2021 Volume 86 Issue 1 Pages 21-28
Artificial tetraploid and octaploid strains were induced from the wild species of Drosera rotundifolia (2n=2x=20) and D. anglica (2n=4x=40), respectively. The optimal condition of colchicine-treatments for polyploid inductions was determined first. A flow cytometry (FCM) analysis showed that the highest mixoploid score of D. rotundifolia was 20% in the treatment of 0.3% for 2 days (d), or 0.5% for 3 d, while the highest mixoploid score of D. anglica was 20% in the treatment of 0.5% for 2 d. Next, to remove chimeric cells, adventitious bud inductions were carried out using the FCM-selected individuals in both species. One strain from a total of 360 colchicine-treated leaf explants in each species had pure chromosome-double numbers of 2n=40 (tetraploid) in D. rotundifolia and 2n=80 (octaploid) in D. anglica. In both species, the guard cell sizes of the chromosome-doubled strains were larger than those of the wild types. The leaves of the chromosome-doubled strains of D. rotundifolia were larger than those of the wild diploid D. rotundifolia, while the leaves of the chromosome-doubled strains of D. anglica were smaller than those of the wild tetraploid D. anglica.
The genus Drosera (sundew), which is the second-largest genus of carnivorous plants (Seine and Barthlott 1994), consists of nearly 150 species with high genetic diversity (Rivadavia et al. 2003, Eschenbrenner et al. 2019). Many Drosera species are a natural source of pharmacologically important compounds (Banasiuk et al. 2012), creating 200–300 registered medications for coughs and pulmonary diseases in Europe (Baranyai and Joosten 2016). Nowadays, huge amounts of the plants in these species are required for a continuing demand from pharmaceutical companies. Especially, a representative species D. rotundifolia L., which is the main herb of the medicine “Droserae Herba,” has been traditionally used in the treatment since the 17th century (Paper et al. 2005). The other species such as D. anglica Huds., D. burmannii Vahl, D. indica L., D. intermedia Hayne, D. madagascariensis DC., D. peltata Thunb. and D. ramentacea Burch. ex DC. are also officially permitted for pharmaceutical purposes in European countries (Baranyai and Joosten 2016). Except for D. burmannii, D. indica, and D. peltata, all the officially permitted species taxonomically fall into section Drosera, according to the taxonomic system of Seine and Barthlott (1994) [formerly classified within series Eurossolis of section Rossolis in subgenus Rorella of Diels’ (1906) classification]. In this section, D. anglica is a phylogenetically derivative species with large plant size and could be easily distinguished from the other species by high chromosome number and large genome size seeming to arise through natural polyploidization event (Kondo and Segawa 1988), even though it is quite closely related to D. rotundifolia based on cytological and molecular data (Wood 1955, Hoshi et al. 2008). Thus, we expect that D. anglica is a candidate species for the breeding improvement of sundews, as well or better than D. rotundifolia.
Polyploid induction with chromosome doubling is an important protocol for plant breeding because even in nature the polyploids generally show strong environmental adaptation and diverse variations (Wang et al. 2020). The artificially induced polyploid plants also often appear to have superior characteristics to the progenitor in morphology, metabolite, and yield performance (Xiong et al. 2006, Zhou et al. 2020). Therefore, the chromosome doubling technique for inducing polyploids has been reported for some plant species (Soltis et al. 2003, Hannweg et al. 2013). However, the breeding to create the new polyploid strain has not yet been extensively carried out in this genus.
Expecting a high yielding effect of Drosera species as medicinal herbs, the present study aims to establish artificially chromosome-doubled strains induced from the wild species of D. rotundifolia and D. anglica. The optimal condition of colchicine-treatments for polyploid inductions was determined first, and then screened individuals in each species were characterized by FCM, chromosome counting, and guard cell measurements. Moreover, the chromosome-doubled strains were compared with the wild types of each species to infer the speciation of the studied member of section Drosera.
Two wild types of Drosera rotundifolia L. (accession No. 010816sera1, 2n=2x=20) and D. anglica Huds. (Accession No. KF-01, 2n=4x=40) were used as the original strains for polypoid inductions. These materials were obtained from tissue-cultured seedlings from aseptic-treated seeds sown on half-strength Murashige–Skoog’s (1/2 MS) basal medium (Murashige and Skoog 1962), supplemented with 3.0% sucrose and 0.2% gellan gum (pH 5.7 before autoclaving), and were subcultured in the same medium. These strains were maintained in vitro in the Laboratory of Plant Environment Science, Department of Plant Science, School of Agriculture, Tokai University.
Polyploid inductionThe procedure of colchicine treatment was employed following the protocol of Tungkajiwangkoon et al. (2016). Adventitious buds were produced from young leaves by tissue culture in 1/2 MS liquid medium supplemented with 1.0% sucrose after transferring. The buds were soaked in 0%, 0.1%, 0.3%, and 0.5% colchicine solutions for 1, 2 and 3 d (30 adventitious buds per treatment). They were then cultured on 1/2 MS solid medium supplemented with 3.0% sucrose and 0.2% gellan gum at 25°C under continuous light conditions.
Ploidy analysis by FCMTen young leaves cultured in vitro were chopped in 1.0 mL of a nuclei isolation buffer (NE buffer) containing 50 mM Tris–HCl (pH 7.5), 50 mM Na2SO3, 140 mM 2-mercaptoethanol, 2 mM MgCl2, 2% (w/v) PVP K-30, 1% (v/v) Triton X-100, and 25 µg mL−1 propidium iodide. Then, the chopped samples were filtered through a 48-µm nylon mesh and centrifuged with 12,000 rpm for 2 min at room temperature (RT). After centrifuging, the pellets including isolated nuclei were suspended with 0.2 mL NE buffer. After incubating the samples for 5 min at RT, the DNA contents of nuclei were measured using a flow cytometer (Guava EasyCyte 12HT microcapillary flow cytometer, Millipore). Five thousand nuclei acquired at a flow rate of 0.12 µL s−1 were used for each FCM measurement and at least three replicates were measured for each strain. Young leaves of Oryza sativa L. ‘Nipponbare’ (2C value=0.91 pg, Uozu et al. 1997) as a reference standard were used to estimate genome size in the absolute unit. Conversion of weight into the number of base-pairs was also calculated using the value of 1 pg=978 Mbp (Doležel et al. 2003).
Fluorescent staining with DAPIFor mitotic chromosome observations, the DAPI staining technique was performed according to Hoshi and Kondo (1998 a, b) and was simplified the procedure for Drosera chromosome counting. Root tips in vitro were collected and pretreated with 0.05% colchicine for 2 h at 18°C before fixation in 45% acetic acid for 30 min on ice. Then, they were hydrolyzed in a mixture of 1 M HCl and 45% acetic acid (2 : 1) at 60°C for 7 s. The hydrolyzed root-tip meristems were isolated on glass slides, and well-spread meristem cells in 45% acetic acid were squashed under coverslips. After removing frozen coverslips, the chromosomes were air-dried at RT. Then, the chromosomes were stained with 1 µg mL−1 DAPI in McIlvaine’s buffer, containing 50% glycerol. The chromosomes stained with DAPI were observed under an epifluorescence microscope (BX51, Olympus) with a U-MWU2 filter. Digital images were taken with a DP73 digital camera (Olympus) on the fluorescence microscope. More than 100 metaphase cells were observed in each strain to check for chromosomal aberrations and chimeric cells in each artificial strain. Since the Drosera chromosomes at mitotic metaphase have no primary constriction or localized centromere (Kondo and Lavarack 1984, Kondo and Segawa 1988, Sheikh et al. 1995, Hoshi and Kondo 1998a, b, Shirakawa et al. 2011), they could not be classified by the conventional method using the position of the localized centromere (Levan et al. 1964). Therefore, the chromosome classification of Drosera followed Kondo (1976), and the nomenclature for the karyotype symbols followed Shirakawa et al. (2012). Chromosome sizes were defined as s=small chromosome (shorter than 1.0 µm), and m=middle chromosome (1.0–2.4 µm).
Observation of leaf guard cellsGuard cell lengths and widths of the wild strains and the colchicine-induced strains were measured on 30 guard cells per strain. Guard cell sizes were measured from the lower epidermis in the middle parts of the leaves using ImageJ software (ver. 1.45s).
The results of survival rates and polyploid frequencies of D. rotundifolia and D. anglica after colchicine treatments are shown in Table 1. A few treatments caused phytotoxic effects. The survival rates were recorded after 10 weeks. The control groups for 1 d treatments of D. rotundifolia and D. anglica had the highest survival rate (Table 1). The other control groups of longer treatments showed lower survival rates than those of 1 d (Table 1). Morphological changes of the colchicine-treated individuals were observed in both species (figure not shown). Bell-shaped leaves of D. rotundifolia and D. anglica were seen in colchicine treatments of 0.5% for 3 d and 0.1% for 1 d, respectively. In contrast, heart-shaped leaves were seen in D. rotundifolia treated with 0.1% for 3 d. Rarely, a separation at the basal part of the leaf blade was observed in D. anglica treated with 0.3% for 1 d. After the colchicine treatment, mixoploids or chimeric plants could be detected by FCM. The highest mixoploid score of D. rotundifolia was 20% in the treatment of 0.3% for 2 d and 0.5% for 3 d, while the highest mixoploid score of D. anglica was 20% in the treatment of 0.5% for 2 d (Table 1).
| Concentration of colchicine (%) | Treatment time (d) | Total number of explants | D. rotundifolia | D. anglica | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Survival rate (%) | Number of mixoploid | Frequency of mixoploid (%) | Number of tetraploid | Frequency of tetraploid (%) | Survival rate (%) | Number of mixoploid | Frequency of mixoploid (%) | Number of octaploid | Frequency of octaploid (%) | |||
| 0 | 1 | 30 | 76.7 | 0 | 0.0 | 0 | 0.0 | 80.0 | 0 | 0.0 | 0 | 0.0 |
| 2 | 30 | 73.3 | 0 | 0.0 | 0 | 0.0 | 50.0 | 0 | 0.0 | 0 | 0.0 | |
| 3 | 30 | 36.7 | 0 | 0.0 | 0 | 0.0 | 40.0 | 0 | 0.0 | 0 | 0.0 | |
| 0.1 | 1 | 30 | 30.0 | 1 | 3.3 | 0 | 0.0 | 30.0 | 1 | 3.3 | 0 | 0.0 |
| 2 | 30 | 26.7 | 1 | 3.3 | 0 | 0.0 | 60.0 | 2 | 6.7 | 0 | 0.0 | |
| 3 | 30 | 46.7 | 4 | 13.3 | 0 | 0.0 | 66.7 | 5 | 16.7 | 0 | 0.0 | |
| 0.3 | 1 | 30 | 60.0 | 1 | 3.3 | 1 | 3.3 | 46.7 | 3 | 10.0 | 0 | 0.0 |
| 2 | 30 | 63.3 | 6 | 20.0 | 0 | 0.0 | 33.3 | 3 | 10.0 | 0 | 0.0 | |
| 3 | 30 | 36.7 | 2 | 6.7 | 0 | 0.0 | 30.0 | 1 | 3.3 | 1 | 3.3 | |
| 0.5 | 1 | 30 | 43.3 | 1 | 3.3 | 0 | 0.0 | 33.3 | 0 | 0.0 | 0 | 0.0 |
| 2 | 30 | 36.7 | 3 | 10.0 | 0 | 0.0 | 40.0 | 6 | 20.0 | 0 | 0.0 | |
| 3 | 30 | 56.7 | 6 | 20.0 | 0 | 0.0 | 60.0 | 4 | 13.3 | 0 | 0.0 | |
The wild types (original strains) of D. rotundifolia and D. anglica showed that somatic chromosome numbers of 2n=20 and 2n=40, respectively (Fig. 1). Most of the colchicine-induced individuals were the same as the wild types showing a single peak of FCM or chimeric formations detected as two peaks of FCM. A few individuals displayed an FCM peak showing double genome size, being judged as they just consisted of nuclei with chromosome-doubling (Table 1). In both species, on the other hand, chromosome observation recognized chimeric structures in the individuals even after screening by FCM profile, indicating a detection limit of FCM. In this instance of the FCM screening, all selected individuals possessed mixoploid somatic cells of 2n=2x=20m and 2n=4x=40m in D. rotundifolia, and of 2n=4x=40m and 2n=8x=80m in D. anglica.
To establish chromosome-doubled strains, the second screening was therefore carried out by adventitious bud induction from the FCM-selected individuals. After the second screening, one strain from a total of 360 colchicine-treated leaf explants in each species had pure counts of chromosome numbers of 2n=40 in D. rotundifolia and 2n=80 in D. anglica (Fig. 1).
In genome size estimation, the 2C value of the chromosome-doubled strain (4×05-10-15) of D. rotundifolia was 5.34 pg, while the 2C value of the chromosome-doubled strain (8×03-3-26) in D. anglica was 11.12 pg (Fig. 2, Table 2). Comparing with the wild types, the chromosome-doubled strains in both species showed twice the values of 2C DNA contents. As the result of the second screening, we isolated a synthetic chromosome-doubled strain in each species from several mixoploid clones, and finally established the tetraploid D. rotundifolia and the octaploid D. anglica (Table 2).
| Species | Strain | Type | Chromosome number (2n) | Ploidy level (x) | 2Ca (pg) | DNA amount of 2C (Mbp) | 1C (pg) | 1Cx (pg) |
|---|---|---|---|---|---|---|---|---|
| D. rotundifolia | 010816-sera-1 | Wild | 20 | 2 | 2.73±0.07 | 2,670 | 1.37 | 1.37 |
| 4×05-10-15 | Artificial | 40 | 4 | 5.34±0.10 | 5,223 | 2.67 | 1.34 | |
| D. anglica | KF-01 | Wild | 40 | 4 | 5.67±0.22 | 5,545 | 2.84 | 1.42 |
| 8×03-3-26 | Artificial | 80 | 8 | 11.12±0.35 | 10,875 | 5.56 | 1.39 | |
| Oryza sativa | Nipponbare | Wild | 24 | 2 | 0.91±0.00 | 890 | 0.46 | 0.46 |
aMean±SD
Figure 3 and Table 3 show guard cell sizes among the wild types and the chromosome-doubled strains of D. rotundifolia and D. anglica. In both species, the guard cell sizes of the chromosome-doubled strains were larger than those of the wild types. Additionally, the guard cell length of the artificial tetraploid D. rotundifolia was larger than that of the wild tetraploid D. anglica. The leaves of the chromosome-doubled strains of D. rotundifolia were larger than those of the wild diploid D. rotundifolia (Fig. 4A, B), while the leaves of the chromosome-doubled strains of D. anglica were smaller than those of the wild tetraploid D. anglica (Fig. 4C, D).
| Species | Type | Ploidy level (x) | Mean length±SD (µm) | Mean width±SD (µm) |
|---|---|---|---|---|
| D. rotundifolia | Wild | 2 | 43.2a±4.77 | 22.0a±1.85 |
| Artificial | 4 | 50.0b±4.45 | 29.1b±6.51 | |
| D. anglica | Wild | 4 | 42.4a±2.92 | 26.7b±2.56 |
| Artificial | 8 | 49.3b±3.20 | 28.9b±1.75 |
a, bDifferent letters within the same columns indicate statistically significant difference using Duncan’s test at 95% (p＜0.05).
This is the first report of inductions of polyploidizations in D. rotundifolia and D. anglica. The tetraploid (2n=40) and octaploid (2n=80) strains were created by chromosome doubling from the wild types of D. rotundifolia (diploid) and D. anglica (tetraploid), respectively. Although polyploid inductions are not always successful and often lead to a small number of plants with chromosome duplications (Oliveira et al. 2004), the technique of colchicine-induced polyploidization has long been used in breeding programs of many plant species (Sattler et al. 2016). Only a few attempts, however, have been made to induce chromosome-doubled individuals in Drosera. Zahumenicka et al. (2013) induced artificial octaploids by treating leaf segments of wild type of D. capensis (2n=40) in vitro using oryzalin in appropriate combination with concentration and duration. Charoenwattana (2014) used colchicine to produce tetraploids from plantlet in vitro of the diploid D. spatulata (2n=20), and obtained the chromosome-doubled strains treated with lower concentrations (6 or 12 mg L−1) for longer period (7 d). In contrast, Tungkajiwangkoon et al. (2016) created the colchicine-induced hexaploids from adventitious buds generated on leaf explants in vitro of the triploid hybrid of D. rotundifolia (2n=20) and the tetraploid D. spatulata (2n=40), by treating with high concentrations (50 or 100 mg L−1) for short periods (1 d or 3 d). The concentration, duration, and explant type for the mitosis inhibitor treatment is a key to success for polyploidy induction (Kazi et al. 2015, Eng and Ho 2019), due to toxic effects of the treatment (Trojak-Goluch and Skomra 2013). Our experiments showed that the chromosome-doubled strains were induced from two species successfully using the higher concentration solutions for the short periods and demonstrated a time-saving advantage to make chromosome doubling with high incidence rate. All of these articles shared the successful induction of polyploidy using in vitro materials such as buds, leaves, and plantlets. As a consequence of our investigation, we concluded that adventitious buds could be one of the most effective explants for colchicine induction in Drosera species.
Polyploid effects in DroseraOur results of comparison of the guard cell sizes within the species indicated that the sizes of chromosome-doubled strains were larger than those of wild strains in both species. On the other hand, the comparison between the species interestingly revealed that the guard cell size of the artificial tetraploid D. rotundifolia was larger than that of the wild tetraploid D. anglica, in addition to the same sizes between the wild diploid D. rotundifolia and the wild tetraploid D. anglica. Moreover, our strains maintained in vitro unexpectedly showed that the octaploid D. anglica produced shorter leaf than that of the tetraploid D. anglica. In contrast, the artificial D. rotundifolia produced larger leaf than that of wild D. rotundifolia, expecting a high yield of biomass in the tetraploid strain. Generally, plants show a positive correlation between ploidy and sizes of guard cells and/or organs due to the “gigas effect” (Stebbins 1950) of polyploidy or whole-genome duplication, as mentioned in many reviews (e.g., Sattler et al. 2016). Even our materials were closely related to each other, no obvious correlation was, however, found neither between the wild strains of both species nor between the tetraploid and octaploid of D. anglica, suggesting due to genetic or genome-constitutional differences between them.
In nature, the maximum ploidy level in the genus Drosera is the octaploid with 2n=8x=80s (2C=1,949 Mbp, Veleba et al. 2017) seen in D. aliciae Hamet belonging to section Drosera possessed s chromosomes, whereas the highest ploidy with m chromosomes is the tetraploid known as D. anglica (2n=4x=40m). A few papers reported genome size (2C value) in D. anglica and could give it an estimation of ca. 5,000 Mbp (4,715 Mbp in Veleba et al. 2017, 5,545 Mbp in Hoshi et al. 2017). In section Drosera, the tetraploid species possessed s chromosomes are rather common, while all species possessed m chromosomes are the diploids with one exception of D. anglica (Kondo and Segawa 1988). Additionally, the highest genome size is 2C=5,930 Mbp in the diploid species D. filiformis Raf. var. tracyi (Macfarlane) Diels (Veleba et al. 2017). Therefore, the octaploid (2n=8x=80m) with 2C vale more than 10,000 Mbp created in this study does not exist in nature. Kawamura (1981) mentioned the “limit” of polyploid production resulting from a tendency to decrease the sizes of cell and plant body in an excessively high level of polyploid. Based on our morphological data together with previous reports (Hoshi and Kondo 1998a, Veleba et al. 2017), we speculate that the octaploid might be the limit of polyploid production in Drosera.
Polyploid speciation and formation of monomodal karyotype in D. anglicaThe tetraploid D. rotundifolia and the octaploid D. anglica were artificially produced, while D. rotundifolia and D. anglica only show the diploid and the tetraploid in nature, respectively. Despite morphological and ploidy differences between the two wild species, previous molecular phylogenic data showed that D. anglica is the most closely related species to D. rotundifolia (Hoshi et al. 2008). Additionally, the cytogenetic insight between these species suggested that D. rotundifolia was involved in the origin (or speciation) of D. anglica (Wood 1955). Given the great crossability in natural mating between these species, their evolutionary relationships, species differentiation, and especially the speciation with polyploidization of D. anglica has, therefore, a long time been controversial and even today remain under discussion. Polyploidy is widely acknowledged as a major mechanism of adaptation and speciation in plants (Ramsey and Schemske 1998). Two distinct categories of polyploids, autopolyploid and allopolyploid, are generally recognized. The tetraploid D. rotundifolia induced by colchicine from the diploid is, therefore, autopolyploid with a monomodal karyotype, which is characterized by the almost same size of chromosomes. In many angiosperms, the symmetrical karyotypes are correlated with the primitive condition of the taxa (Stebbins 1971), whereas a bimodal karyotype, which characterized by the presence of two sets of chromosomes of contrasting size. As countless cytogenetic studies (e.g., Bennett et al. 1992) have been conducted that the bimodal karyotypes in angiosperms could be derived from 1: unequal translocations (Stebbins 1971), 2: loss of DNA from one set of assumed homoeologous chromosomes in polyploid with symmetrical karyotype (Darlington 1963), and 3: allopolyploidy involving the unification of genetically dissimilar genomes (Brandham 1983). In the case of Drosera, D. anglica and its related species, which distribute mainly in North America and some of them are widespread to the Northern Hemisphere, show monomodal karyotypes consisting of m chromosomes, without any exception (Kondo and Segawa 1988, Hoshi and Kondo 1998a). Additionally, all of the North American species are diploids, except for D. anglica. In contrast, bimodal karyotypes were always recognized in artificial hybrids of D. anglica, crossed by its closely related species, D. capillaris Poir., D. filiformis Raf., D. intermedia, and even D. rotundifolia (Kondo and Segawa 1988), suggesting that bimodality of the group in Drosera could be due to the allopolyploidy with different genomes by the hybrid event. Moreover, distinct bimodalities ware also observed in natural diploid hybrid D.×hybrida Macfarlane (D. filiformis×D. intermedia Macfarlane) and amphihexaploid spesies D. tokaiensis (Komiya & C. Shibata) T. Nakamura & Ueda (Hoshi and Kondo 1998a). Therefore, the allopolyploidy seems to be the main mechanism to form karyotype bimodality in this group of Drosera.
Meiotic observations by some researchers have been given the evidence of amphidiploidal origin of D. anglica with two genomes of D. rotundifolia or its related ancestral species, since MI confirmation of D. anglica and D. obovata Mert. et Koch (D. rotundifolia×D. anglica Lasch) showed 20II and 10II+10I, respectively (Rosenberg 1909, Shimamura 1941, Wood 1955, Kondo and Segawa 1988). The remained genomes seem to be D. linearis Goldie, due to the observation of meiotic behavior of the hybrid between D. anglica × D. linearis, shown 10II+10I (Wood 1955). Another observation of leaf morphologies also supports the parental species of the allopolyploidal hybrid origin of D. angrica, showing intermediate shape between these species (Wood 1955): D. linearis has long leaves with linear leaf-blades, while D. rotundifolia has spoon-type leaves with orbicular leaf-blades. Additionally, our results also supported that remained genome of D. anglica could be from another species with phenotypic influence allopolyploidally, but not autopolyploidally as D. rotundifolia, since the leaf morphology of our chromosome-doubling strain of the tetraploid D. rotundifolia showed spoon-type shape as same to that of the wild diploids. Until now, cytological information of genome size and chromosome sizes has been a lack in D. linarias. Thus, a speculation of the cytological similarities between D. linearis and D. rotundifolia was given from our results of chromosome observation and FCM analysis, indicating that the artificial autotetraploid D. rotundifolia showed not only monomodal karyotype but also 2C value is same to that of the wild allotetraploid D. anglica. Even though we could simply speculate the monomodal forming in D. anglica by adding or subtracting the similar 2C values of D. linearis and D. rotundifolia, the fact of bimodal karyotype formation in hybrid without any exception made us difficult to conclude same sizes of chromosomes or genomes between D. linearis and D. rotundifolia. A genome size reduction after speciation has been discussed in some plant species with amphiploid origin (Ozkan et al. 2003), including in Drosera (Tungkajiwangkoon et al. 2016). Tungkajiwangkoon et al. (2016) compared the genome sizes between wild amphidiploidal species D. tokaiensis and the artificial hexaploid created by chromosome doubling of triploid hybrid between D. rotundifolia and D. spatulata Labill. Eventually, the artificial hybrid showed distinctly higher 2C values than that of wild species D. tokaiensis, suggesting the genome size reduction arose in wild species of D. tokaiensis. This experimental research led us to suggest that the same rule of the reduction event of genome size has occurred in D. anglica. D. anglica could involve the monomodal formation after amphiduplication event with bimodality. Therefore, the formation of monomodality with genome size change might be of special significance for establishing new species during the speciation after allopolyploidal hybridization in the genus Drosera.
Our study together with further comparative investigations into the whole genome sequences of different types of genomes will help to elucidate the mechanisms of chromosome change, and to improve breeding strategies in Drosera.
