Primulina hunanensis K. M. Liu & X. Z. Cai is a perennial herb in the genus Primulina Hance of the family Gesneriaceae. It is very adaptable to low light and barren cave environments, and is unique in its species evolution and adaptation to the environment. P. hunanensis has beautiful flowers and a graceful shape, which makes it valuable for horticultural cultivation. However, its habitat is special and its distribution range is extremely narrow, and it is only found in one county in Hunan Province. The wild population is estimated to be less than 800 plants, and it is classified as an endangered plant, representing a very small population of wild plants in Hunan.

Mitochondrial genome (mtDNA) research has also been applied to planting preservation and genetic improvement. In Gesneriaceae, mtDNA of only two species have been reported.

Recently, the East African Flora and Taxonomy Group of Wuhan Botanical Garden, in collaboration with the Plant Taxonomy Team of the College of Life Sciences, Hunan Normal University, completed the sequencing and assembly of the complete mtDNA of P. hunanensis for the first time by using the latest sequencing technology with the advantage of long-reads (Nanopore). The study analyzed the mtDNA features of P. hunanensis, including gene content, codon usage preference, repetitive sequences, RNA editing, and comparative phylogenetic relationships and genome covariance with the published mtDNA in Labiatae.

The results of the study showed that: the mtDNA of P. hunanensis was 575,242 bp in total length, with a GC content of 43.54%. Long-reads data supported the assembly into a linear structure encoding a total of 60 genes, including 37 protein-coding genes, 20 Transfer RNA genes, and 3 Ribosome RNA genes. Protein-coding genes accounted for 9.32% of the total length of the mtDNA , and a total of 31 codons had relative synonymous codon usage values greater than 1.116 simple repeats, seven tandem repeats, and 362 dispersed repeat sequences were detected, and 455 potential RNA editing sites were identified. The covariance results indicated a large number of genomic rearrangements between P. hunanensis and closely related species. The topology of the mitochondrial genome-based phylogeny showed that P. hunanensis was closely related to Boea hygrometrica.

This is the first complete mtDNA within Primulina and the third complete mtDNA within Gesneriaceae to be reported, which is an important addition to the limited mtDNA database of plants.

The research results were published in the international botanical journal BMC Genomics under the title of “Assembly and comparative analysis of the initial complete mitochondrial genome ofPrimulina hunanensis(Gesneriaceae): a cave-dwelling endangered plant”. CHEN Lingling, a master’s student jointly trained by Wuhan Botanical Garden and Hunan Normal University, and Dr. DONG Xiang from Wuhan Botanical Garden are the co-authors, while Associate Professor CAI Xiuzhen from Hunan Normal University and Professor HU Guangwan from Wuhan Botanical Garden are the co-corresponding authors.

The research was supported by the National Wild Plant Germplasm Resource Center and funded by the National Science & Technology Fundamental Resources Investigation Program of China, the National Natural Science Foundation of China, the Project of National Plant Specimen Resource Center, and the Open Fund of Key Laboratory of Orchid Plant Protection and Utilization, National Forestry and Grassland Administration.

MtDNA map of P. hunanensis (Image by WBG)

The phylogenetic associations of P. hunanensis alongside 32 other plant species. Phylogenetic tree constructed by maximum likelihood method based on 26 conserved mitochondrial genomic PCGs (Image by WBG)