Comparative Analysis of Chloroplast Genomes for the Genus Manglietia Blume (Magnoliaceae): Molecular Structure and Phylogenetic Evolution

Manglietia Blume, belonging to the Magnoliaceae family and mainly distributed in tropical and subtropical regions of Asia, has great scientific and economic value. In this study, we employed next-generation sequencing followed by de novo assembly to investigate the adaptive evolution of Manglietia using plastid genetic information. We newly sequenced the complete or nearly complete plastomes of four Manglietia species (Manglietia aromatica, Manglietia calcarea, Manglietia kwangtungensis, and Manglietia glauca) and conducted comparative analysis with seventeen published plastomes to examine the evolutionary pattern within this genus. The plastomes of these five newly sequenced Manglietia species range from 157,093 bp (M. calcarea2) to 160,493 bp (M. kwangtungensis), all exhibiting circular structures when mapped. Nucleotide diversity was observed across the plastomes, leading us to identify 13 mutational hotspot regions, comprising eight intergenic spacer regions and five gene regions. Our phylogenetic analyses based on 77 protein-coding genes generated phylogenetic relationships with high support and resolution for Manglietia. This genus can be divided into three clades, and the previously proposed infrageneric classifications are not supported by our studies. Furthermore, the close affinity between M. aromatica and M. calcarea is supported by the present work, and further studies are necessary to conclude the taxonomic treatment for the latter. These results provide resources for the comparative plastome, breeding, and plastid genetic engineering of Magnoliaceae and flowering plants.

Transcriptome data analysis provides insights into the conservation of Michelia lacei, a plant species with extremely small populations distributed in Yunnan province, China

BACKGROUND

Michelia lacei W.W.Smith (Magnoliaceae), was classified as a Plant Species with Extremely Small Populations (PSESP) by the Yunnan Provincial Government in both action plans of 2012 and 2021. This evergreen tree is known for its high ornamental and scientific value, but it faces significant threats due to its extremely small population size and narrow geographical distribution. The study aims to understand the genetic structure, diversity, and demographic history of this species to inform its conservation strategies.

RESULTS

The analysis of transcriptome data from 64 individuals across seven populations of M. lacei identified three distinct genetic clusters and generated 104,616 single-nucleotide polymorphisms (SNPs). The KM ex-situ population, originating from Longling County, exhibited unique genetic features, suggesting limited gene flow. The genetic diversity was substantial, with significant differences between populations, particularly between the KM lineage and the OTHER lineage. Demographic history inferred from the data indicated population experienced three significant population declines during glaciations, followed by periods of recovery. We estimated the effective population size (Ne) of the KM and OTHER lineages 1,000 years ago were 85,851 and 416,622, respectively. Gene flow analysis suggested past gene flow between populations, but the KM ex-situ population showed no recent gene flow. A total of 805 outlier SNPs, associated with four environmental factors, suggest potential local adaptation and showcase the species' adaptive potential. Particularly, the BZ displayed 515 adaptive loci, highlighting its strong potential for adaptation within this group.

CONCLUSIONS

The comprehensive genomic analysis of M. lacei provides valuable insights into its genetic background and highlights the urgent need for conservation efforts. The study underscores the importance of ex-situ conservation methods, such as seed collection and vegetative propagation, to safeguard genetic diversity and promote population restoration. The preservation of populations like MC and BZ is crucial for maintaining the species' genetic diversity. In-situ conservation measures, including the establishment of in-situ conservation sites and community engagement, are essential to enhance protection awareness and ensure the long-term survival of this threatened plant species.

Transcriptome and metabolome analyses reveal novel insights into the seed germination of Michelia chapensis, an endangered species in China

Michelia chapensis Dandy, a well-known medicinal woody plant endemic to China, is endangered and seriously constricted by seed dormancy-induced low-regeneration in natural conditions. Cold stratification can effectively reduce seed dormancy and promote the seed germination of M. chapensis. However, the molecular events and systematic changes that occurred during seed germination in M. chapensis remain largely unknown. In this study, we carried out transcriptomic and metabolomic analyses to elucidate the potential molecular mechanisms underlying seed germination in M. chapensis under cold stratification. The results showed that the embryo cells became bigger and looser with increasing stratification time. Moreover, the endosperm appeared reduced due to the consumption of nutrients. Seventeen phytohormones were examined by the metabolome targeted for hormones. Compared with the ES (no stratification), the levels of indole-3-acetic acid (IAA) and gibberellin A₃ (GA₃) were increased in the MS (stratification for 45 days), while the abscisic acid (ABA) was downregulated in both MS and LS (stratification for 90 days). The transcriptome profiling identified 24975 differentially expressed genes (DEGs) in the seeds during germination. The seed germination of M. chapensis was mainly regulated by the biological pathways of plant hormone signal transduction, energy supply, secondary metabolite biosynthesis, photosynthesis-related metabolism, and transcriptional regulation. This study reveals the biological evidence of seed germination at the transcriptional level and provides a foundation for unraveling molecular mechanisms regulating the seed germination of M. chapensis.

The Chimonanthus salicifolius genome provides insight into magnoliid evolution and flavonoid biosynthesis

Chimonanthus salicifolius, a member of the Calycanthaceae of magnoliids, is one of the most famous medicinal plants in Eastern China. Here, we report a chromosome-level genome assembly of C. salicifolius, comprising 820.1 Mb of genomic sequence with a contig N50 of 2.3 Mb and containing 36 651 annotated protein-coding genes. Phylogenetic analyses revealed that magnoliids were sister to the eudicots. Two rounds of ancient whole-genome duplication were inferred in the C. salicifolious genome. One is shared by Calycanthaceae after its divergence with Lauraceae, and the other is in the ancestry of Magnoliales and Laurales. Notably, long genes with > 20 kb in length were much more prevalent in the magnoliid genomes compared with other angiosperms, which could be caused by the length expansion of introns inserted by transposon elements. Homologous genes within the flavonoid pathway for C. salicifolius were identified, and correlation of the gene expression and the contents of flavonoid metabolites revealed potential critical genes involved in flavonoids biosynthesis. This study not only provides an additional whole-genome sequence from the magnoliids, but also opens the door to functional genomic research and molecular breeding of C. salicifolius.

Development of cryopreservation for Loxocarya cinerea---an endemic Australian plant species important for post-mining restoration

We report the development of a cryopreservation protocol for the endemic Western Australian plant species Loxocarya cinerea (Restionaceae). Shoot tips from two genotypes, SXH404 and SXH804, were cryopreserved using the droplet-vitrification technique. Control explants, which were cryoprotected, but not cooled, showed regeneration for both genotypes (SXH404, 22.1 +/- 5.9%; SXH804, 67.7 +/- 9.6%). Extension of incubation in PVS2 from 30 to 60 min did not lead to survival after cryopreservation. Thermal analysis using differential scanning calorimetry confirmed the beneficial effect of a loading phase but also revealed no or very little ice formation after cryoprotection of shoot tips in other treatments. Regeneration following cryopreservation was obtained for genotype SXH804 (4.3 +/- 2.1%) but not for SXH404. Regenerated explants of L. cinerea SXH804 were morphologically identical to tissue-cultured plants. As an alternative to shoot tips, callus tissues of clone SXH404 were successfully cryopreserved (> 66.7% post LN survival) using the same protocol.

Complete chloroplast genome sequence of Magnolia grandiflora and comparative analysis with related species

Magnolia grandiflora is an important medicinal, ornamental and horticultural plant species. The chloroplast (cp) genome of M. grandiflora was sequenced using a 454 sequencing platform and the genome structure was compared with other related species. The complete cp genome of M. grandiflora was 159623 bp in length and contained a pair of inverted repeats (IR) of 26563 bp separated by large and small single copy (LSC, SSC) regions of 87757 and 18740 bp, respectively. A total of 129 genes were successfully annotated, 18 of which included introns. The identity, number and GC content of M. grandiflora cp genes were similar to those of other Magnoliaceae species genomes. Analysis revealed 218 simple sequence repeat (SSR) loci, most composed of A or T, contributing to a bias in base composition. The types and abundances of repeat units in Magnoliaceae species were relatively conserved and these loci will be useful for developing M. grandiflora cp genome vectors. In addition, results indicated that the cp genome size in Magnoliaceae species and the position of the IR border were closely related to the length of the ycf1 gene. Phylogenetic analyses based on 66 shared genes from 30 species using maximum parsimony (MP) and maximum likelihood (ML) methods provided strong support for the phylogenetic position of Magnolia. The availability of the complete cp genome sequence of M. grandiflora provides valuable information for breeding of desirable varieties, cp genetic engineering, developing useful molecular markers and phylogenetic analyses in Magnoliaceae.

Isolation and characterization of microsatellite loci in Tsoongiodendron odorum (Magnoliaceae)

PREMISE OF THE STUDY

Microsatellite loci were developed in Tsoongiodendron odorum, an endangered Magnoliaceae species in subtropical China, for further investigation of its conservation genetics.

METHODS AND RESULTS

Using the Fast Isolation by AFLP of Sequences Containing repeats (FIASCO) protocol, we isolated and characterized 12 microsatellite loci from T. odorum. Of the samples analyzed, eight were polymorphic and four were monomorphic.

CONCLUSIONS

These characterized markers will enable genetic diversity, gene flow, and mating system studies of T. odorum, which are highly valuable for formulating conservation strategies.

Development of microsatellite markers in Kmeria septentrionalis (Magnoliaceae), an endangered Chinese tree

PREMISE OF THE STUDY

Microsatellite markers were developed in an endangered plant, Kmeria septentrionalis, to investigate its population genetic structure, gene flow, and mating systems.

METHODS AND RESULTS

Using the combined biotin capture method, 14 microsatellite primer sets were isolated and characterized. All of these markers showed polymorphism, and the number of alleles per locus ranged from 3 to 15 across 60 individuals from two populations. The observed and expected heterozygosities ranged from 0.2692 to 0.9667 and from 0.3271 to 0.8881, respectively.

CONCLUSIONS

These markers will facilitate further studies on the genetic diversity and mating systems of K. septentrionalis.

Microsatellite genetic variation in small and isolated populations of Magnolia sieboldii ssp. japonica

Magnolia sieboldii ssp. japonica, distributed mainly in western Japan, is restricted to high elevation areas (1000-2000 m above sea level) and usually forms small isolated populations. Four microsatellite loci were assayed for 19 populations from six regions spanning the range of distribution, and the levels and distribution of genetic variation were estimated. All four loci were variable, with a total of 39 alleles, but the overall level of microsatellite genetic variation was low, especially compared with a related species, M. obovata. Genetic structure in M. sieboldii was characterised by low intrapopulational genetic variation (A = 3.74 and H(o) = 0.366 on average) and high genetic differentiation even among regional populations. Highly significant isolation-by-distance (IBD) models at the short distance were detected. Genetic drift and limited gene flow was considered to be important in determining the genetic structure within regions. Total genetic differentiation was remarkably high (F(ST) = 0.488 and R(ST) = 0.538), suggesting genetic barriers among regions. Neighbour-joining dendrograms relating the 19 populations, and further analysis on the IBD models, revealed that a stepwise mutation model was more suited than an infinite allele model to explain the genetic differentiation among regions. It is suggested that mutation at microsatellite loci might be influential in generating the genetic differentiation among regions. These results showed the potential of hypervariable microsatellite loci to evaluate the effects of genetic drift and population isolation within regions, and to detect genetic distinctiveness, in spite of the loss of overall genetic variation in M. sieboldii.

[Studies on DNA amplification fingerprinting of cortex Magnoliae officinalis]

Total genomic DNA samples of Chinese traditional medicine(CTM) Cortex Magnoliae Officinalis ("Houpo"), its counterfeits and substitutes were amplified by DNA amplification fingerprinting(DAF). Their amplified DNA banding patterns were distinguished on PAGE. The results show that DAF can be used to identify CTM "Houpo", its counterfeits and substitutes, which is also quite valuable for correctly introducing original plant.

RNA editing of the ribosomal protein S13 transcripts in magnolia and sunflower mitochondria

To obtain information on ribosomal protein gene content and RNA editing in plant mitochondria, we investigated the conservation of the gene for ribosomal protein S13 (rps13) in the mitochondrial genomes of Magnolia spp. and Helianthus annuus. A complete rps13 open reading frame was identified in the mitochondrial genome of Magnolia and Helianthus. Comparison of genomic and cDNA sequences revealed that transcripts from the mitochondrial rps13 locus in both Magnolia and Helianthus undergo RNA editing suggesting the functionality of the related gene. Six and four editing events in the rps13 transcript population of Magnolia and Helianthus mitochondria, respectively, cause critical changes of codons and, consequently, induce 5 and 3.4% amino acid modifications in the respective genomically-encoded S13 polypeptides. Both editing pattern and efficiency of RNA editing differ in the reverse transcription (RT)-PCR-derived cDNA populations from the rps13 locus from the analyzed plant species with only the Magnolia rps13 being fully edited.