Background: Acer truncatum (purpleblow maple) is a woody tree species that produces seeds with high levels of valuable fatty acids (especially nervonic acid). The species is admired as a landscape plant with high developmental prospects and scientific research value. The A. truncatum chloroplast genome has recently been reported; however, the mitochondrial genome (mitogenome) is still unexplored. Results: We characterized the A. truncatum mitogenome, which was assembled using reads from PacBio and Illumina sequencing platforms, performed a comparative analysis against different species of Acer. The circular mitogenome of A. truncatum has a length of 791,052 bp, with a base composition of 27.11% A, 27.21% T, 22.79% G, and 22.89% C. The A. truncatum mitogenome contains 62 genes, including 35 protein-coding genes, 23 tRNA genes and 4 rRNA genes. We also examined codon usage, sequence repeats, RNA editing and selective pressure in the A. truncatum mitogenome. To determine the evolutionary and taxonomic status of A. truncatum, we conducted a phylogenetic analysis based on the mitogenomes of A. truncatum and 25 other taxa. In addition, the gene migration from chloroplast and nuclear genomes to the mitogenome were analyzed. Finally, we developed a novel NAD1 intron indel marker for distinguishing several Acer species. Conclusions: In this study, we assembled and annotated the mitogenome of A. truncatum, a woody oil-tree species producing nervonic acid. The results of our analyses provide comprehensive information on the A. truncatum mitogenome, which would facilitate evolutionary research and molecular barcoding in Acer.

Acer truncatum, which is a new woody oil tree species, is an important ornamental and medicinal plant in China. To assess the genetic diversity and relationships of A. truncatum, we analyzed its complete chloroplast (cp) genome sequence. The A. truncatum cp genome comprises 156,492 bp, with the large single-copy, small single-copy, and inverted repeat (IR) regions consisting of 86,010, 18,050, and 26,216 bp, respectively. The A. truncatum cp genome contains 112 unique functional genes (i.e., 4 rRNA, 30 tRNA, and 78 protein-coding genes) as well as 78 simple sequence repeats, 9 forward repeats, 1 reverse repeat, 5 palindromic repeats, and 7 tandem repeats. We analyzed the expansion/contraction of the IR regions in the cp genomes of six Acer species. A comparison of these cp genomes indicated the noncoding regions were more diverse than the coding regions. A phylogenetic analysis revealed that A. truncatum is closely related to A. miaotaiense. Moreover, a novel ycf4-cemA indel marker was developed for distinguishing several Acer species (i.e., A. buergerianum, A. truncatum, A. henryi, A. negundo, A. ginnala, and A. tonkinense). The results of the current study provide valuable information for future evolutionary studies and the molecular barcoding of Acer species.

The plant mitochondrial genome (mitogenome) has a complex organization and carries genetic traits of value in exploiting genetic resources. In this study, the Ilex macrocarpa mitogenome was sequenced and assembled to understand the genetic diversity and phylogenetic relationship. The mitogenome has a cyclic molecular structure and is 539,461 bp long with a GC content of 45.53%. It contained 39 protein-coding proteins, 19 tRNA genes, and 3 rRNA genes. The 146 simple sequence repeats and 591 dispersed repeat sequences were identified in the mitogenome. Codon usage analysis revealed a preference for codons ending in A/T. A total of 517 C to U RNA editing sites were predicted, with nad4 and ccmB being edited most frequently (39 times). Phylogenetic analysis via mitochondrial protein-coding genes showed that the Aquifoliales order contains sister plants to Lamiales, Solanales, and Gentianales. In addition, the conflicts between chloroplast and mitochondrial phylogeny were also observed. This study provides a theoretical framework for understanding the evolution, classification, and identification of the Ilex genus, which lays an important foundation for future molecular breeding investigations.

Background: Water uptake is essential for seed germination. However, Gleditsia sinensis seeds have a water-impermeable seed coat, which is beneficial for its adaption to the environment, but prohibits its germination without treatment. This feature may be associated with the structure of the seed coat. Thus, the aim of this research was to identify and describe the initial water uptake site and water movement and to determine the relationship between seed coat structure and water absorption. Results: A water temperature of 80 °C was optimal to break the hardseededness of G. sinensis seeds. Scanning electron microscopy (SEM) images revealed that the seed coat consisted of a palisade layer and light line that can hinder water entry into the seed. Also, a structure of vascular bundles existed in the hilar region. Hot water treatment caused the tightly closed micropyle to open and the cavity beneath it expanded; the layer of palisade cells in the lens was raised. The embryo dye-tracking tests showed that the radicle tip was the initial region to be stained red. After staining for 24 h, the red-stained area on the vascular bundle side of cotyledon was more extensive than that on the other side. Further studies by MRI maps indicated that the micropyle was the initial site for water imbibition. Some water then migrated along the space between the seed coat and the endosperm to the chalazal; simultaneously, the rest of the water reached the embryonic axis and spread into cotyledons. The maps of 20–24 h showed that water was unevenly distributed within the cotyledons in a way that the edge parts were more hydrated than the center. Blocking tests showed that the hilar region was the initial and an important region during seed imbibition. The medial region and chalazal portion were capable of imbibing water when the hilar region was blocked, but water absorption was later and slower than that through the hilar region. Conclusion: MRI technology provides a promising and non-invasive technique to identify the water gap and the path of water movement in the seed. Combined with the results of SEM, the relation between seed coat and its imbibition can be inferred.