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The phylogenetic status of Quercus subg. Cyclobalanopsis has long been controversial and the interspecific relationships of some species are unclear. At present, chloroplast genomes have been used to solve the phylogenetic problems of subg. Quercus and Castanea in the Fagaceae, but there are few researches on solving the phylogenetic problems of Quercus subg. Cyclobalanopsis with chloroplast genome information. To reveal the chloroplasts genome characteristics and phylogenetic relationships of Quercus ningangensis, Q. oxyodon, Q. gambleana and Q. neglecta. In this study, mature leaves of the above four species of Quercus subg. Cyclobalanopsis were selected for next-generation sequencing, and the chloroplast genome structure and characteristics were analyzed, phylogeny was studied in combination with related taxa. The results were as follows: (1) The chloroplast genome sequences of Q. ningangensis, Q. oxyodon, Q. gambleana and Q. neglecta were 160 906, 160 883, 160 832, 160 784 bp, respectively. They all encoded 133 genes, including 88 protein-coding genes, 37 tRNA genes and 8 rRNA genes. (2) The codons ending in A/T were preferred by the four species of Quercus subg. Cyclobalanopsis, and the variation regions of plastid genome mainly existed in non-coding sequences. (3) According to IR boundary analysis, ycf1 pseudogene was found in four species of Quercus subg. Cyclobalanopsis and expanded in IRb/SSC regions. (4) Phylogenetic analysis showed that Fagus and Trigonobalanus were differentiated early in Fagaceae, while subg. Quercus did not form a monophyly. The results of phylogenetic tree based on chloroplast genome were consistent with the nuclear marker plasmid markers. Interspersed between Ilex group and Cerris group in subg. Quercus. (5) The Flora of China and some local flora treated Q. gambleana as a separate species, while ZHOU Zhekun and DENG Min et al. treated Q. gambleana as a subspecies according to the characteristics of leaves. The phylogenetic status of Q. gambleana is still controversial. Based on the chloroplast genome information and previous morphological analysis results, the present study supported the idea that Q. gambleana existed as an independent species. This study provides basic data for discussing the phylogenetic status of the Quercus subg. Cyclobalanopsis, the division of its groups, and the resolution of doubtful relationships among them. |
