Comparative Analysis of the Characteristics, Phylogenetic Relationships of the Complete Chloroplast Genome, and Maternal Origin Track of White Poplar Interspecific Hybrid GM107

Abstract

White poplars are a dominant tree species in natural ecosystems throughout China, where they are also widely planted for agroforestry and industrial uses. However, the phylogenetic relationships among poplars in section Populus have a complex genetic background influenced by frequent hybridization events and, to date, only a few studies have attempted to clarify this background. In this study, we performed de novo assembly of the whole chloroplast (cp) genome of an elite individual GM107 with the size of 156,493 bp, which consists of a large single-copy (LSR) (84,610 bp), a small single-copy (SSC) (16,567 bp), and a pair of inverted repeats (27,658 bp). It comprises 127 genes, including 85 protein-coding genes, 36 tRNAs, and 6 rRNAs. Comparative analysis of the cp genomes was conducted among 7 poplars in section Populus and 4 cp DNA markers with >1% variable sites were detected. We found that Populus alba was the most closely related species to GM107 by phylogenetic analyses. RNA sequencing detected 66 genes that participated in translation, transcription, and photosynthesis. The expression levels of almost all 66 genes were higher in leaves than in other tissues, except for PtatpF and PtatpH. In all tissues, we detected higher transcript abundances of PtndhF, PtpsbA, PtpsbB, Ptrps14, PtatpF, and PtatpH than of other genes. Both cp genome and transcriptome data help understand evolution events in section Populus and unravel the origin of Chinese white poplars, and may contribute to the molecular genetic improvement of wood properties and carbon sink capacities in the breeding of poplars in this section.