organellar proportions in populations suggested that the copy-number ratios between organellar genomes is variable between populations. Further investigation revealed that the mitogenome origin of replication coincides with a ~200bp stem-loop motif in the large intergenic region that is intraspecifically highly variable. Few studies have investigated both mitochondria and plastids in parallel, and this study is one of the first to multiply-sample the same red-algal species for both of its organellar genomes. Two patterns generally observed in organellar evolution are extended down to the intraspecific level for C. officinalis: (1) mitogenomes are more variable than plastomes in primary sequence and (2) mitogenomes show evidence for structural embellishment at their replication origin, which may allow conspecific populations to achieve “nuanced” copy number control, despite nuclear-enforced conservatism in mitochondrial-encoded genes.
Bian X (2019) Nuance and Numerosity: Organellar genomes reveal intraspecific variation between four populations of Corallina officinalis (Corallinales, Rhodophyta). Thesis project for the MRes in Biosystematics at University College London. Supervised by Dr Chris Yesson & Prof Juliet Brodie. (pdf)