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The CRISPR/Cas9 genome editing system has already proved its efficiency, versatility and simplicity in numerous applications in human, animal, microbe and plant cells. Together with the vast amount of genome and transcriptome databases available, it represents an enormous potential for plant breeding and research. Although most changes produced with CRISPR/Cas9 do not differ from naturally occurring mutations, the use of transgenesis during varietal development can still trigger GMO legislation in countries that rely on process-based regulation. Moreover, stable integration of DNA coding for genome-editing tools into plant genomes can result in insertional mutagenesis, while its prolonged expression can cause mutations in off-target sites. These pitfalls can be avoided with the delivery of preassembled ribonucleoprotein complexes (RNPs) composed of purified recombinant enzyme Cas9 and -transcribed or synthesized sgRNA. We therefore aimed to develop a DNA-free protocol for site-directed mutagenesis of three species of the genus ( , and ) with the use of RNPs. We chose cabbage, rapeseed and Chinese cabbage as species representatives and introduced RNPs into their protoplasts with PEG 4000. Four sgRNAs targeting two endogenous genes (the and genes, two sgRNAs per gene) were introduced into all three species. No mutations were detected after transfection of rapeseed protoplasts, while we obtained mutation frequencies of 0.09 to 2.25% and 1.15 to 24.51% in cabbage and Chinese cabbage, respectively. In both species, a positive correlation was displayed between the amount (7.5, 15, 30, and 60 μg) of Cas9 enzyme and sgRNA introduced and mutation frequency. Nucleotide changes (insertions and deletions) were detected 24 h after transfection and did not differ 72 h after transfection. They were species-, gene- and locus-dependent. In summary, we demonstrated the suitability of RNP transfection into and protoplasts for high-efficiency indel induction of two endogenous genes. Due to the relatively high mutation frequencies detected (up to 24.51%), this study paves the way for regeneration of precisely mutated plants without the use of transgenesis.

CRISPR/Cas9 is a versatile and highly efficient genome editing tool used in many different plant species. In the present study, we compared the two most commonly used transient expression methods for genome editing, protoplast transfection and infiltration of Agrobacterium tumefaciens, to develop a rapid and efficient validation protocol. Vectors designed to target four different sites in the cabbage genome (two of which were model target genes and two related to the centromere-specific histone H3 ( CENH3 ) gene) were delivered to two red cabbage cultivars, ‘Huzaro F1’ and ‘Rebecca F1’. Targeted deep sequencing analysis showed that CRISPR/Cas9 vectors induced mutations in both cultivars at all target sites and revealed mutation rates of 1.27–11.95% for protoplast transfection and 0.07–14.42% for agroinfiltration. Our results demonstrate successful genome editing in cabbages with CRISPR/Cas9 by two different approaches for the rapid evaluation of genome editing efficiency. Key message Comparison of two different transient transformation methods for the validation of sgRNA in red cabbage ( B. oleracea var. capitata f. rubra ).

Dalmatian pyrethrum ( (Trevir.) Sch. Bip.), a plant species endemic to the east Adriatic coast, is used worldwide for production of the organic insecticide, pyrethrin. Most studies concerning Dalmatian pyrethrum have focused on its morphological and biochemical traits relevant for breeding. However, little is known about the chromosomal evolution and genome organization of this species. Our study aims are to identify, classify, and characterize repetitive DNA in the genome using clustering analysis of a low coverage genomic dataset. Repetitive DNA represents about 71.63% of the genome. exhibits linked 5S and 35S rDNA configuration (L-type). FISH reveals amplification of interstitial telomeric repeats (ITRs) in . Of the three newly identified satellite DNA families, TcSAT1 and TcSAT2 are located subterminally on most of chromosomes, while TcSAT3 family is located intercalary within the longer arm of two chromosome pairs. FISH reveals high levels of polymorphism of the TcSAT1 and TcSAT2 sites by comparative screening of 28 individuals. TcSAT2 is more variable than TcSAT1 regarding the number and position of FISH signals. Altogether, our data highlights the dynamic nature of DNA sequences associated with subtelomeres in and suggests that subtelomeres represent one of the most dynamic and rapidly evolving regions in eukaryotic genomes.

Testing inbred lines for their combining ability is, due to high numbers of line to line testing needed for determination of hybrid performance, the most limiting factor in the F1 hybrid breeding procedure. We propose a novel method of F1 hybrid breeding that enables evaluation of large number of line to line crosses for their hybrid performance. Inbred lines (preferably doubled haploid - DH) are produced from heterozygous populations, genotyped and maintained. A group of lines is inter-pollinated randomly and their progeny examined. To identify elite F1 hybrids, these individual plants are selected by their superior phenotypic characteristics. Finally using paternity testing only of selected hybrids, the origin of paternal lines is revealed. To predict the number of F1 offspring needed in relation to the number of inbred lines being inter-pollinated, a mathematical formula was developed. For instance, using this formula for the inter-pollination of 60 distinct lines, the probability of obtaining all descendants of paternal-parent lines in a maternal-parent row represented at least once is achieved with 420 F1 plants in a row (p = 0.95). In a practical experiment with white cabbage, DH lines were produced using microspore culture; plants were grown to maturity and genotyped at eight polymorphic SSR loci. Two groups of lines (36 and 33 lines per group) were inter-pollinated by two methods, either using cage pollination with bumblebees or using open pollination in isolated field. A total of 9,858 F1 plants were planted and based on their phenotypic characteristics 213 were selected as elite phenotypes. 99 of them were genetically diverse and 5 of them were selected as super elite. Selected plants were analysed by the same SSR markers and the paternal origin of selected F1 plants was determined. Out of 213 selected elite plants 48 were reciprocals thus exhibiting power of selection based on single plant. We demonstrate that this new approach to hybrid development is efficient in white cabbage and we propose breeders to test it in various vegetable and crop species. Moreover, some other aspects of the proposed technique need to be tested and verified both for practical and economic criteria.

A correction to this paper has been published: https://doi.org/10.1038/s41587-020-00800-8

Kohlrabi (Brassica oleracea var. gongylodes) cultivars Vienna Purple (VP) and Vienna White (VW) were tested for their ability of de novo organogenesis in vitro. Root, cotyledon, hypocotyl explants and intact seedlings were cultivated on Murashige and Skoog (MS) media supplemented with different cytokinins: benzyladenine (BA), thidiazuron (TDZ), trans- or cis-zeatin. All tested cytokinins, including cis-zeatin, induced shoot regeneration from hypocotyl explants and intact seedlings, with seedlings being most successful for regeneration efficiency and viability of regenerated shoots in both cultivars. The highest frequency of shoot regeneration was achieved on MS with BA (60 %) or TDZ (50 %) for VP; and with BA (50 %), TDZ (47.5 %) or transZ (37.5 %) for VW. Measurements of the endogenous cytokinin and indole-3-acetic acid (IAA) contents in both hypocotyl explants and seedlings with regenerated shoots (HRSs and SRSs) suggested that the observed differences in organogenic response between these two types of explants were related to their cytokinin and IAA contents. HRSs generally exhibited elevated amounts of total cytokinins, while SRSs displayed a higher IAA/bioactive cytokinins ratio. Shoots regenerated from seedlings were further successfully multiplicated on a medium supplemented with BA (0.5 mg L−1). The rooting potential of multiplicated shoots was tested on media supplemented with 2 or 4 mg L−1 indole-3-butyric acid (IBA), with the higher concentration of IBA leading to more efficient rooting. Rooted plantlets were successfully planted into soil and flow cytometric analysis did not reveal ploidy variations, indicating that the described protocol is fast and efficient for kohlrabi regeneration.

A successful in vitro Agrobacterium-mediated transformation protocol was developed for Mimulus aurantiacus, a model species for ecological and evolutionary genetics and a promising ornamental plant. Three binary vectors were tested, each containing the hptII selectable marker gene and one of the reporter genes: gusA, EGFP or ZsGreen, all of them under CaMV 35S promoter. Genetic transformation was achieved through 4 days of co-cultivation of leaf, petiole and hypocotyl explants with Agrobacterium tumefaciens strain LBA 4404. Explants produced transformed callus tissue on solid modified Murashige and Skoog medium supplemented with 1 mg L−1 6-benzylaminopurine, 0.5 mg L−1 1-naphthaleneacetic acid, 30 g L−1 sucrose and 20 or 50 mg L−1 hygromycin B. All three reporter genes were expressed in callus tissue but the intensity of expression gradually decreased during further plant development. The new reporter gene ZsGreen proved suitable for plant transformation experiments since very intense and bright fluorescence was detected. Out of 1,760 co-cultured explants, 110 plants were regenerated and all of them were found to be PCR positive for the selection and/or reporter genes. Chemiluminescent Southern blot analysis revealed that 91 % of the regenerated plants (100 T0 plants) contained T-DNA integrated in their genome. Transformation efficiency varied from 1.4 to 23.3 % for hypocotyl and petiole explants, respectively. Integration of some backbone sequences in plant genomes was confirmed in 75.3 % of T0 plants. Using this protocol, stable transformants expressing selectable marker gene hptII and one of the reporter genes (gusA, ZsGreen or EGFP) were obtained in 4–5 months.

Higher concentrations of anthocyanins in vegetables are important for attractive appearance and may offer health benefits for consumers. The red color of onion ( Allium cepa ) bulbs is due primarily to the accumulation of anthocyanins. The goal of this study was to identify chromosome regions that significantly affect concentrations of anthocyanins and soluble solids in onion bulbs. Segregating haploid plants from the cross of yellow (OH1) and red (5225) inbreds were asexually propagated and bulbs were produced in replicated trials across three environments. Concentrations of soluble solids were measured at 30 days after harvest and quantitative analyses revealed a significant region on chromosome 5. Analyses using a binary model for segregation of red versus yellow bulbs revealed a significant region on chromosome 7 and two regions linked in repulsion phase on chromosome 4. These results are consistent with the complementary two-locus model previously proposed to control red versus yellow bulb colors in onion. The region on chromosome 7 mapped to the same location as the R locus, and the regions on chromosome 4 may correspond to the L and L2 loci. The intensity of red bulb color was assessed visually by a panel of evaluators and by amounts of anthocyanins [peonidin 3-glucoside and cyanidin 3-(6″-malonoyl-laminaribioside)] measured by high-performance liquid chromatography. Quantitative analyses using a normal model revealed significant quantitative trait loci on chromosomes 1, 4 and 8 affecting anthocyanin concentrations, and yellow onion contributed beneficial genetic variation to enhance red bulb color. Significant correlations were observed between these anthocyanin concentrations and panel scores, indicating that visual selection should be effective for increasing anthocyanin levels in onion bulbs. These selected populations may be more attractive to consumers, potentially provide health benefits from increased anthocyanin consumption, and be a source of natural colorants.

Protocols leading to the development of doubled haploid (DH) lines by microspore culture are widely used in white cabbage ( var. L.), but efficiency varies according to the cultivar and induction procedure. Forty different genotypes consisting of F1 cultivars and their crosses with responsive doubled haploid lines were tested to evaluate the androgenic response. In total, 20,032 embryos were produced. On average, the haploid induction response of F1 cultivars was 7.0 embryos/Petri dish, but the average of these hybrids crossed to responsive DH lines was 26.6 embryos/Petri dish. In seven reciprocal crosses, a difference was observed in just one, meaning that the maternal effect probably has a minor influence on haploid embryogenesis in cabbage. Addition of 0.02% activated charcoal (AC) to the induction media increased embryo formation in several low-responsive genotypes, but its effect on embryo formation of high-responsive genotypes was predominantly negative, although larger embryos were formed on media containing AC than without AC. Further development into plantlets was tested by two procedures. Formed embryos were either transferred directly to regeneration medium or treated with abscisic acid and desiccated for 4 weeks. Regrowth and further development reached on average 15.5 and 57.6%, for the first and second procedures, respectively. Plantlets developed by direct transfer often exhibited abnormal development or hyperhydricity, unlike the desiccated embryos. Spontaneous diploidisation of embryos reached 42.5% in total and was not affected by AC added to the induction media.

V sestavku je kratko opisan pomen genskih bank od ustanovitve prvih nacionalnih ustanov do trenutnega stanja na tem področju. Poudarjen je tako pomen ohranjanja genskih virov za napredek kmetijstva kot tudi pomen genskih virov kot kulturne dediščine človeštva. Kratko je predstavljen pogled na zakonodajo, ki je nastala z uveljavitvijo mednarodne pogodbe o genskih virih.