Biology subjects

Schubert, I.

Publications and source records attributed to Schubert, I..

6 recordsLinked to original sources

bioRxiv2026

Newly unveiled meiosis elucidates the unreduced gamete frequency and its impact on evolution of the Lemna minor complex

Fusion of gametes possessing meiotically reduced (haploid) chromosome complements is the main pathway of propagation among eukaryotes. However, duckweeds, the smallest angiosperms, propagate mainly vegetatively, and meiosis has not yet been documented in detail for this plant family. The more surprising was the recent evidence of rather frequent interspecific hybrids and triploid clonal accessions which became obvious by genome size measurements, genomic in situ hybridization (GISH) and combined plastid and nuclear DNA markers. These observations indicated sexual propagation involving reduced as well as unreduced male and female gametes in Lemna minor and L. turionifera leading to allodiploid and allotriploid hybrids (MT, MMT, MTT) and autotriploid L. minor (MMM) accessions. Here, we i) documented the meiotic stages of Lemna species for the first time; ii) provided evidence of unreduced male gametes through fluorescent in situ hybridization (FISH) with single locus probes; iii) determined their abundance in different individuals and iv) hypothesized about the reasons of unreduced male gamete formation. These findings open new insights into the modes of sexual reproduction and evolution of duckweeds which may be useful for future breeding efforts in this emerging crop.

plant biology↗

bioRxiv2025

Hybridity of mainly asexually propagating duckweeds in genus Lemna - dead end or breakthrough?

O_LIThe cosmopolitan, mainly vegetatively propagating, organ-reduced monocotyledonous aquatic duckweeds are the smallest and fastest growing angiosperms, distributed world-wide and flower rarely in nature. Recently, we reported intra- and interspecific hybrids and ploidy variants in the genus Lemna. Thus, contrary to the expectation, sexual propagation may occasionally occur within and between Lemna species. Our main goal was to uncover whether the ecologically successful hybrids are evolutionary dead ends, or initiate further speciation and novel sexual recombination. C_LIO_LIWe investigated flower development, pollen viability, seed set and seed germination in hybrids and their parental species and characterized genome size and genetic markers in the progenies. C_LIO_LIIntraspecific crosses yielded fertile progeny, but all dihaploid and triploid interspecific hybrids were male sterile. Only an established allotetraploid hybrid reproduced sexually, while colchicine-induced allotetraploids from dihaploids did not re-gain sexual competence so far. C_LIO_LIWe concluded that only established allotetraploid hybrids represent an evolutionary break-through in duckweeds. Our results regarding sexual traits within the duckweed genus Lemna, and the sexual competence of diverse hybrids i) pave the way for further investigation in this understudied field, ii) provide fundamental data regarding the evolutionary potential of duckweed hybrids and iii) are important for future breeding efforts on this emerging crop. C_LI

evolutionary biology↗

bioRxiv2025

Triploidy is prominent in the duckweed Lemna minor complex

Duckweeds (Lemnaceae Martinov) are aquatic monocotyledonous flowering plants comprising five genera and 35 recognized species, known for being the smallest and fastest-growing flowering plants on Earth. Many species are morphologically indistinguishable due to their highly reduced structures, yet molecular evidence suggests that visually similar clones may represent distinct species or hybrids. For example, clonal accessions of the globally distributed Lemna minor in the Landolt Duckweed Collection exhibit genome size variations of several hundred megabases (Mb), raising questions about their taxonomic classification and evolutionary origins. We analyzed 58 presumed L. minor clones to resolve these relationships using a comprehensive suite of methods, including whole-genome sequencing (WGS), flow-cytometric genome size measurements, molecular markers, chromosome counting, and genomic in situ hybridization (GISH). Our findings reveal extensive genome plasticity within the "Lemna minor complex," identifying diploid and triploid L. minor clones, as well as di-haploid and triploid interspecific hybrids called L. x japonica (L. minor x L. turionifera), L. x mediterranea (L. minor x L. gibba), and a novel African-clade distinct from known L. minor lineages. Triploidy was prevalent, occurring in 29% of the clones, and was associated with enhanced growth under optimal conditions but reduced performance under high light and temperature. These findings highlight the widespread role of triploidy, cryptic species, and hybridization in the L. minor complex, emphasizing the importance of multiple approaches for accurately classifying duckweed species and understanding their evolutionary trajectories.

plant biology↗

bioRxiv2025

Complete genome sequence assembly elucidates evolution and regulation of 5S rDNA loci in the greater duckweed Spirodela polyrhiza

We resolved the molecular architecture of the 5S rDNA loci in an aquatic monocot Spirodela polyrhiza. Measurements of fluorescence in situ hybridization signals revealed two loci with 5S rDNA clusters. A combination of the extra-long DNA reads and conventional sequencing of 5S rDNA repeats allowed the assembling of complete loci sequences located on ChrSp6 and ChrSp13. The homologous chromosomes of the ChrSp6 locus contain clusters of 40 and >60 copies of 5S rDNA repeat units with intergenic spacer (IGS) of 400 bp. The ChrSp13 locus is represented by 5S rDNA clusters of rRNA genes spaced by IGSs of 1,056 or 1,069 bp arranged in two sub-clusters, suggesting a different rate of repeat homogenization between loci. The G/C-rich 5S rDNA arrays in both loci are embedded in A/T-enriched chromosome regions with possible regulatory functions. The TATA-like boxes of the 5S rDNA repeat on ChrSp6 and ChrSp13 exhibit different affinities for the TATA-binding protein in 3D modeling of protein/DNA interactions, suggesting a locus-specific regulation of rRNA transcription. Our findings shed light on the molecular architecture of the 5S rDNA loci, which could foster an innovative era for the principles of evolution and regulation of rRNA genes in plants.

molecular biology↗

bioRxiv2025

Genome diversity and phylogeny of the section Alatae of genus Lemna (Lemnaceae), comprising the presumed species Lemna aequinoctialis, Le. perpusilla and Le. aoukikusa

O_LIThe Section Alatae of genus Lemna of the monocotyledonous aquatic duckweed family (Lemnaceae) consists of rather diverse accessions with unknown phylogeny and unclear taxonomic assignment. In contrast to other duckweeds, some Alatae accessions, in addition to mainly vegetative propagation, produce readily flowers and viable seeds. We analyzed the genomic diversity and phylogenetic relationship of 52 Alatae accessions. C_LIO_LIFor this purpose, we applied multiple molecular and cytogenetic approaches, including plastid and nuclear sequence polymorphisms, chromosome counting, genome size determination and genomic in situ hybridization in combination with geographic distribution. C_LIO_LIWe uncovered ploidy variation, recurrent hybridization, and backcrosses between diploid species and their hybrids. The latter successfully spread over three continents. C_LIO_LIThe results elucidate the evolution of Alatae accessions (summarized in Fig. 7) and explain the difficult taxonomic assignment of distinct accessions. Our study might be an example for analogous studies to resolve the hitherto unclear relationships among accessions of the duckweed genera Wolffiella and Wolffia. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=166 SRC="FIGDIR/small/632899v1_fig7.gif" ALT="Figure 7"> View larger version (23K): org.highwire.dtl.DTLVardef@d05f08org.highwire.dtl.DTLVardef@f33c5org.highwire.dtl.DTLVardef@ff7adorg.highwire.dtl.DTLVardef@4da6e4_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 7C_FLOATNO Hypothetical scenario of evolution within Lemna Section Alatae. In bold are accessions from America. The classically defined diploid species Le. aequinoctialis and Le. perpusilla sensu stricto were confirmed by the applied molecular methods. The previously named Le. aoukikusa accessions were uncovered as tetraploid interspecific hybrids between Le. aequinoctialis and Le. perpusilla. In addition, further tri- and tetraploid hybrids as well as tri- and tetraploid "Backcross hybrids" were detected from the USA and China, respectively. C_FIG

evolutionary biology↗

bioRxiv2023

The genomes and epigenomes of aquatic plants (Lemnaceae) promote triploid hybridization and clonal reproduction

The Lemnaceae (duckweeds) are the worlds smallest but fastest growing flowering plants. Prolific clonal propagation facilitates continuous micro-cropping for plant-based protein and starch production, and holds tremendous promise for sequestration of atmospheric CO2. Here, we present chromosomal assemblies, annotations, and phylogenomic analysis of Lemna genomes that uncover candidate genes responsible for the metabolic and developmental traits of the family, such as anatomical reduction, adaxial stomata, lack of stomatal closure, and carbon sequestration via crystalline calcium oxalate. Lemnaceae have selectively lost genes required for RNA interference, including Argonaute genes required for reproductive isolation (the triploid block) and haploid gamete formation. Triploid hybrids arise commonly among Lemna, and we have found mutations in highly-conserved meiotic crossover genes that could support polyploid meiosis. Syntenic comparisons with Wolffia and Spirodela reveal that diversification of these genera coincided with the "Azolla event" in the mid-Eocene, during which aquatic macrophytes reduced high atmospheric CO2 levels to those of the current ice age. Facile regeneration of transgenic fronds from tissue culture, aided by reduced epigenetic silencing, makes Lemna a powerful biotechnological platform, as exemplified by recent engineering of high-oil Lemna that outperforms oil seed crops.

plant biology↗