Jie Shen

The size of the mitogenome varies greatly in angiosperms from different species, but the causes of expansion remain unclear. Species from the Zingiberaceae family often carry exceptionally large mitogenomes, where this phenomenon can be readily studied. C. kwangsiensis is a medicinal plant that is native to Guangxi, China, and it is traditionally used to treat blood stasis and gynecological conditions. We assembled its complete mitogenome by using the Illumina and Nanopore reads obtained from its analysis. The genome comprises 12 circular contigs with a multi-branched structure, totaling 7.76 Mb. It contains 39 protein-coding genes, 30 tRNAs (transfer RNAs), three rRNAs (ribosomal RNAs), and 652 C-to-U RNA edited sites. Repeated analysis revealed that the dispersed repeats are the major contributors to genome expansion. Comparisons with two other Zingiberaceae mitogenomes suggested that the large genome arose in a common ancestor rather than from a whole-genome duplication, with little contribution from DNA transfers from the chloroplasts and nuclei. Thus, the exceptionally large mitogenome of Curcuma appears to result largely from repeated accumulation in the non-coding regions, such as nuclear genome expansion in angiosperms. This finding also highlights the conservation of core mitochondrial genes. Our work provides new insights into mitogenomic size variations and gene conservation in plant species, including Zingiberaceae.

Taxillus chinensis (DC.) Danser is an important hemiparasitic medicinal plant whose propagation is severely limited by the desiccation sensitivity of its recalcitrant seeds. Dehydrins (DHNs), which protect plants against dehydration-induced stresses such as salinity, drought, and low temperatures, may play a critical role in protecting recalcitrant seeds. However, the role of DHNs in the seeds of T. chinensis remains unclear. In this study, a differentially expressed gene was identified from the seed transcriptome of T. chinensis and designated TcDHN1. Sequence alignment and phylogenetic analyses revealed that TcDHN1 encodes a dehydrin protein. Heterologous overexpression of TcDHN1 in Arabidopsis did not affect growth under normal conditions. Under salt, drought, and cold stresses, transgenic lines exhibited higher seed germination rates, longer primary roots, and improved seedling growth compared with wild-type (WT) plants. The transgenic lines showed significantly increased activities of antioxidant enzymes, including superoxide dismutase, catalase, and peroxidase. In addition, ectopic overexpression of TcDHN1 in Arabidopsis conferred enhanced tolerance to abiotic stresses compared to WT plants, accompanied by increased expression of the stress-responsive genes Responsive to Desiccation 29A (AtRD29A) and Heat Shock Protein 70-1 (AtHSP70-1). The above results indicate that TcDHN1 confers enhanced tolerance to abiotic stresses. This study provides a functional characterization of an abiotic stress-responsive gene from recalcitrant seeds and identifies a potential genetic resource for molecular breeding. This could potentially improve abiotic stress resistance in T. chinensis and related medicinal plants.