Abstract
The monophyletic carnivorous genus Genlisea (Lentibulariaceae) is characterized by a bi-directional genome size evolution resulting in a 25-fold difference in nuclear DNA content. This is one of the largest ranges found within a genus so far and makes Genlisea an interesting subject to study mechanisms of genome and karyotype evolution. Genlisea nigrocaulis, with 86 Mbp one of the smallest plant genomes, and the 18-fold larger genome of G. hispidula (1,550 Mbp) possess identical chromosome numbers (2n = 40) but differ considerably in chromatin organization, nuclear and cell size. Interphase nuclei of G. nigrocaulis and of related species with small genomes, G. aurea (133 Mbp, 2n ≈ 104) and G. pygmaea (179 Mbp, 2n = 80), are hallmarked by intensely DAPI-stained chromocenters, carrying typical heterochromatin-associated methylation marks (5-methylcytosine, H3K9me2), while in G. hispidula and surprisingly also in the small genome of G. margaretae (184 Mbp, 2n = 38) the heterochromatin marks are more evenly distributed. Probes of tandem repetitive sequences together with rDNA allow the unequivocal discrimination of 13 out of 20 chromosome pairs of G. hispidula. One of the repetitive sequences labeled half of the chromosome set almost homogenously supporting an allopolyploid status of G. hispidula and its close relative G. subglabra (1,622 Mbp, 2n = 40). In G. nigrocaulis 11 chromosome pairs could be individualized using a combination of rDNA and unique genomic probes. The presented data provide a basis for future studies of karyotype evolution within the genus Genlisea.
Highlights
The bladderwort family, Lentibulariaceae, belonging to the eudicot order Lamiales comprises three genera of distinct morphology, Utricularia, Pinguicula, and Genlisea
G. nigrocaulis and G. hispidula Differ in Genome, Nucleus and Cell Size The nuclear DNA content of G. nigrocaulis was estimated to be 0.088 pg/1C corresponding to 86 Mbp according to the conversion proposed by Dolezel et al (2003), while that of G. hispidula was estimated to be 1,590 pg/1C corresponding to 1,550 Mbp (Vu et al, in review)
The Small Genome of G. nigrocaulis Displays Distinct Heterochromatin Features DAPI-staining of flow-sorted interphase nuclei revealed surprisingly distinct heterochromatic chromocenters in the small genome of G. nigrocaulis (Figure 3B), while nuclei of the 18-fold larger genome of G. hispidula displayed a nearly homogeneous DAPI staining without conspicuous heterochromatin clusters (Figure 4B)
Summary
The bladderwort family, Lentibulariaceae, belonging to the eudicot order Lamiales comprises three genera of distinct morphology, Utricularia (bladderworts), Pinguicula (butterworts), and Genlisea (corkscrew plants; Mueller et al, 2003, 2006). The more than 300 different species of the Lentibulariaceae are small, herbaceous and predominantly hydrophytes or aquatic (Utricularia) plants. All species within this family are carnivorous and each of the three genera developed a distinct trapping mechanism. Pinguicula species use sticky, glandular leaves (flypaper traps) to catch small insects. Utricularia species have subterraneous leaves forming unique bladder-shaped suction traps to catch mainly aquatic animals and phytoplankton.
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