The plant mitochondrial genome: dynamics and maintenance

Complete mitochondrial genome of Melia azedarach L., reveals two conformations generated by the repeat sequence mediated recombination

Melia azedarach is a species of enormous value of pharmaceutical industries. Although the chloroplast genome of M. azedarach has been explored, the information of mitochondrial genome (Mt genome) remains surprisingly limited. In this study, we used a hybrid assembly strategy of BGI short-reads and Nanopore long-reads to assemble the Mt genome of M. azedarach. The Mt genome of M. azedarach is characterized by two circular chromosomes with 350,142 bp and 290,387 bp in length, respectively, which encodes 35 protein-coding genes (PCGs), 23 tRNA genes, and 3 rRNA genes. A pair of direct repeats (R1 and R2) were associated with genome recombination, resulting in two conformations based on the Sanger sequencing and Oxford Nanopore sequencing. Comparative analysis identified 19 homologous fragments between Mt and chloroplast genome, with the longest fragment of 12,142 bp. The phylogenetic analysis based on PCGs were consist with the latest classification of the Angiosperm Phylogeny Group. Notably, a total of 356 potential RNA editing sites were predicted based on 35 PCGs, and the editing events lead to the formation of the stop codon in the rps10 gene and the start codons in the nad4L and atp9 genes, which were verified by PCR amplification and Sanger sequencing. Taken together, the exploration of M. azedarach gap-free Mt genome provides a new insight into the evolution research and complex mitogenome architecture.

De Novo Hybrid Assembly Unveils Multi-Chromosomal Mitochondrial Genomes in Ludwigia Species, Highlighting Genomic Recombination, Gene Transfer, and RNA Editing Events

Biological invasions have been identified as the fifth cause of biodiversity loss, and their subsequent dispersal represents a major ecological challenge. The aquatic invasive species Ludwigia grandiflora subsp. hexapetala (Lgh) and Ludwigia peploides subsp. montevidensis (Lpm) are largely distributed in aquatic environments in North America and in Europe. However, they also present worrying terrestrial forms that are able to colonize wet meadows. To comprehend the mechanisms of the terrestrial adaptation of Lgh and Lpm, it is necessary to develop their genomic resources, which are currently poorly documented. We performed de novo assembly of the mitogenomes of Lgh and Lpm through hybrid assemblies, combining short reads (SR) and/or long reads (LR) before annotating both mitogenomes. We successfully assembled the mitogenomes of Lgh and Lpm into two circular molecules each, resulting in a combined total length of 711,578 bp and 722,518 bp, respectively. Notably, both the Lgh and Lpm molecules contained plastome-origin sequences, comprising 7.8% of the mitochondrial genome length. Additionally, we identified recombinations that were mediated by large repeats, suggesting the presence of multiple alternative conformations. In conclusion, our study presents the first high-quality mitogenomes of Lpm and Lgh, which are the only ones in the Myrtales order found as two circular molecules.

Insights into structure, codon usage, repeats, and RNA editing of the complete mitochondrial genome of Perilla frutescens (Lamiaceae)

Perilla frutescens (L.) Britton, a member of the Lamiaceae family, stands out as a versatile plant highly valued for its unique aroma and medicinal properties. Additionally, P. frutescens seeds are rich in Îś-linolenic acid, holding substantial economic importance. While the nuclear and chloroplast genomes of P. frutescens have already been documented, the complete mitochondrial genome sequence remains unreported. To this end, the sequencing, annotation, and assembly of the entire Mitochondrial genome of P. frutescens were hereby conducted using a combination of Illumina and PacBio data. The assembled P. frutescens mitochondrial genome spanned 299,551 bp and exhibited a typical circular structure, involving a GC content of 45.23%. Within the genome, a total of 59 unique genes were identified, encompassing 37 protein-coding genes, 20 tRNA genes, and 2 rRNA genes. Additionally, 18 introns were observed in 8 protein-coding genes. Notably, the codons of the P. frutescens mitochondrial genome displayed a notable A/T bias. The analysis also revealed 293 dispersed repeat sequences, 77 simple sequence repeats (SSRs), and 6 tandem repeat sequences. Moreover, RNA editing sites preferentially produced leucine at amino acid editing sites. Furthermore, 70 sequence fragments (12,680 bp) having been transferred from the chloroplast to the mitochondrial genome were identified, accounting for 4.23% of the entire mitochondrial genome. Phylogenetic analysis indicated that among Lamiaceae plants, P. frutescens is most closely related to Salvia miltiorrhiza and Platostoma chinense. Meanwhile, inter-species Ka/Ks results suggested that Ka/Ks < 1 for 28 PCGs, indicating that these genes were evolving under purifying selection. Overall, this study enriches the mitochondrial genome data for P. frutescens and forges a theoretical foundation for future molecular breeding research.

Assembly and comparative analysis of the complete mitochondrial genome of Brassica rapa var. Purpuraria

BACKGROUND

Purple flowering stalk (Brassica rapa var. purpuraria) is a widely cultivated plant with high nutritional and medicinal value and exhibiting strong adaptability during growing. Mitochondrial (mt) play important role in plant cells for energy production, developing with an independent genetic system. Therefore, it is meaningful to assemble and annotate the functions for the mt genome of plants independently. Though there have been several reports referring the mt genome of in Brassica species, the genome of mt in B. rapa var. purpuraria and its functional gene variations when compared to its closely related species has not yet been addressed.

RESULTS

The mt genome of B. rapa var. purpuraria was assembled through the Illumina and Nanopore sequencing platforms, which revealed a length of 219,775 bp with a typical circular structure. The base composition of the whole B. rapa var. purpuraria mt genome revealed A (27.45%), T (27.31%), C (22.91%), and G (22.32%). 59 functional genes, composing of 33 protein-coding genes (PCGs), 23 tRNA genes, and 3 rRNA genes, were annotated. The sequence repeats, codon usage, RNA editing, nucleotide diversity and gene transfer between the cp genome and mt genome were examined in the B. rapa var. purpuraria mt genome. Phylogenetic analysis show that B. rapa var. Purpuraria was closely related to B. rapa subsp. Oleifera and B. juncea. Ka/Ks analysis reflected that most of the PCGs in the B. rapa var. Purpuraria were negatively selected, illustrating that those mt genes were conserved during evolution.

CONCLUSIONS

The results of our findings provide valuable information on the B.rapa var. Purpuraria genome, which might facilitate molecular breeding, genetic variation and evolutionary researches for Brassica species in the future.

Comparative genomic and phylogenetic analyses of mitochondrial genomes of hawthorn (Crataegus spp.) in Northeast China

Hawthorn (Crataegus spp.) plants are major sources of health food and medicines. Twenty species and seven variations of Crataegus are present in China. A variety of unique Crataegus species was found in their natural distribution in northeast China. In the present study, we assembled and annotated the mitochondrial genomes of five Crataegus species from northeastern China. The sizes of the newly sequenced mitochondrial genomes ranged from 245,907 bp to 410,837 bp. A total of 45-55 genes, including 12-19 transfer RNA genes, three ribosomal RNA genes, and 29-33 protein-coding genes (PCGs) were encoded by these mitochondrial genomes. Seven divergent hotspot regions were identified by comparative analyses: atp6, nad3, ccmFN, matR, nad1, nad5, and rps1. The most conserved genes among the Crataegus species, according to the whole-genome correlation analysis, were nad1, matR, nad5, ccmFN, cox1, nad4, trnQ-TTG, trnK-TTT, trnE-TTC, and trnM-CAT. Horizontal gene transfer between organellar genomes was common in Crataegus plants. Based on the phylogenetic trees of mitochondrial PCGs, C. maximowiczii, C. maximowiczii var. ninganensis, and C. bretschneideri shared similar maternal relationships. This study improves Crataegus mitochondrial genome resources and offers important insights into the taxonomy and species identification of this genus.

Comprehensive analysis of the complete mitochondrial genome of Lilium tsingtauense reveals a novel multichromosome structure

KEY MESSAGE

Lilium tsingtauense mitogenome comprises 27 independent chromosome molecules, it undergoes frequent genomic recombination, and the rate of recombination and mutation between different repetitive sequences affects the formation of multichromosomal structures. Given the extremely large genome of Lily, which likely harbors additional genetic resources, it serves as an ideal material for studying the phylogenetic evolution of organisms. Although the Lilium chloroplast genome has been documented, the sequence of its mitochondrial genome (mitogenome) remains uncharted. Using BGI short reads and Nanopore long reads, we sequenced, assembled, and annotated the mitogenome of Lilium tsingtauense. This effort culminated in the characterization of Lilium's first complete mitogenome. Comparative analysis with other angiosperms revealed the unique multichromosomal structure of the L. tsingtauense mitogenome, spanning 1,125,108 bp and comprising 27 independent circular chromosomes. It contains 36 protein-coding genes, 12 tRNA genes, and 3 rRNA genes, with a GC content of 44.90%. Notably, three chromosomes in the L. tsingtauense mitogenome lack identifiable genes, hinting at the potential existence of novel genes and noncoding elements. The high degree of observed genome fragmentation implies frequent reorganization, with recombination and mutation rates among diverse repetitive sequences likely driving the formation of multichromosomal structures. Our comprehensive analysis, covering genome size, coding genes, structure, RNA editing, repetitive sequences, and sequence migration, sheds light on the evolutionary and molecular biology of multichromosomal mitochondria in Lilium. This high-quality mitogenome of L. tsingtauense not only enriches our understanding of multichromosomal mitogenomes but also establishes a solid foundation for future genome breeding and germplasm innovation in Lilium.

The Arabidopsis Mitochondrial Nucleoid-Associated Protein WHIRLY2 Is Required for a Proper Response to Salt Stress

In the last years, plant organelles have emerged as central coordinators of responses to internal and external stimuli, which can induce stress. Mitochondria play a fundamental role as stress sensors being part of a complex communication network between the organelles and the nucleus. Among the different environmental stresses, salt stress poses a significant challenge and requires efficient signaling and protective mechanisms. By using the why2 T-DNA insertion mutant and a novel knock-out mutant prepared by CRISPR/Cas9-mediated genome editing, this study revealed that WHIRLY2 is crucial for protecting mitochondrial DNA (mtDNA) integrity during salt stress. Loss-of-function mutants show an enhanced sensitivity to salt stress. The disruption of WHIRLY2 causes the impairment of mtDNA repair that results in the accumulation of aberrant recombination products, coinciding with severe alterations in nucleoid integrity and overall mitochondria morphology besides a compromised redox-dependent response and misregulation of antioxidant enzymes. The results of this study revealed that WHIRLY2-mediated structural features in mitochondria (nucleoid compactness and cristae) are important for an effective response to salt stress.

De novo assembly of the complete mitochondrial genome of pepino (Solanum muricatum) using PacBio HiFi sequencing: insights into structure, phylogenetic implications, and RNA editing

BACKGROUND

Solanum muricatum is an emerging horticultural fruit crop with rich nutritional and antioxidant properties. Although the chromosome-scale genome of this species has been sequenced, its mitochondrial genome sequence has not been reported to date.

RESULTS

PacBio HiFi sequencing was used to assemble the circular mitogenome of S. muricatum, which was 433,466 bp in length. In total, 38 protein-coding, 19 tRNA, and 3 rRNA genes were annotated. The reticulate mitochondrial conformations with multiple junctions were verified by polymerase chain reaction, and codon usage, sequence repeats, and gene migration from chloroplast to mitochondrial genome were determined. A collinearity analysis of eight Solanum mitogenomes revealed high structural variability. Overall, 585 RNA editing sites in protein coding genes were identified based on RNA-seq data. Among them, mttB was the most frequently edited (52 times), followed by ccmB (46 times). A phylogenetic analysis based on the S. muricatum mitogenome and those of 39 other taxa (including 25 Solanaceae species) revealed the evolutionary and taxonomic status of S. muricatum.

CONCLUSIONS

We provide the first report of the assembled and annotated S. muricatum mitogenome. This information will help to lay the groundwork for future research on the evolutionary biology of Solanaceae species. Furthermore, the results will assist the development of molecular breeding strategies for S. muricatum based on the most beneficial agronomic traits of this species.

Assembly and comparative analysis of the complete mitochondrial genome of white towel gourd (Luffa cylindrica)

Mitochondria play an important role in the energy production of plant cells through independent genetic systems. This study has aimed to assemble and annotate the functions of the mitochondrial (mt) genome of Luffa cylindrica. The mt genome of L. cylindrica contained two chromosomes with lengths of 380,879 bp and 67,982 bp, respectively. Seventy-seven genes including 39 protein-coding genes, 34 tRNA genes, 3 rRNA genes, and 1 pseudogene, were identified. About 90.63% of the codons ended with A or U bases, and 98.63% of monomers contained A/T, which contributed to the high A/T content (55.91%) of the complete mt genome. Six genes (ATP8, CCMFC, NAD4, RPL10, RPL5 and RPS4) showed positive selection. Phylogenetic analysis indicates that L. cylindrica is closely related to L. acutangula. The present results provide the mt genome of L. cylindrica, which may facilitate possible genetic variation, evolutionary, and molecular breeding studies of L. cylindrica.

Dynamic changes in the plastid and mitochondrial genomes of the angiosperm Corydalis pauciovulata (Papaveraceae)

BACKGROUND

Corydalis DC., the largest genus in the family Papaveraceae, comprises > 465 species. Complete plastid genomes (plastomes) of Corydalis show evolutionary changes, including syntenic arrangements, gene losses and duplications, and IR boundary shifts. However, little is known about the evolution of the mitochondrial genome (mitogenome) in Corydalis. Both the organelle genomes and transcriptomes are needed to better understand the relationships between the patterns of evolution in mitochondrial and plastid genomes.

RESULTS

We obtained complete plastid and mitochondrial genomes from Corydalis pauciovulata using a hybrid assembly of Illumina and Oxford Nanopore Technologies reads to assess the evolutionary parallels between the organelle genomes. The mitogenome and plastome of C. pauciovulata had sizes of 675,483 bp and 185,814 bp, respectively. Three ancestral gene clusters were missing from the mitogenome, and expanded IR (46,060 bp) and miniaturized SSC (202 bp) regions were identified in the plastome. The mitogenome and plastome of C. pauciovulata contained 41 and 67 protein-coding genes, respectively; the loss of genes was a plastid-specific event. We also generated a draft genome and transcriptome for C. pauciovulata. A combination of genomic and transcriptomic data supported the functional replacement of acetyl-CoA carboxylase subunit β (accD) by intracellular transfer to the nucleus in C. pauciovulata. In contrast, our analyses suggested a concurrent loss of the NADH-plastoquinone oxidoreductase (ndh) complex in both the nuclear and plastid genomes. Finally, we performed genomic and transcriptomic analyses to characterize DNA replication, recombination, and repair (DNA-RRR) genes in C. pauciovulata as well as the transcriptomes of Liriodendron tulipifera and Nelumbo nuicifera. We obtained 25 DNA-RRR genes and identified their structure in C. pauciovulata. Pairwise comparisons of nonsynonymous (dN) and synonymous (dS) substitution rates revealed that several DNA-RRR genes in C. pauciovulata have higher dN and dS values than those in N. nuicifera.

CONCLUSIONS

The C. pauciovulata genomic data generated here provide a valuable resource for understanding the evolution of Corydalis organelle genomes. The first mitogenome of Papaveraceae provides an example that can be explored by other researchers sequencing the mitogenomes of related plants. Our results also provide fundamental information about DNA-RRR genes in Corydalis and their related rate variation, which elucidates the relationships between DNA-RRR genes and organelle genome stability.

A High-Quality Assembly and Comparative Analysis of the Mitogenome of Actinidia macrosperma

The mitochondrial genome (mitogenome) of Actinidia macrosperma, a traditional medicinal plant within the Actinidia genus, remains relatively understudied. This study aimed to sequence the mitogenome of A. macrosperma, determining its assembly, informational content, and developmental expression. The results revealed that the mitogenome of A. macrosperma is circular, spanning 752,501 bp with a GC content of 46.16%. It comprises 63 unique genes, including 39 protein-coding genes (PCGs), 23 tRNA genes, and three rRNA genes. Moreover, the mitogenome was found to contain 63 SSRs, predominantly mono-nucleotides, as well as 25 tandem repeats and 650 pairs of dispersed repeats, each with lengths equal to or greater than 60, mainly comprising forward repeats and palindromic repeats. Moreover, 53 homologous fragments were identified between the mitogenome and chloroplast genome (cp-genome), with the longest segment measuring 4296 bp. This study represents the initial report on the mitogenome of the A. macrosperma, providing crucial genetic materials for phylogenetic research within the Actinidia genus and promoting the exploitation of species genetic resources.

Assembly and comparative analysis of the initial complete mitochondrial genome of Primulina hunanensis (Gesneriaceae): a cave-dwelling endangered plant

BACKGROUND

Primulina hunanensis, a troglobitic plant within the Primulina genus of Gesneriaceae family, exhibits robust resilience to arid conditions and holds great horticultural potential as an ornamental plant. The work of chloroplast genome (cpDNA) has been recently accomplished, however, the mitochondrial genome (mtDNA) that is crucial for plant evolution has not been reported.

RESULTS

In this study, we sequenced and assembled the P. hunanensis complete mtDNA, and elucidated its evolutionary and phylogenetic relationships. The assembled mtDNA spans 575,242 bp with 43.54% GC content, encompassing 60 genes, including 37 protein-coding genes (PCGs), 20 tRNA genes, and 3 rRNA genes. Notably, high number of repetitive sequences in the mtDNA and substantial sequence translocation from chloroplasts to mitochondria were observed. To determine the evolutionary and taxonomic positioning of P. hunanensis, a phylogenetic tree was constructed using mitochondrial PCGs from P. hunanensis and 32 other taxa. Furthermore, an exploration of PCGs relative synonymous codon usage, identification of RNA editing events, and an investigation of collinearity with closely related species were conducted.

CONCLUSIONS

This study reports the initial assembly and annotation of P. hunanensis mtDNA, contributing to the limited mtDNA repository for Gesneriaceae plants and advancing our understanding of their evolution for improved utilization and conservation.

Mitochondrial genome features and systematic evolution of diospyros kaki thunb 'Taishuu'

BACKGROUND

'Taishuu' has a crisp texture, abundant juice, and sweet flavor with hints of cantaloupe. The availability of mitochondrial genome data of Diospyros species is far from the known number of species.

RESULTS

The sequencing data were assembled into a closed circular mitochondrial chromosome with a 421,308 bp length and a 45.79% GC content. The mitochondrial genome comprised 40 protein-coding, 24 tRNA, and three rRNA genes. The most common codons for arginine (Arg), proline (Pro), glycine (Gly), tryptophan (Trp), valine (Val), alanine (Ala), and leucine (Leu) were AGA, CCA, GGA, UGG, GUA, GCA, and CUA, respectively. The start codon for cox1 and nad4L protein-coding genes was ACG (ATG), whereas the remaining protein-coding genes started with ATG. There are four types of stop codons: CGA, TAA, TAG, and TGA, with TAA being the most frequently used stop codon (45.24%). In the D. kaki Thunb. 'Taishuu' mitochondrial genome, a total of 645 repeat sequences were identified, including 125 SSRs, 7 tandem repeats, and 513 dispersed repeats. Collinearity analysis revealed a close relationship between D. kaki Thunb. 'Taishuu' and Diospyros oleifera, with conserved homologous gene fragments shared among these species in large regions of the mitochondrial genome. The protein-coding genes ccmB and nad4L were observed to undergo positive selection. Analysis of homologous sequences between chloroplasts and mitochondria identified 28 homologous segments, with a total length of 24,075 bp, accounting for 5.71% of the mitochondrial genome. These homologous segments contain 8 annotated genes, including 6 tRNA genes and 2 protein-coding genes (rrn18 and ccmC). There are 23 homologous genes between chloroplasts and nuclei. Mitochondria, chloroplasts, and nuclei share two homologous genes, which are trnV-GAC and trnW-CCA.

CONCLUSION

In conclusion, a high-quality chromosome-level draft genome for D. kaki was generated in this study, which will contribute to further studies of major economic traits in the genus Diospyros.

Collective mitochondrial dynamics resolve conflicting cellular tensions: From plants to general principles

Mitochondria play diverse and essential roles in eukaryotic cells, and plants are no exception. Plant mitochondria have several differences from their metazoan and fungal cousins: they often exist in a fragmented state, move rapidly on actin rather than microtubules, have many plant-specific metabolic features and roles, and usually contain only a subset of the complete mtDNA genome, which itself undergoes frequent recombination. This arrangement means that exchange and complementation is essential for plant mitochondria, and recent work has begun to reveal how their collective dynamics and resultant "social networks" of encounters support this exchange, connecting plant mitochondria in time rather than in space. This review will argue that this social network perspective can be extended to a "societal network", where mitochondrial dynamics are an essential part of the interacting cellular society of organelles and biomolecules. Evidence is emerging that mitochondrial dynamics allow optimal resolutions to competing cellular priorities; we will survey this evidence and review potential future research directions, highlighting that plant mitochondria can help reveal and test principles that apply across other kingdoms of life. In parallel with this fundamental cell biology, we also highlight the translational "One Health" importance of plant mitochondrial behaviour - which is exploited in the production of a vast amount of crops consumed worldwide - and the potential for multi-objective optimisation to understand and rationally re-engineer the evolved resolutions to these tensions.

Three complete chloroplast genomes from two north American Rhus species and phylogenomics of Anacardiaceae

BACKGROUND

The suamc genus Rhus (sensu stricto) includes two subgenera, Lobadium (ca. 25 spp.) and Rhus (ca. 10 spp.). Their members, R. glabra and R. typhina (Rosanae: Sapindales: Anacardiaceae), are two economic important species. Chloroplast genome information is of great significance for the study of plant phylogeny and taxonomy.

RESULTS

The three complete chloroplast genomes from two Rhus glabra and one R. typhina accessions were obtained with a total of each about 159k bp in length including a large single-copy region (LSC, about 88k bp), a small single-copy regions (SSC, about 19k bp) and a pair of inverted repeats regions (IRa/IRb, about 26k bp), to form a canonical quadripartite structure. Each genome contained 88 protein-coding genes, 37 transfer RNA genes, eight ribosomal RNA genes and two pseudogenes. The overall GC content of the three genomes all were same (37.8%), and RSCU values showed that they all had the same codon prefers, i.e., to use codon ended with A/U (93%) except termination codon. Three variable hotspots, i.e., ycf4-cemA, ndhF-rpl32-trnL and ccsA-ndhD, and a total of 152-156 simple sequence repeats (SSR) were identified. The nonsynonymous (Ka)/synonymous (Ks) ratio was calculated, and cemA and ycf2 genes are important indicators of gene evolution. The phylogenetic analyses of the family Anacardiaceae showed that the eight genera were grouped into three clusters, and supported the monophyly of the subfamilies and all the genera. The accessions of five Rhus species formed four clusters, while, one individual of R. typhina grouped with the R. glabra accessions instead of clustering into the two other individuals of R. typhina in the subgenus Rhus, which showed a paraphyletic relationship.

CONCLUSIONS

Comparing the complete chloroplast genomes of the Rhus species, it was found that most SSRs were A/T rich and located in the intergenic spacer, and the nucleotide divergence exhibited higher levels in the non-coding region than in the coding region. The Ka/Ks ratio of cemA gene was > 1 for species collected in America, while it was < 1 for other species in China, which dedicated that the Rhus species from North America and East Asia have different evolutionary pressure. The phylogenetic analysis of the complete chloroplast genome clarified the Rhus placement and relationship. The results obtained in this study are expected to provide valuable genetic resources to perform species identification, molecular breeding, and intraspecific diversity of the Rhus species.

The complete mitochondrial genome of Aglaia odorata, insights into its genomic structure and RNA editing sites

Aglaia odorata, native to Guangdong, Guangxi, and Hainan provinces in China, has long been utilized as an herbal remedy in ancient China. In this study, we assembled and annotated the complete mitochondrial genome (mitogenome) of A. odorata, which spans a total length of 537,321 bp. Conformation of the A. odorata recombination was verified through PCR experiments and Sanger sequencing. We identified and annotated 35 protein-coding genes (PCGs), 22 tRNA genes, and 3 rRNA genes within the mitogenome. Analysis of repeated elements revealed the presence of 192 SSRs, 29 pairs of tandem repeats, and 333 pairs of dispersed repeats in the A. odorata mitogenome. Additionally, we analyzed codon usage and mitochondrial plastid DNAs (MTPTs). Twelve MTPTs between the plastome and mitogenome of A. odorata were identified, with a combined length of 2,501 bp, accounting for 0.47% of the mitogenome. Furthermore, 359 high-confidence C to U RNA editing sites were predicted on PCGs, and four selected RNA editing sites were specially examined to verify the creation of start and/or stop codons. Extensive genomic rearrangement was observed between A. odorata and related mitogenomes. Phylogenetic analysis based on mitochondrial PCGs were conducted to elucidate the evolutionary relationships between A. odorata and other angiosperms.

RNA editing events and expression profiles of mitochondrial protein-coding genes in the endemic and endangered medicinal plant, Corydalis saxicola

Corydalis saxicola, an endangered medicinal plant endemic to karst habitats, is widely used in Traditional Chinese Medicine to treat hepatitis, abdominal pain, bleeding hemorrhoids and other conditions. However, to date, the mitochondrial (mt) genome of C. saxicola has not been reported, which limits our understanding of the genetic and biological mechanisms of C. saxicola. Here, the mt genome of C. saxicola was assembled by combining the Nanopore and Illumina reads. The mt genome of C. saxicola is represented by a circular chromosome which is 587,939 bp in length, with an overall GC content of 46.50%. 40 unique protein-coding genes (PCGs), 22 tRNA genes and three rRNA genes were identified. Codon usage of the PCGs was investigated and 167 simple sequence repeats were identified. Twelve homologous fragments were identified between the mt and ct genomes of C. saxicola, accounting for 1.04% of the entire mt genome. Phylogenetic examination of the mt genomes of C. saxicola and 30 other taxa provided an understanding of their evolutionary relationships. We also predicted 779 RNA editing sites in 40 C. saxicola mt PCGs and successfully validated 506 (65%) of these using PCR amplification and Sanger sequencing. In addition, we transcriptionally profiled 24 core mt PCGs in C. saxicola roots treated with different concentrations of CaCl2, as well as in other organs. These investigations will be useful for effective utilization and molecular breeding, and will also provide a reference for further studies of the genus Corydalis.

Characteristics of chloroplast and mitochondrial genomes and intracellular gene transfer in the Korean endemic shrub, Sophora koreensis Nakai (Fabaceae)

Sophora koreensis Nakai, an endemic species distributed only in the Korean Peninsula, is of great geographical, economic, and taxonomic importance. Although its complete chloroplast (cp) genome sequence has been reported, its mitochondrial (mt) genome sequence has not yet been studied. Therefore, in this study, we aimed to investigate its mt genome sequence and compare it with those reported for other Fabaceae species. Total genomic DNA was extracted from fresh S. koreensis leaves collected from natural habitats in Gangwon-do Province, South Korea. This was followed by polymerase chain reaction (PCR) amplification of cpDNA insertions in the mt genome and the detection of microsatellites and dispersed repeats in the cp and mt genomes. Finally, the cp and mt genomes of S. koreensis were compared with those reported for other Fabaceae species. The cp sequence of S. koreensis showed identical gene orders and contents as those previously reported. Only six substitutions and one deletion were detected with 99 % homology. Conversely, the complete mt genome sequence, which was 517,845 bp in length and encoded 61 genes, including 43 protein-coding, 15 transfer RNAs, and 3 ribosomal RNA genes, was considerably different from that of S. japonica in terms of gene order and composition. Further, the mt genome of S. koreensis included ca. 7 and 3 kb insertions, representing an intracellular gene transfer (IGT) event, and the regions with these insertions were determined to be originally present in the cp genome. This IGT event was also confirmed via PCR amplification. IGT events can be induced via biological gene expression control or the use of repetitive sequences, and they provide important insights into the evolutionary lineage of S. koreensis. However, further studies are needed to clarify the gene transfer mechanisms between the two organelles.

Characterization of the Complete Mitochondrial Genome of Wintersweet (Chimonanthus praecox) and Comparative Analysis within Magnoliids

Mitochondrial genome sequencing is a valuable tool for investigating mitogenome evolution, species phylogeny, and population genetics. Chimonanthus praecox (L.) Link, also known as "La Mei" in Chinese, is a famous ornamental and medical shrub belonging to the order Laurales of the Calycanthaceae family. Although the nuclear genomes and chloroplast genomes of certain Laurales representatives, such as Lindera glauca, Laurus nobilis, and Piper nigrum, have been sequenced, the mitochondrial genome of Laurales members remains unknown. Here, we reported the first complete mitogenome of C. praecox. The mitogenome was 972,347 bp in length and comprised 60 unique coding genes, including 40 protein-coding genes (PCGs), 17 tRNA genes, and three rRNA genes. The skewness of the PCGs showed that the AT skew (-0.0096233) was negative, while the GC skew (0.031656) was positive, indicating higher contents of T's and G's in the mitochondrial genome of C. praecox. The Ka/Ks ratio analysis showed that the Ka/Ks values of most genes were less than one, suggesting that these genes were under purifying selection. Furthermore, there is a substantial abundance of dispersed repeats in C. praecox, constituting 16.98% of the total mitochondrial genome. A total of 731 SSR repeats were identified in the mitogenome, the highest number among the eleven available magnoliids mitogenomes. The mitochondrial phylogenetic analysis based on 29 conserved PCGs placed the C. praecox in Lauraceae, and supported the sister relationship of Laurales with Magnoliales, which was congruent with the nuclear genome evidence. The present study enriches the mitogenome data of C. praecox and promotes further studies on phylogeny and plastid evolution.

Mitochondrial genome of Hancornia speciosa gomes: intergenic regions containing retrotransposons and predicted genes

BACKGROUND

Plant mitochondrial genomes are characterized by high homologous recombination, extensive intergenic spacers, conservation in DNA sequences, and gene content. The Hancornia genus belongs to the Apocynaceae family, with H. speciosa Gomes being the sole species in the genus. It is an siganificant commercial fruit crop; however, only a number of studies have been conducted. In this study, we present the mitochondrial genome of H. speciosa and compare it with other mitochondrial genomes within the Apocynaceae family.

METHODS AND RESULTS

A total of 2.8 Gb of Illumina paired-end reads were used to obtain the mitogenome, resulting in 22 contigs that were merged using 6.1 Gb of Illumina mate-pair reads to obtain a circular chromosome. The mitochondrial genome of H. speciosa is circular, containing 63 predicted functional genes, spanning a length of 741,811 bp, with a CG content of 44%. Within the mitogenome, 50 chloroplast DNA sequences, equivalent to 1.72% of the genome, were detected. However, intergenic spaces accounted for 703,139 bp (94.79% of the genome), and 287 genes were predicted, totaling 173,721 bp.

CONCLUSION

This suggests the incorporation of nuclear DNA into the mitogenome of H. speciosa and self duplication. Comparative analysis among the mitogenomes in the Apocynaceae family revealed a diversity in the structure mediated by recombination, with similar gene content and large intergenic spaces.

Comprehensive Analysis of the Complete Mitochondrial Genome of Rehmannia chingii: An Autotrophic Species in the Orobanchaceae Family

Rehmannia chingii is an important medicinal plant with immense value in scientific research. However, its mitochondrial genome (mitogenome) has not yet been characterized. Herein, based on whole-genome Illumina short reads and PacBio HiFi reads, we obtained the complete mitogenome of R. chingii through a de novo assembly strategy. We carried out comparative genomic analyses and found that, in comparison with the plastid genome (plastome) showing a high degree of structural conservation, the R. chingii mitogenome structure is relatively complex, showing an intricate ring structure with 16 connections, owing to five repetitive sequences. The R. chingii mitogenome was 783,161 bp with a GC content of 44.8% and contained 77 genes, comprising 47 protein-coding genes (CDS), 27 tRNA genes, and 3 rRNA genes. We counted 579 RNA editing events in 47 CDS and 12,828 codons in all CDSs of the R. chingii mitogenome. Furthermore, 24 unique sequence transfer fragments were found between the mitogenome and plastome, comprising 8 mitogenome CDS genes and 16 plastome CDS genes, corresponding to 2.39% of the R. chingii mitogenome. Mitogenomes had shorter but more collinear regions, evidenced by a comparison of the organelles of non-parasitic R. chingii, hemiparasitic Pedicularis chinensis, and holoparasitic Aeginetia indica in the Orobanchaceae family. Moreover, from non-parasitic to holoparasitic species, the genome size in the mitogenomes of Orobanchaceae species did not decrease gradually. Instead, the smallest mitogenome was found in the hemiparasitic species P. chinensis, with a size of 225,612 bp. The findings fill the gap in the mitogenome research of the medicinal plant R. chingii, promote the progress of the organelle genome research of the Orobanchaceae family, and provide clues for molecular breeding.

Remarkable mitochondrial genome heterogeneity in Meniocus linifolius (Brassicaceae)

KEY MESSAGE

Detailed analyses of 16 genomes identified a remarkable acceleration of mutation rate, hence mitochondrial sequence and structural heterogeneity, in Meniocus linifolius (Brassicaceae). The powerhouse, mitochondria, in plants feature high levels of structural variation, while the encoded genes are normally conserved. However, the substitution rates and spectra of mitochondria DNA within the Brassicaceae, a family with substantial scientific and economic importance, have not been adequately deciphered. Here, by analyzing three newly assembled and 13 known mitochondrial genomes (mitogenomes), we report the highly variable genome structure and mutation rates in Brassicaceae. The genome sizes and GC contents are 196,604 bp and 46.83%, 288,122 bp and 44.79%, and 287,054 bp and 44.93%, for Meniocus linifolius (Mli), Crucihimalaya lasiocarpa (Cla), and Lepidium sativum (Lsa), respectively. In total, 29, 33, and 34 protein-coding genes (PCGs) and 14, 18, and 18 tRNAs are annotated for Mli, Cla, and Lsa, respectively, while all mitogenomes contain one complete circular molecule with three rRNAs and abundant RNA editing sites. The Mli mitogenome features four conformations likely mediated by the two pairs of long repeats, while at the same time seems to have an unusual evolutionary history due to higher GC content, loss of more genes and sequences, but having more repeats and plastid DNA insertions. Corroborating with these, an ambiguous phylogenetic position with long branch length and elevated synonymous substitution rate in nearly all PCGs are observed for Mli. Taken together, our results reveal a high level of mitogenome heterogeneity at the family level and provide valuable resources for further understanding the evolutionary pattern of organelle genomes in Brassicaceae.

Stochastic organelle genome segregation through Arabidopsis development and reproduction

Organelle DNA (oDNA) in mitochondria and plastids is vital for plant (and eukaryotic) life. Selection against damaged oDNA is mediated in part by segregation - sorting different oDNA types into different cells in the germline. Plants segregate oDNA very rapidly, with oDNA recombination protein MSH1 a key driver of this segregation, but we have limited knowledge of the dynamics of this segregation within plants and between generations. Here, we reveal how oDNA evolves through Arabidopsis thaliana development and reproduction. We combine stochastic modelling, Bayesian inference, and model selection with new and existing tissue-specific oDNA measurements from heteroplasmic Arabidopsis plant lines through development and between generations. Segregation proceeds gradually but continually during plant development, with a more rapid increase between inflorescence formation and the next generation. When MSH1 is compromised, the majority of observed segregation can be achieved through partitioning at cell divisions. When MSH1 is functional, mtDNA segregation is far more rapid; we show that increased oDNA gene conversion is a plausible mechanism quantitatively explaining this acceleration. These findings reveal the quantitative, time-dependent details of oDNA segregation in Arabidopsis. We also discuss the support for different models of the plant germline provided by these observations.

Complete mitochondrial genome of the endangered Prunus pedunculata (Prunoideae, Rosaceae) in China: characterization and phylogenetic analysis

Introduction

Prunus pedunculata (Prunoideae: Rosaceae), a relic shrub with strong resistance and multiple application values, is endangered in China. Extensive research had been devoted to gene expression, molecular markers, plastid genome analysis, and genetic background investigations of P. pedunculata. However, the mitochondrial genome of this species has not been systematically described, owing to the complexity of the plant mitogenome.

Methods

In the present research, the complete mitochondrial genome of P. pedunculata was assembled, annotated, and characterized. The genomic features, gene content and repetitive sequences were analyzed. The genomic variation and phylogenetic analysis have been extensively enumerated.

Results and discussion

The P. pedunculata mitogenome is a circular molecule with a total length of 405,855 bp and a GC content of 45.63%, which are the smallest size and highest GC content among the known Prunus mitochondrial genomes. The mitogenome of P. pedunculata encodes 62 genes, including 34 unique protein-coding genes (PCGs, excluding three possible pseudogenes), three ribosomal RNA genes, and 19 transfer RNA genes. The mitogenome is rich in repetitive sequences, counting 112 simple sequence repeats, 15 tandem repeats, and 50 interspersed repetitive sequences, with a total repeat length of 11,793 bp, accounting for 2.91% of the complete genome. Leucine (Leu) was a predominant amino acid in PCGs, with a frequency of 10.67%, whereas cysteine (Cys) and tryptophan (Trp) were the least adopted. The most frequently used codon was UUU (Phe), with a relative synonymous codon usage (RSCU) value of 1.12. Selective pressure was calculated based on 20 shared PCGs in the mitogenomes of the 32 species, most of which were subjected to purifying selection (Ka/Ks < 1), whereas ccmC and ccmFn underwent positive selection. A total of 262 potential RNA editing sites in 26 PCGs were identified. Furthermore, 56 chloroplast-derived fragments were ascertained in the mitogenome, ranging from 30 to 858 bp, and were mainly located across IGS (intergenic spacer) regions or rRNA genes. These findings verify the occurrence of intracellular gene transfer events from the chloroplast to the mitochondria. Furthermore, the phylogenetic relationship of P. pedunculata was supported by the mitogenome data of 30 other taxa of the Rosaceae family. Understanding the mitochondrial genome characteristics of P. pedunculata is of great importance to promote comprehension of its genetic background and this study provides a basis for the genetic breeding of Prunus.

Mitochondrial genome diversity across the subphylum Saccharomycotina

Introduction

Eukaryotic life depends on the functional elements encoded by both the nuclear genome and organellar genomes, such as those contained within the mitochondria. The content, size, and structure of the mitochondrial genome varies across organisms with potentially large implications for phenotypic variance and resulting evolutionary trajectories. Among yeasts in the subphylum Saccharomycotina, extensive differences have been observed in various species relative to the model yeast Saccharomyces cerevisiae, but mitochondrial genome sampling across many groups has been scarce, even as hundreds of nuclear genomes have become available.

Methods

By extracting mitochondrial assemblies from existing short-read genome sequence datasets, we have greatly expanded both the number of available genomes and the coverage across sparsely sampled clades.

Results

Comparison of 353 yeast mitochondrial genomes revealed that, while size and GC content were fairly consistent across species, those in the genera Metschnikowia and Saccharomyces trended larger, while several species in the order Saccharomycetales, which includes S. cerevisiae, exhibited lower GC content. Extreme examples for both size and GC content were scattered throughout the subphylum. All mitochondrial genomes shared a core set of protein-coding genes for Complexes III, IV, and V, but they varied in the presence or absence of mitochondrially-encoded canonical Complex I genes. We traced the loss of Complex I genes to a major event in the ancestor of the orders Saccharomycetales and Saccharomycodales, but we also observed several independent losses in the orders Phaffomycetales, Pichiales, and Dipodascales. In contrast to prior hypotheses based on smaller-scale datasets, comparison of evolutionary rates in protein-coding genes showed no bias towards elevated rates among aerobically fermenting (Crabtree/Warburg-positive) yeasts. Mitochondrial introns were widely distributed, but they were highly enriched in some groups. The majority of mitochondrial introns were poorly conserved within groups, but several were shared within groups, between groups, and even across taxonomic orders, which is consistent with horizontal gene transfer, likely involving homing endonucleases acting as selfish elements.

Discussion

As the number of available fungal nuclear genomes continues to expand, the methods described here to retrieve mitochondrial genome sequences from these datasets will prove invaluable to ensuring that studies of fungal mitochondrial genomes keep pace with their nuclear counterparts.

Diversity and Evolution of Mitochondrial Translation Apparatus

The evolution of mitochondria has proceeded independently in different eukaryotic lines, which is reflected in the diversity of mitochondrial genomes and mechanisms of their expression in eukaryotic species. Mitochondria have lost most of bacterial ancestor genes by transferring them to the nucleus or eliminating them. However, mitochondria of almost all eukaryotic cells still retain relatively small genomes, as well as their replication, transcription, and translation apparatuses. The dependence on the nuclear genome, specific features of mitochondrial transcripts, and synthesis of highly hydrophobic membrane proteins in the mitochondria have led to significant changes in the translation apparatus inherited from the bacterial ancestor, which retained the basic structure necessary for protein synthesis but became more specialized and labile. In this review, we discuss specific properties of translation initiation in the mitochondria and how the evolution of mitochondria affected the functions of main factors initiating protein biosynthesis in these organelles.

Comprehensive assembly and comparative examination of the full mitochondrial genome in Castanea mollissima Blume

The Chinese chestnut, Castanea mollissima Blume, a nut-bearing tree native to China and North Korea, belongs to the Fagaceae family. As an important genetic resource, C. mollissima is vital in enhancing edible chestnut varieties and offers significant insights into the origin and evolution of chestnut species. While the chloroplast genome of C. mollissima has been sequenced, its mitochondrial genome (mitogenome) remains largely uncharted. In this study, we have characterized the C. mollissima mitogenome, assembling it utilizing reads from both BGI and Nanopore sequencing platforms, and conducted a comparative analysis with the mitochondrial genomes of closely related species. The mitogenome of C. mollissima manifests a polycyclic structure consisting of two circular molecules measuring 363,232 bp and 24,806 bp, respectively. This genome encompasses 35 unique protein-coding genes, 19 tRNA genes, and three rRNA genes. A total of 139 SSRs were identified throughout the entire C. mollissima mitogenome. Furthermore, the combined length of homologous fragments between the chloroplast and mitochondrial genomes was 5766 bp, constituting 1.49% of the mitogenome. We also predicted 484 RNA editing sites in C. mollissima, demonstrating C-to-U RNA editing. Phylogenetic analysis of related species' mitogenomes showed that C. mollissima was closely related to Lithocarpus litseifolius (Hance) Chun and Quercus acutissima Carruth. Interestingly, the mitogenome sequences of C. mollissima, L. litseifolius, Q. acutissima, Fagus sylvatica L., and Juglans mandshurica Maxim did not show conservation in their alignments, indicating frequent genome reorganization. This report marks the inaugural study of the C. mollissima mitogenome, serving as a benchmark genome for economically significant plants within the Castanea genus. Moreover, it supplies invaluable information that can guide future molecular breeding efforts and contribute to the broader understanding of chestnut genomics.

Complete Mitochondrial Genome Assembly of an Upland Wild Rice Species, Oryza granulata and Comparative Mitochondrial Genomic Analyses of the Genus Oryza

Wild upland rice species, including Oryza granulata, possess unique characteristics that distinguish them from other Oryza species. For instance, O. granulata characteristically has a GG genome and is accordingly classified as a basal lineage of the genus Oryza. Here, we deployed a versatile hybrid approach by integrating Illumina and PacBio sequencing data to generate a high-quality mitochondrial genome (mitogenome) assembly for O. granulata. The mitogenome of O. granulata was 509,311 base pairs (bp) with sixty-seven genes comprising two circular chromosomes, five ribosomal RNA (rRNA) coding genes, twenty-five transfer RNA (tRNA) coding genes, and thirty-seven genes coding for proteins. We identified a total of 378 simple sequence repeats (SSRs). The genome also contained 643 pairs of dispersed repeats comprising 340 palindromic and 303 forward. In the O. granulata mitogenome, the length of 57 homologous fragments in the chloroplast genome occupied 5.96% of the mitogenome length. Collinearity analysis of three Oryza mitogenomes revealed high structural variability and frequent rearrangements. Phylogenetic analysis showed that, compared to other related genera, O. granulata had the closest genetic relationship with mitogenomes reported for all members of Oryza, and occupies a position at the base of the Oryza phylogeny. Comparative analysis of complete mitochondrial genome assemblies for Oryza species revealed high levels of mitogenomic diversity, providing a foundation for future conservation and utilization of wild rice biodiversity.

Assembly and comparative analysis of the complete mitochondrial genome of Viburnum chinshanense

BACKGROUND

Viburnum chinshanense is an endemic species found exclusively in the North-Central and South-Central regions of China. This species is a lush garden ornamental tree and is extensively utilized for vegetation restoration in rocky desertification areas.

RESULTS

In this study, we obtained 13.96 Gb of Oxford Nanopore data for the whole genome, and subsequently, by combining Illumina short-reads, we successfully assembled the complete mitochondrial genome (mitogenome) of the V. chinshanense using a hybrid assembly strategy. The assembled genome can be described as a circular genome. The total length of the V. chinshanense mitogenome measures 643,971 bp, with a GC content of 46.18%. Our annotation efforts have revealed a total of 39 protein-coding genes (PCGs), 28 tRNA genes, and 3 rRNA genes within the V. chinshanense mitogenome. The analysis of repeated elements has identified 212 SSRs, 19 long tandem repeat elements, and 325 pairs of dispersed repeats in the V. chinshanense mitogenome. Additionally, we have investigated mitochondrial plastid DNAs (MTPTs) and identified 21 MTPTs within the mitogenome and plastidial genome. These MTPTs collectively span a length of 9,902 bp, accounting for 1.54% of the mitogenome. Moreover, employing Deepred-mt, we have confidently predicted 623 C to U RNA editing sites across the 39 protein-coding genes. Furthermore, extensive genomic rearrangements have been observed between V. chinshanense and the mitogenomes of related species. Interestingly, we have also identified a bacterial-derived tRNA gene (trnC-GCA) in the V. chinshanense mitogenome. Lastly, we have inferred the phylogenetic relationships of V. chinshanense with other angiosperms based on mitochondrial PCGs.

CONCLUSIONS

This study marks the first report of a mitogenome from the Viburnum genus, offering a valuable genomic resource for exploring the evolution of mitogenomes within the Dipsacales order.

Genetic diversity of Coffea arabica L. mitochondrial genomes caused by repeat- mediated recombination and RNA editing

Background

Coffea arabica L. is one of the most important crops widely cultivated in 70 countries across Asia, Africa, and Latin America. Mitochondria are essential organelles that play critical roles in cellular respiration, metabolism, and differentiation. C. arabica's nuclear and chloroplast genomes have been reported. However, its mitochondrial genome remained unreported. Here, we intended to sequence and characterize its mitochondrial genome to maximize the potential of its genomes for evolutionary studies, molecular breeding, and molecular marker developments.

Results

We sequenced the total DNA of C. arabica using Illumina and Nanopore platforms. We then assembled the mitochondrial genome with a hybrid strategy using Unicycler software. We found that the mitochondrial genome comprised two circular chromosomes with lengths of 867,678 bp and 153,529 bp, encoding 40 protein-coding genes, 26 tRNA genes, and three rRNA genes. We also detected 270 Simple Sequence Repeats and 34 tandem repeats in the mitochondrial genome. We found 515 high-scoring sequence pairs (HSPs) for a self-to-self similarity comparison using BLASTn. Three HSPs were found to mediate recombination by the mapping of long reads. Furthermore, we predicted 472 using deep-mt with the convolutional neural network model. Then we randomly validated 90 RNA editing events by PCR amplification and Sanger sequencing, with the majority being non-synonymous substitutions and only three being synonymous substitutions. These findings provide valuable insights into the genetic characteristics of the C. arabica mitochondrial genome, which can be helpful for future study on coffee breeding and mitochondrial genome evolution.

Conclusion

Our study sheds new light on the evolution of C. arabica organelle genomes and their potential use in genetic breeding, providing valuable data for developing molecular markers that can improve crop productivity and quality. Furthermore, the discovery of RNA editing events in the mitochondrial genome of C. arabica offers insights into the regulation of gene expression in this species, contributing to a better understanding of coffee genetics and evolution.

Defective kernel 66 encodes a GTPase essential for kernel development in maize

The mitochondrion is a semi-autonomous organelle that provides energy for cell activities through oxidative phosphorylation. In this study, we identified a defective kernel 66 (dek66)-mutant maize with defective kernels. We characterized a candidate gene, DEK66, encoding a ribosomal assembly factor located in mitochondria and possessing GTPase activity (which belongs to the ribosome biogenesis GTPase A family). In the dek66 mutant, impairment of mitochondrial structure and function led to the accumulation of reactive oxygen species and promoted programmed cell death in endosperm cells. Furthermore, the transcript levels of most of the key genes associated with nutrient storage, mitochondrial respiratory chain complex, and mitochondrial ribosomes in the dek66 mutant were significantly altered. Collectively, the results suggest that DEK66 is essential for the development of maize kernels by affecting mitochondrial function. This study provides a reference for understanding the impact of a mitochondrial ribosomal assembly factor in maize kernel development.

Comparative Analysis of Tylosema esculentum Mitochondrial DNA Revealed Two Distinct Genome Structures

Tylosema esculentum, commonly known as the marama bean, is an underutilized legume with nutritious seeds, holding potential to enhance food security in southern Africa due to its resilience to prolonged drought and heat. To promote the selection of this agronomically valuable germplasm, this study assembled and compared the mitogenomes of 84 marama individuals, identifying variations in genome structure, single-nucleotide polymorphisms (SNPs), insertions/deletions (indels), heteroplasmy, and horizontal transfer. Two distinct germplasms were identified, and a novel mitogenome structure consisting of three circular molecules and one long linear chromosome was discovered. The structural variation led to an increased copy number of specific genes, nad5, nad9, rrnS, rrn5, trnC, and trnfM. The two mitogenomes also exhibited differences at 230 loci, with only one notable nonsynonymous substitution in the matR gene. Heteroplasmy was concentrated at certain loci on chromosome LS1 (OK638188). Moreover, the marama mitogenome contained an over 9 kb insertion of cpDNA, originating from chloroplast genomes, but had accumulated mutations and lost gene functionality. The evolutionary and comparative genomics analysis indicated that mitogenome divergence in marama might not be solely constrained by geographical factors. Additionally, marama, as a member from the Cercidoideae subfamily, tends to possess a more complete set of mitochondrial genes than Faboideae legumes.

The Mitochondrial Genome of the Holoparasitic Plant Thonningia sanguinea Provides Insights into the Evolution of the Multichromosomal Structure

Multichromosomal mitochondrial genome (mitogenome) structures have repeatedly evolved in many lineages of angiosperms. However, the underlying mechanism remains unclear. The mitogenomes of three genera of Balanophoraceae, namely Lophophytum, Ombrophytum, and Rhopalocnemis, have already been sequenced and assembled, all showing a highly multichromosomal structure, albeit with different genome and chromosome sizes. It is expected that characterization of additional lineages of this family may expand the knowledge of mitogenome diversity and provide insights into the evolution of the plant mitogenome structure and size. Here, we assembled and characterized the mitogenome of Thonningia sanguinea, which, together with Balanophora, forms a clade sister to the clade comprising Lophophytum, Ombrophytum, and Rhopalocnemis. The mitogenome of T. sanguinea possesses a multichromosomal structure of 18 circular chromosomes of 8.7-19.2 kb, with a total size of 246,247 bp. There are very limited shared regions and poor chromosomal correspondence between T. sanguinea and other Balanophoraceae species, suggesting frequent rearrangements and rapid sequence turnover. Numerous medium- and small-sized repeats were identified in the T. sanguinea mitogenome; however, no repeat-mediated recombination was detected, which was verified by Illumina reads mapping and PCR experiments. Intraspecific mitogenome variations in T. sanguinea are mostly insertions and deletions, some of which can lead to degradation of perfect repeats in one or two accessions. Based on the mitogenome features of T. sanguinea, we propose a mechanism to explain the evolution of a multichromosomal mitogenome from a master circle, which involves mutation in organellar DNA replication, recombination and repair genes, decrease of recombination, and repeat degradation.

Structural and gene composition variation of the complete mitochondrial genome of Mammillaria huitzilopochtli (Cactaceae, Caryophyllales), revealed by de novo assembly

BACKGROUND

Structural descriptions of complete genomes have elucidated evolutionary processes in angiosperms. In Cactaceae (Caryophyllales), a high structural diversity of the chloroplast genome has been identified within and among genera. In this study, we assembled the first mitochondrial genome (mtDNA) for the short-globose cactus Mammillaria huitzilopochtli. For comparative purposes, we used the published genomes of 19 different angiosperms and the gymnosperm Cycas taitungensis as an external group for phylogenetic issues.

RESULTS

The mtDNA of M. huitzilopochtli was assembled into one linear chromosome of 2,052,004 bp, in which 65 genes were annotated. These genes account for 57,606 bp including 34 protein-coding genes (PCGs), 27 tRNAs, and three rRNAs. In the non-coding sequences, repeats were abundant, with a total of 4,550 (179,215 bp). In addition, five complete genes (psaC and four tRNAs) of chloroplast origin were documented. Negative selection was estimated for most (23) of the PCGs. The phylogenetic tree showed a topology consistent with previous analyses based on the chloroplast genome.

CONCLUSIONS

The number and type of genes contained in the mtDNA of M. huitzilopochtli were similar to those reported in 19 other angiosperm species, regardless of their phylogenetic relationships. Although other Caryophyllids exhibit strong differences in structural arrangement and total size of mtDNA, these differences do not result in an increase in the typical number and types of genes found in M. huitzilopochtli. We concluded that the total size of mtDNA in angiosperms increases by the lengthening of the non-coding sequences rather than a significant gain of coding genes.

Complete mitochondrial genome of Agrostis stolonifera: insights into structure, Codon usage, repeats, and RNA editing

BACKGROUND

Plants possess mitochondrial genomes that are large and complex compared to animals. Despite their size, plant mitochondrial genomes do not contain significantly more genes than their animal counterparts. Studies into the sequence and structure of plant mitochondrial genomes heavily imply that the main mechanism driving replication of plant mtDNA, and offer valuable insights into plant evolution, energy production, and environmental adaptation.

RESULTS

This study presents the first comprehensive analysis of Agrostis stolonifera's mitochondrial genome, characterized by a branched structure comprising three contiguous chromosomes, totaling 560,800 bp with a GC content of 44.07%. Annotations reveal 33 unique protein-coding genes (PCGs), 19 tRNA genes, and 3 rRNA genes. The predominant codons for alanine and glutamine are GCU and CAA, respectively, while cysteine and phenylalanine exhibit weaker codon usage biases. The mitogenome contains 73, 34, and 23 simple sequence repeats (SSRs) on chromosomes 1, 2, and 3, respectively. Chromosome 1 exhibits the most frequent A-repeat monomeric SSR, whereas chromosome 2 displays the most common U-repeat monomeric SSR. DNA transformation analysis identifies 48 homologous fragments between the mitogenome and chloroplast genome, representing 3.41% of the mitogenome's total length. The PREP suite detects 460 C-U RNA editing events across 33 mitochondrial PCGs, with the highest count in the ccmFn gene and the lowest in the rps7 gene. Phylogenetic analysis confirms A. stolonifera's placement within the Pooideae subfamily, showing a close relationship to Lolium perenne, consistent with the APG IV classification system. Numerous homologous co-linear blocks are observed in A. stolonifera's mitogenomes and those of related species, while certain regions lack homology.

CONCLUSIONS

The unique features and complexities of the A. stolonifera mitochondrial genome, along with its similarities and differences to related species, provide valuable insights into plant evolution, energy production, and environmental adaptation. The findings from this study significantly contribute to the growing body of knowledge on plant mitochondrial genomes and their role in plant biology.

The translocase of the inner mitochondrial membrane 22-2 is required for mitochondrial membrane function during Arabidopsis seed development

The carrier translocase (also known as translocase of the inner membrane 22; TIM22 complex) is an important component of the mitochondrial protein import apparatus. However, the biological functions of AtTIM22-2 in Arabidopsis remain poorly defined. Here, we report studies on two tim22-2 mutants that exhibit defects in embryo and endosperm development, leading to seed abortion. AtTIM22-2, which was localized in mitochondria, was widely expressed in embryos and in various seedling organs. Loss of AtTIM22-2 function resulted in irregular mitochondrial cristae, decreased respiratory activity, and a lower membrane potential, together with changes in gene expression and enzyme activity related to reactive oxygen species (ROS) metabolism, leading to increased accumulation of ROS in the embryo. The levels of transcripts encoding mitochondrial protein import components were also altered in the tim22-2 mutants. Furthermore, mass spectrometry, bimolecular fluorescence complementation and co-immunoprecipitation assays revealed that AtTIM22-2 interacted with AtTIM23-2, AtB14.7 (a member of Arabidopsis OEP16 family encoded by At2G42210), and AT5G27395 (mitochondrial inner membrane translocase complex, subunit TIM44-related protein). Taken together, these results demonstrate that AtTIM22-2 is essential for maintaining mitochondrial membrane functions during seed development. These findings lay the foundations for a new model of the composition and functions of the TIM22 complex in higher plants.

Assembly and analysis of the mitochondrial genome of Prunella vulgaris

Prunella vulgaris (Lamiaceae) is widely distributed in Eurasia. Former studies have demonstrated that P. vulgaris has a wide range of pharmacological effects. Nevertheless, no complete P. vulgaris mitochondrial genome has been reported, which limits further understanding of the biology of P. vulgaris. Here, we assembled the first complete mitochondrial genome of P. vulgaris using a hybrid assembly strategy based on sequencing data from both Nanopore and Illumina platforms. Then, the mitochondrial genome of P. vulgaris was analyzed comprehensively in terms of gene content, codon preference, intercellular gene transfer, phylogeny, and RNA editing. The mitochondrial genome of P. vulgaris has two circular structures. It has a total length of 297, 777 bp, a GC content of 43.92%, and 29 unique protein-coding genes (PCGs). There are 76 simple sequence repeats (SSRs) in the mitochondrial genome, of which tetrameric accounts for a large percentage (43.4%). A comparative analysis between the mitochondrial and chloroplast genomes revealed that 36 homologous fragments exist in them, with a total length of 28, 895 bp. The phylogenetic analysis showed that P. vulgaris belongs to the Lamiales family Lamiaceae and P. vulgaris is closely related to Salvia miltiorrhiza. In addition, the mitochondrial genome sequences of seven species of Lamiaceae are unconservative in their alignments and undergo frequent genome reorganization. This work reports for the first time the complete mitochondrial genome of P. vulgaris, which provides useful genetic information for further Prunella studies.

Mitochondrial Genome Diversity across the Subphylum Saccharomycotina

Eukaryotic life depends on the functional elements encoded by both the nuclear genome and organellar genomes, such as those contained within the mitochondria. The content, size, and structure of the mitochondrial genome varies across organisms with potentially large implications for phenotypic variance and resulting evolutionary trajectories. Among yeasts in the subphylum Saccharomycotina, extensive differences have been observed in various species relative to the model yeast Saccharomyces cerevisiae, but mitochondrial genome sampling across many groups has been scarce, even as hundreds of nuclear genomes have become available. By extracting mitochondrial assemblies from existing short-read genome sequence datasets, we have greatly expanded both the number of available genomes and the coverage across sparsely sampled clades. Comparison of 353 yeast mitochondrial genomes revealed that, while size and GC content were fairly consistent across species, those in the genera Metschnikowia and Saccharomyces trended larger, while several species in the order Saccharomycetales, which includes S. cerevisiae, exhibited lower GC content. Extreme examples for both size and GC content were scattered throughout the subphylum. All mitochondrial genomes shared a core set of protein-coding genes for Complexes III, IV, and V, but they varied in the presence or absence of mitochondrially-encoded canonical Complex I genes. We traced the loss of Complex I genes to a major event in the ancestor of the orders Saccharomycetales and Saccharomycodales, but we also observed several independent losses in the orders Phaffomycetales, Pichiales, and Dipodascales. In contrast to prior hypotheses based on smaller-scale datasets, comparison of evolutionary rates in protein-coding genes showed no bias towards elevated rates among aerobically fermenting (Crabtree/Warburg-positive) yeasts. Mitochondrial introns were widely distributed, but they were highly enriched in some groups. The majority of mitochondrial introns were poorly conserved within groups, but several were shared within groups, between groups, and even across taxonomic orders, which is consistent with horizontal gene transfer, likely involving homing endonucleases acting as selfish elements. As the number of available fungal nuclear genomes continues to expand, the methods described here to retrieve mitochondrial genome sequences from these datasets will prove invaluable to ensuring that studies of fungal mitochondrial genomes keep pace with their nuclear counterparts.

The first complete mitochondrial genome of Carex (C. breviculmis): a significantly expanded genome with highly structural variations

MAIN CONCLUSION

The first complete mitochondrial genome of Carex (C. breviculmis) was sequenced and assembled, and its genomic signature was analyzed and the possible conformations of its mitochondrial genome were validated. Carex breviculmis is a very adaptable grass that is highly resistant to environmental stresses such as drought and low light. It is also admired as a landscape plant with high development prospects and scientific research value. In this study, the mitochondrial genome of C. breviculmis was assembled using Pacbio and Illumina sequencing data. We detected 267 pairs of repeats and found that three pairs of repeats could mediate the recombination of its mitochondrial genome and formed four possible conformations, of which we verified the two conformations mediated by the shortest pair of repeats using PCR amplification and Sanger sequencing. The major conformation of the C. breviculmis mitochondrial genome is a 1,414,795 bp long circular molecule with 33 annotated protein-coding genes, 15 tRNA genes, and three rRNA genes. We detected a total of 25 homologous sequences between the chloroplast and mitochondrial genomes, corresponding to 0.40% of the mitochondrial genome. Combined with the low GC content (41.24%), we conclude that the reduction in RNA editing sites in the C. breviculmis mitochondrial genome may be due to an accumulation of point mutations in C-to-T or retroprocessing events within the genome. The relatively low number of RNA editing sites in its mitochondrial genome could serve as important material for subsequent studies on the selection pressure of RNA editing in angiosperms. A maximum likelihood analysis based on 23 conserved mitochondrial genes from 28 species reflects an accurate evolutionary and taxonomic position of C. breviculmis. This research provided us with a comprehensive understanding of the mitochondrial genome of Carex and also provided important information for its molecular breeding.

Comparative analysis of mitochondrial genomes of Schisandra repanda and Kadsura japonica

The family Schisandraceae is a basal angiosperm plant group distributed in East and Southeast Asia and includes many medicinal plant species such as Schisandra chinensis. In this study, mitochondrial genomes (mitogenomes) of two species, Schisandra repanda and Kadsura japonica, in the family were characterized through de novo assembly using sequencing data obtained with Oxford Nanopore and Illumina sequencing technologies. The mitogenomes of S. repanda were assembled into one circular contig (571,107 bp) and four linear contigs (10,898-607,430 bp), with a total of 60 genes: 38 protein-coding genes (PCGs), 19 tRNA genes, and 3 rRNA genes. The mitogenomes of K. japonica were assembled into five circular contigs (211,474-973,503 bp) and three linear contigs (8,010-72,712 bp), with a total of 66 genes: 44 PCGs, 19 tRNA genes, and 3 rRNA genes. The mitogenomes of the two species had complex structural features with high repeat numbers and chloroplast-derived sequences, as observed in other plant mitogenomes. Phylogenetic analysis based on PCGs revealed the taxonomical relationships of S. repanda and K. japonica with other species from Schisandraceae. Finally, molecular markers were developed to distinguish between S. repanda, K. japonica, and S. chinensis on the basis of InDel polymorphisms present in the mitogenomes. The mitogenomes of S. repanda and K. japonica will be valuable resources for molecular and taxonomic studies of plant species that belong to the family Schisandraceae.

The complete mitochondrial genome of Amorphophallus albus and development of molecular markers for five Amorphophallus species based on mitochondrial DNA

Introduction

Amorphophallus albus is an herbaceous, cormous, perennial plant used as a food source and traditional medicine in Asia.

Methods

In this study, we assembled and annotated the complete mitochondrial genome (mitogenome) of A. albus. Then we analyzed the repeated elements and mitochondrial plastid sequences (MTPTs), predicted RNA editing sites in mitochondrial protein-coding genes (PCGs). Lastly, we inferred the phylogenetic relationships of A. albus and other angiosperms based on mitochondrial PCGs, and designed two molecular markers based on mitochondrial DNA.

Results and discussion

The complete mitogenome of A. albus consists of 19 circular chromosomes. And the total length of A. albus mitogenome is 537,044 bp, with the longest chromosome measuring 56,458 bp and the shortest measuring 12,040 bp. We identified and annotated a total of 36 protein-coding genes (PCGs), 21 tRNA genes, and 3 rRNA genes in the mitogenome. Additionally, we analyzed mitochondrial plastid DNAs (MTPTs) and identified 20 MTPTs between the two organelle genomes, with a combined length of 22,421 bp, accounting for 12.76% of the plastome. Besides, we predicted a total of 676 C to U RNA editing sites on 36 protein-coding genes of high confidence using Deepred-mt. Furthermore, extensive genomic rearrangement was observed between A. albus and the related mitogenomes. We conducted phylogenetic analyses based on mitochondrial PCGs to determine the evolutionary relationships between A. albus and other angiosperms. Finally, we developed and validated two molecular markers, Ai156 and Ai976, based on two intron regions (nad2i156 and nad4i976) respectively. The discrimination success rate was 100 % in validation experiments for five widely grown konjac species. Our results reveal the multi-chromosome mitogenome of A. albus, and the developed markers will facilitate molecular identification of this genus.

Mitogenomic Research of Silverleaf Sunflower (Helianthus argophyllus) and Its Interspecific Hybrids

Interspecific hybridization is widespread for sunflowers, both in wild populations and commercial breeding. One of the most common species that can efficiently cross with Helianthus annuus is the Silverleaf sunflower-Helianthus argophyllus. The current study carried out structural and functional organization analyses of mitochondrial DNA in H. argophyllus and the interspecific hybrid, H. annuus (VIR114A line) × H. argophyllus. The complete mitogenome of H. argophyllus counts 300,843 bp, has a similar organization to the mitogenome of cultivated sunflower, and holds SNPs typical for wild sunflowers. RNA editing analysis predicted 484 sites in H. argophyllus mitochondrial CDS. The mitochondrial genome of the H. annuus × H. argophyllus hybrid is identical to the maternal line (VIR114A). We expected that significant rearrangements in the mitochondrial DNA of the hybrid would occur, due to the frequent recombination. However, the hybrid mitogenome lacks rearrangements, presumably due to the preservation of nuclear-cytoplasmic interaction paths.

Assembly and Comparative Analysis of the Complete Mitochondrial Genome of Two Species of Calla Lilies (Zantedeschia, Araceae)

In this study, the mitochondrial genomes of two calla species, Zantedeschia aethiopica Spreng. and Zantedeschia odorata Perry., were assembled and compared for the first time. The Z. aethiopica mt genome was assembled into a single circular chromosome, measuring 675,575 bp in length with a 45.85% GC content. In contrast, the Z. odorata mt genome consisted of bicyclic chromosomes (chromosomes 1 and 2), measuring 719,764 bp and exhibiting a 45.79% GC content. Both mitogenomes harbored similar gene compositions, with 56 and 58 genes identified in Z. aethiopica and Z. odorata, respectively. Analyses of codon usage, sequence repeats, gene migration from chloroplast to mitochondrial, and RNA editing were conducted for both Z. aethiopica and Z. odorata mt genomes. Phylogenetic examination based on the mt genomes of these two species and 30 other taxa provided insights into their evolutionary relationships. Additionally, the core genes in the gynoecium, stamens, and mature pollen grains of the Z. aethiopica mt genome were investigated, which revealed maternal mitochondrial inheritance in this species. In summary, this study offers valuable genomic resources for future research on mitogenome evolution and the molecular breeding of calla lily.

The organellar genomes of Pellidae (Marchantiophyta): the evidence of cryptic speciation, conflicting phylogenies and extraordinary reduction of mitogenomes in simple thalloid liverwort lineage

Organellar genomes of liverworts are considered as one of the most stable among plants, with rare events of gene loss and structural rearrangements. However, not all lineages of liverworts are equally explored in the field of organellar genomics, and subclass Pellidae is one of the less known. Hybrid assembly, using both short- and long-read technologies enabled the assembly of repeat-rich mitogenomes of Pellia and Apopellia revealing extraordinary reduction of length in the latter which impacts only intergenic spacers. The mitogenomes of Apopellia were revealed to be the smallest among all known liverworts-109 k bp, despite retaining all introns. The study also showed the loss of one tRNA gene in Apopellia mitogenome, although it had no impact on the codon usage pattern of mitochondrial protein coding genes. Moreover, it was revealed that Apopellia and Pellia differ in codon usage by plastome CDSs, despite identical tRNA gene content. Molecular identification of species is especially important where traditional taxonomic methods fail, especially within Pellidae where cryptic speciation is well recognized. The simple morphology of these species and a tendency towards environmental plasticity make them complicated in identification. Application of super-barcodes, based on complete mitochondrial or plastid genomes sequences enable identification of all cryptic lineages within Apopellia and Pellia genera, however in some particular cases, mitogenomes were more efficient in species delimitation than plastomes.

Unveiling the Mysteries of Non-Mendelian Heredity in Plant Breeding

Mendelian heredity is the cornerstone of plant breeding and has been used to develop new varieties of plants since the 19th century. However, there are several breeding cases, such as cytoplasmic inheritance, methylation, epigenetics, hybrid vigor, and loss of heterozygosity (LOH), where Mendelian heredity is not applicable, known as non-Mendelian heredity. This type of inheritance can be influenced by several factors besides the genetic architecture of the plant and its breeding potential. Therefore, exploring various non-Mendelian heredity mechanisms, their prevalence in plants, and the implications for plant breeding is of paramount importance to accelerate the pace of crop improvement. In this review, we examine the current understanding of non-Mendelian heredity in plants, including the mechanisms, inheritance patterns, and applications in plant breeding, provide an overview of the various forms of non-Mendelian inheritance (including epigenetic inheritance, cytoplasmic inheritance, hybrid vigor, and LOH), explore insight into the implications of non-Mendelian heredity in plant breeding, and the potential it holds for future research.

Assembly of the Complete Mitochondrial Genome of Pereskia aculeata Revealed That Two Pairs of Repetitive Elements Mediated the Recombination of the Genome

Pereskia aculeata is a potential new crop species that has both food and medicinal (antinociceptive activity) properties. However, comprehensive genomic research on P. aculeata is still lacking, particularly concerning its organelle genome. In this study, P. aculeata was studied to sequence the mitochondrial genome (mitogenome) and to ascertain the assembly, informational content, and developmental expression of the mitogenome. The findings revealed that the mitogenome of P. aculeata is circular and measures 515,187 bp in length with a GC content of 44.05%. It contains 52 unique genes, including 33 protein-coding genes, 19 tRNA genes, and three rRNA genes. Additionally, the mitogenome analysis identified 165 SSRs, primarily consisting of tetra-nucleotides, and 421 pairs of dispersed repeats with lengths greater than or equal to 30, which were mainly forward repeats. Based on long reads and PCR experiments, we confirmed that two pairs of long-fragment repetitive elements were highly involved with the mitogenome recombination process. Furthermore, there were 38 homologous fragments detected between the mitogenome and chloroplast genome, and the longest fragment was 3962 bp. This is the first report on the mitogenome in the family Cactaceae. The decoding of the mitogenome of P. aculeata will provide important genetic materials for phylogenetic studies of Cactaceae and promote the utilization of species germplasm resources.

Identification, cloning and characterization of AcMSH1 from Onion (Allium cepa L.)

BACKGROUND

MSH1 (MutS homolog1) is a nuclear-encoded protein that plays a crucial role in maintaining low mutation rates and stability of the organellar genome. While plastid MSH1 maintains nuclear epigenome plasticity and affects plant development patterns, mitochondrial MSH1 suppresses illegitimate recombination within the mitochondrial genome, affects mitochondrial genome substoichiometric shifting activity and induces cytoplasmic male sterility (CMS) in crops. However, a detailed functional investigation of onion MSH1 has yet to be achieved.

MATERIALS AND RESULTS

The homology analysis of onion genome database identified a single copy of the AcMSH1 gene in the onion cv. Bhima Super. In silico analysis of AcMSH1 protein sequence revealed the presence of 6 conserved functional domains including a unique MSH1-specific GIY-YIG endonuclease domain at the C-terminal end. At N-terminal end, it has signal peptide sequences targeting chloroplast and mitochondria. The concentration of AcMSH1 was found to be highest in isolated mitochondria, followed by chloroplasts, and negligible in the cytoplasmic fraction; which proved its localization to the mitochondria and chloroplasts. Quantitative expression analysis revealed that AcMSH1 protein levels were highest in leaves, followed by flower buds, root tips, flowers, and umbels, with the lowest amount found in callus tissue.

CONCLUSION

Onion genome has single copy of MSH1, with characteristic GIY-YIG endonuclease domain. AcMSH1 targeted towards both chloroplasts and mitochondria. The identification and characterisation of AcMSH1 may provide valuable insights into the development of CMS lines in onion.

Complete Mitogenome and Phylogenetic Analysis of the Carthamus tinctorius L

Carthamus tinctorius L. 1753 (Asteraceae), also called safflower, is a cash crop with both edible and medical properties. We analyzed and reported the safflower mitogenome based on combined short and long reads obtained from Illumina and Pacbio platforms, respectively. This safflower mitogenome mainly contained two circular chromosomes, with a total length of 321,872 bp, and encoded 55 unique genes, including 34 protein-coding genes (PCGs), 3 rRNA genes, and 18 tRNA genes. The total length of repeat sequences greater than 30 bp was 24,953 bp, accounting for 7.75% of the whole mitogenome. Furthermore, we characterized the RNA editing sites of protein-coding genes located in the safflower mitogenome, and the total number of RNA editing sites was 504. Then, we revealed partial sequence transfer events between plastid and mitochondria, in which one plastid-derived gene (psaB) remained intact in the mitogenome. Despite extensive arrangement events among the three mitogenomes of C. tinctorius, Arctium lappa, and Saussurea costus, the constructed phylogenetic tree based on mitogenome PCGs showed that C. tinctorius has a closer relationship with three Cardueae species, A. lappa, A. tomentosum, and S. costus, which is similar to the phylogeny constructed from the PCGs of plastid genomes. This mitogenome not only enriches the genetic information of safflower but also will be useful in the phylogeny and evolution study of the Asteraceae.

Understanding parasitism in Loranthaceae: Insights from plastome and mitogenome of Helicanthes elastica

Loranthaceae is the largest family of the order Santalales and includes root and stem hemiparasites. The parasites are known to exhibit reductions in the genomic features as well as relaxed or intensified selection shifts. In this study, we report plastome and mitogenome sequence of Helicanthes elastica (subtribe Amyeminae, tribe Lorantheae), an endemic, monotypic genus of Western Ghats, India growing on remarkably diverse host range. The length of plastome sequence was 1,28,805 bp while that of mitogenome was 1,65,273 bp. This is the smallest mitogenome from Loranthaceae reported till date. The plastome of Helicanthes exhibited loss of ndh genes (ψndhB), ψinfA, rps15, rps16, rpl32, trnK-UUU, trnG-UCC, trnV-UAC and trnA-UGC while mitogenome exhibited pseudogenized cox2, nad1 and nad4 genes. The comparative study of Loranthaceae plastomes revealed that the pseudogenization or loss of genes was not specific to any genus or tribe and variation was noted in the number of introns of clpP gene in the family. Several photosynthetic genes have undergone relaxed selection supporting lower photosynthetic rates in parasitic plants while some respiratory genes exhibited intensified selection supporting the idea of host-parasite arm race in Loranthaceae. The plastome gene content was found conserved in root hemiparasites compared to stem hemiparasites. The atp1 gene of mitogenome was chimeric and part of it exhibited similarities with Lamiales members. The phylogenetic analysis based on plastid genes placed Helicanthes sister to the members of subtribe Dendrophthoinae.

The Evolution of Mitochondrial Genomes between Two Cymbidium Sister Species: Dozens of Circular Chromosomes and the Maintenance and Deterioration of Genome Synteny

Plant mitochondrial genomes (mitogenomes) exhibit fluid genome architectures, which could lead to the rapid erosion of genome synteny over a short evolutionary time scale. Among the species-rich orchid family, the leafy Cymbidium lancifolium and leafless Cymbidium macrorhizon are sister species with remarkable differences in morphology and nutritional physiology. Although our understanding of the evolution of mitochondria is incomplete, these sister taxa are ideal for examining this subject. In this study, the complete mitogenomes of C. lancifolium and C. macrorhizon, totaling 704,244 bp and 650,751 bp, respectively, were assembled. In the 2 mitogenomes, 38 protein-coding genes, 18 cis- and 6 trans-spliced introns, and approximately 611 Kb of homologous sequences are identical; overall, they have 99.4% genome-wide similarity. Slight variations in the mitogenomes of C. lancifolium and C. macrorhizon in repeat content (21.0 Kb and 21.6 Kb, respectively) and mitochondrial DNA of plastid origin (MIPT; 38.2 Kb and 37.5 Kb, respectively) were observed. The mitogenome architectures of C. lancifolium and C. macrorhizon are complex and comprise 23 and 22 mini-circular chromosomes, respectively. Pairwise comparisons indicate that the two mitogenomes are largely syntenic, and the disparity in chromosome numbers is likely due to repeat-mediated rearrangements among different chromosomes. Notably, approximately 93.2 Kb C. lancifolium mitochondrial sequences lack any homology in the C. macrorhizon mitogenome, indicating frequent DNA gains and losses, which accounts mainly for the size variation. Our findings provide unique insights into mitogenome evolution in leafy and leafless plants of sister species and shed light on mitogenome dynamics during the transition from mixotrophy to mycoheterotrophy.