Insights into the multi-chromosomal mitochondrial genome structure of the xero-halophytic plant Haloxylon Ammodendron (C.A.Mey.) Bunge ex Fenzl.

BACKGROUND: Haloxylon ammodendron holds significance as an ecological plant, showcasing remarkable adaptability to desert conditions, halophytic environments, and sand fixation. With its potential for carbon sequestration, it emerges as a promising candidate for environmental sustainability. Furthermore, it serves as a valuable C4 plant model, offering insights into the genetic foundations of extreme drought tolerance. Despite the availability of plastid and nuclear genomes, the absence of a mitochondrial genome (mitogenome or mtDNA) hinders a comprehensive understanding of its its mtDNA structure, organization, and phylogenetic implications. RESULTS: In the present study, the mitochondrial genome of H. ammodendron was assembled and annotated, resulting in a multi-chromosomal configuration with two circular chromosomes. The mtDNA measured 210,149 bp in length and contained 31 protein-coding genes, 18 tRNA and three rRNA. Our analysis identified a total of 66 simple sequence repeats along with 27 tandem repeats, 312 forward repeats, and 303 palindromic repeats were found. Notably, 17 sequence fragments displayed homology between the mtDNA and chloroplast genome (cpDNA), spanning 5233 bp, accounting for 2.49% of the total mitogenome size. Additionally, we predicted 337 RNA editing sites, all of the C-to-U conversion type. Phylogenetic inference confidently placed H. ammodendron in the Amaranthacea family and its close relative, Suaeda glacum. CONCLUSIONS: H. ammodendron mtDNA showed a multi-chromosomal structure with two fully circularized molecules. This newly characterized mtDNA represents a valuable resource for gaining insights into the basis of mtDNA structure variation within Caryophyllales and the evolution of land plants, contributing to their identification, and classification.

Chromosome-level genome assembly of the endangered plant Tetraena mongolica.

Tetraena mongolica is an endangered xerophytic shrub with high ecological value for the restoration of desert vegetation because of its high tolerance to drought and heat stress. Here, we generated a high-quality chromosome-level reference genome of T. mongolica by combining PacBio HiFi data and Hi-C sequencing technologies, which was approximately 1.12 Gb (contig N50 of 25.5 Mb) in size and contained 61,888 protein-coding genes; repetitive sequences comprised 44.8% of the genome. This genome of T. mongolica is the first published genome sequence of a member of the order Zygophyllales. Genome analysis showed that T. mongolica has undergone a recent whole genome duplication event, and a recent burst of long terminal repeat insertions afterward, which may be responsible for its genome size expansion and drought adaptation. We also conducted searches for gene homologues and identified terpene synthase (TPS) gene families and candidate genes involved in triacylglycerol biosynthesis. The T. mongolica genome sequence could aid future studies aimed at functional gene identification, germplasm resource management, molecular breeding efforts, as well as evolutionary studies of Fabids and angiosperm taxa.