Mining plant diversity: Gerbera as a model system for plant developmental and biosynthetic research

Phenotypic Variation in Flower Color and Morphology in the Gerbera (Gerbera hybrida) F1 Hybrid Population and Their Association with EST-SSR Markers

Gerbera (Gerbera hybrida) is a widely cultivated ornamental plant. However, its genetic improvement is limited by the lack of genetic analysis and molecular markers for traits. In this study, we analyzed the phenotypic and genotypic variation of 140 F1 progeny from two gerbera varieties with different flower types and colors. We evaluated the flower's morphology, color, and pigment content of the F1 population and performed cluster principal component analysis (PCA) and correlation analysis. The results showed that the main ornamental traits of the hybrid progeny varied greatly. The segregation ratios of single and double flowers and ligulate and split ray florets were both 1:1. The flower colors of the F1 progeny were mainly red and purple-red, similar to the male parent's color. Furthermore, we conducted a genetic analysis of the hybrid progeny using EST-SSR markers and performed association analysis with phenotypic traits. We identified 2, 2, 3, 1, and 2 loci to be associated with peduncle length (PL), ray floret length (RFL), and outer ray floret; the level of apex relative to the top of involucre (LAI); outer corolla lips (OCL); and the b* of ray floret color, respectively. Our results reveal the genetic patterns of important ornamental traits and provide a theoretical basis and practical tools for gerbera genetic breeding.

Integrative Analysis of miRNAs and Their Targets Involved in Ray Floret Growth in Gerbera hybrida

MicroRNAs (miRNAs) are involved in regulating many aspects of plant growth and development at the post-transcriptional level. Gerbera (Gerbera hybrida) is an important ornamental crop. However, the role of miRNAs in the growth and development of gerbera is still unclear. In this study, we used high-throughput sequencing to analyze the expression profiles of miRNAs in ray floret during inflorescence opening. A total of 164 miRNAs were obtained, comprising 24 conserved miRNAs and 140 novel miRNAs. Ten conserved and 15 novel miRNAs were differentially expressed during ray floret growth, and 607 differentially expressed target genes of these differentially expressed miRNAs were identified using psRNATarget. We performed a comprehensive analysis of the expression profiles of the miRNAs and their targets. The changes in expression of five miRNAs (ghy-miR156, ghy-miR164, ghy-miRn24, ghy-miRn75 and ghy-miRn133) were inversely correlated with the changes in expression of their eight target genes. The miRNA cleavage sites in candidate target gene mRNAs were determined using 5′-RLM-RACE. Several miRNA-mRNA pairs were predicted to regulate ray floret growth and anthocyanin biosynthesis. In conclusion, the results of small RNA sequencing provide valuable information to reveal the mechanisms of miRNA-mediated ray floret growth and anthocyanin accumulation in gerbera.

Classification and Association Analysis of Gerbera (Gerbera hybrida) Flower Color Traits

Floral color plays a crucial role in plant life such as plant-pollinator interactions and modifying the abiotic environment of reproductive structures. In the current study, 123 gerbera accessions were divided into six color groups (white, yellow, orange, pink, red, and purple), based on Royal Horticultural Society Color Chart calibration and colorimeter measurement. Partial least squares discriminant analysis showed that the white group was mainly affected by L* value, a* value, C value, and total anthocyanin contents, while the yellow group was positively correlated with L* value, b* value, and total anthocyanin contents. Similarly, the orange group was mainly affected by b* value and total carotenoid contents, whereas the pink group was positively correlated with L* and h values. Furthermore, the red group was affected by L* value, a* value, C value, and total anthocyanin contents, whilst the purple group was mainly distributed by L* value, a* value, b* value, and total anthocyanin contents. Based on 'Jin Xiang' transcriptome data, 14,106 expressed sequence tag (EST)-SSR markers were identified and 48 pairs of primers (19 newly developed primers) were screened. Population genetic structure, neighbor-joining clustering, and principal coordinate analysis showed that 123 gerbera accessions could be divided into two groups. EST-SSR-based association analysis showed that 1, 1, 2, 1, 1, 2, and 1 significant loci were related to L*, a*, b*, C, and h, total carotenoid, and total anthocyanin contents, respectively. These results provide an important reference for flower color classification and genetic improvement of gerbera.

Picloram-induced enhanced callus-mediated regeneration, acclimatization, and genetic clonality assessment of gerbera

Background

Gerbera jamesonii Bolus ex Hooker f. (African daisy) is listed among the top five most important ornamental plants in the global floricultural industry. To satisfy its demand, the floriculture industry relies on reproducible and effective propagation protocol while retaining the genetic uniformity of G. jamesonii. The present study, for the first time, reports the potential of picloram for enhanced induction of organogenic calli from leaves of G. jamesonii and its high-frequency indirect regeneration.

Results

The fastest induction of calli with maximum fresh and dry weight was recorded in the Murashige and Skoog (MS) semisolid medium supplemented with 1 mg/l picloram. In addition, callus induction was observed in 2,4-dichlorophenoxy acetic acid- and α-napthaleneaceticacid-supplemented media but with delayed response and reduced fresh and dry weight. The proliferated calli were transferred to shoot induction media containing MS salt and 0.5–1 mg/l N⁶-benzylaminopurine, kinetin, or thidiazuron. A mean number of ~6 shoots per callus were developed after 5 days of culture in the MS medium supplemented with 1 mg/l kinetin, with a mean length of 5.2 cm. Successful rooting of shoots was achieved in the MS medium fortified with 1.5 mg/l indole-3-acetic acid, wherein the earliest root initiation (~5 days), as well as the maximum number (~9) and length (~4.8 cm) of roots, were recorded. Complete plantlets were primarily acclimatized in sand before being transferred to a mixed substrate (of soil, sand, tea leaf waste, and cow urine) that secured >90% survival and further growth of the plantlets. Eventually, clonal fidelity of the in vitro regenerants assessed via inter-simple sequence repeats (ISSR) primers exhibited a monomorphic banding patterns that suggested genetic integrity within the plantlets as well as with their mother plant.

Conclusions

The results of the present study should be of interest for commercial propagation and mutagenesis- as well as genetic transformation-related research.

Tetraketide α-pyrone reductases in sporopollenin synthesis pathway in Gerbera hybrida: diversification of the minor function

The structurally robust biopolymer sporopollenin is the major constituent of the exine layer of pollen wall and plays a vital role in plant reproductive success. The sporopollenin precursors are synthesized through an ancient polyketide biosynthetic pathway consisting of a series of anther-specific enzymes that are widely present in all land plant lineages. Tetraketide α-pyrone reductase 1 (TKPR1) and TKPR2 are two reductases catalyzing the final reduction of the carbonyl group of the polyketide synthase-synthesized tetraketide intermediates to hydroxylated α-pyrone compounds, important precursors of sporopollenin. In contrast to the functional conservation of many sporopollenin biosynthesis associated genes confirmed in diverse plant species, TKPR2's role has been addressed only in Arabidopsis, where it plays a minor role in sporopollenin biosynthesis. We identified in gerbera two non-anther-specific orthologues of AtTKPR2, Gerbera reductase 1 (GRED1) and GRED2. Their dramatically expanded expression pattern implies involvement in pathways outside of the sporopollenin pathway. In this study, we show that GRED1 and GRED2 are still involved in sporopollenin biosynthesis with a similar secondary role as AtTKPR2 in Arabidopsis. We further show that this secondary role does not relate to the promoter of the gene, AtTKPR2 cannot rescue pollen development in Arabidopsis even when controlled by the AtTKPR1 promoter. We also identified the gerbera orthologue of AtTKPR1, GTKPR1, and characterized its crucial role in gerbera pollen development. GTKPR1 is the predominant TKPR in gerbera pollen wall formation, in contrast to the minor roles GRED1 and GRED2. GTKPR1 is in fact an excellent target for engineering male-sterile gerbera cultivars in horticultural plant breeding.

Polyketide Derivatives in the Resistance of Gerbera hybrida to Powdery Mildew

Powdery mildew is a common disease affecting the commercial production of gerbera flowers (Gerbera hybrida, Asteraceae). Some varieties show a certain degree of resistance to it. Our objective was to identify biomarkers of resistance to powdery mildew using an ¹H nuclear magnetic resonance spectroscopy and chemometrics approach in a complex, fully factorial experiment to suggest a target for selection and breeding. Resistant varieties were found to differ from those that were susceptible in the metabolites of the polyketide pathway, such as gerberin, parasorboside, and gerberinside. A new compound probably involved in resistance, 5-hydroxyhexanoic acid 3-O-β-D-glucoside, was described for the first time. A decision tree model was built to distinguish resistant varieties, with an accuracy of 57.7%, sensitivity of 72%, and specificity of 44.44% in an independent test. Our results suggest the mechanism of resistance to powdery mildew in gerbera and provide a potential tool for resistance screening in breeding programs.

Sequencing and analysis of gerbera daisy leaf transcriptomes reveal disease resistance and susceptibility genes differentially expressed and associated with powdery mildew resistance

BACKGROUND

RNA sequencing has been widely used to profile genome-wide gene expression and identify candidate genes controlling disease resistance and other important traits in plants. Gerbera daisy is one of the most important flowers in the global floricultural trade, and powdery mildew (PM) is the most important disease of gerbera. Genetic improvement of gerbera PM resistance has become a crucial goal in gerbera breeding. A better understanding of the genetic control of gerbera resistance to PM can expedite the development of PM-resistant cultivars.

RESULTS

The objectives of this study were to identify gerbera genotypes with contrasting phenotypes in PM resistance and sequence and analyze their leaf transcriptomes to identify disease resistance and susceptibility genes differentially expressed and associated with PM resistance. An additional objective was to identify SNPs and SSRs for use in future genetic studies. We identified two gerbera genotypes, UFGE 4033 and 06-245-03, that were resistant and susceptible to PM, respectively. De novo assembly of their leaf transcriptomes using four complementary pipelines resulted in 145,348 transcripts with a N50 of 1124 bp, of which 67,312 transcripts contained open reading frames and 48,268 were expressed in both genotypes. A total of 494 transcripts were likely involved in disease resistance, and 17 and 24 transcripts were up- and down-regulated, respectively, in UFGE 4033 compared to 06-245-03. These gerbera disease resistance transcripts were most similar to the NBS-LRR class of plant resistance genes conferring resistance to various pathogens in plants. Four disease susceptibility transcripts (MLO-like) were expressed only or highly expressed in 06-245-03, offering excellent candidate targets for gene editing for PM resistance in gerbera. A total of 449,897 SNPs and 19,393 SSRs were revealed in the gerbera transcriptomes, which can be a valuable resource for developing new molecular markers.

CONCLUSION

This study represents the first transcriptomic analysis of gerbera PM resistance, a highly important yet complex trait in a globally important floral crop. The differentially expressed disease resistance and susceptibility transcripts identified provide excellent targets for development of molecular markers and genetic maps, cloning of disease resistance genes, or targeted mutagenesis of disease susceptibility genes for PM resistance in gerbera.

The core regulatory networks and hub genes regulating flower development in Chrysanthemum morifolium

The study has facilitated important insights into the regulatory networks involved in flower development in chrysanthemum (Asteraceae), and is informative with respect to the mechanism of flower shape determination. Chrysanthemum morifolium, valued as an ornamental species given the diversity of its inflorescence form, is viewed as a model for understanding flower development in the Asteraceae. Yet, the underlying regulatory networks remain largely unexplored. Here, a transcriptomic survey of the Chrysanthemum morifolium variety 'Jinba' was undertaken to uncover the global gene expression profiles and identify the modules of co-transcribed genes associated with flower development. The weighted gene coexpression network analysis revealed important networks and hub genes including ray floret petals-specific coexpression network, disc floret petals-specific network, B and E class genes involved network and CYC2 genes network. Three ray floret petal-specific hub genes were also strongly transcribed in the ray florets of a selection of six diverse varieties and especially so in those which form ligulate ray floret petals. CmCYC2c was strongly transcribed in the distal and lateral regions of the ray floret petals, and also, along with CmCYC2d, in the tubular ray florets. Furthermore, CmOFP, belonging to the family of ovate proteins, was identified in the CYC2 genes network. CmOFP can interact with CmCYC2d that physically interact with CmCYC2c. This work provides important insights into the regulatory networks involved in flower development in chrysanthemum, and is informative with respect to the mechanistic basis of the regulation of flower shape.

Induction of powdery mildew resistance in gerbera (Gerbera jamesonii) through gamma irradiation

In this study, the effect of gamma irradiation in inducing resistance/tolerance towards powdery mildew disease was investigated in Gerbera jamesonii cv. 'Harley'. In vitro shoot cultures were established through capitulum explants on Murashige and Skoog medium supplemented with 22.2 µM 6-benzyladenine (BA) and 2.53 µM indole acetic acid (IAA), followed by gamma irradiation of regenerated shoots (3-5 cm). Activity of four antioxidant enzymes i.e. superoxide dismutase, ascorbate peroxidase, catalase and glutathione reductase increased significantly as compared to the control and reached to highest level at the most stringent doses of mutagen. Ninety randomly selected irradiated plants (6 months old) and 100 control plants were inoculated with fungal conidial suspension, to screen for tolerance/resistance against powdery mildew. The severity of the disease was recorded on 0-4 scale with '0' indicating highly resistant; '1' indicating resistant; '2' indicating medium resistance; '3' indicating susceptible and '4' indicating highly susceptible. Three plants (3.33%) irradiated with 5 Gy were found to be tolerant to powdery mildew as these plants showed slight and delayed development of fungal colonies on the leaves. The random amplified polymorphic DNA characterization showed that the irradiated plants had DNA patterns that were different from the control and mother plants.

Application of CRISPR/Cas9 to Tragopogon (Asteraceae), an evolutionary model for the study of polyploidy

Tragopogon (Asteraceae) is an excellent natural system for studies of recent polyploidy. Development of an efficient CRISPR/Cas9-based genome editing platform in Tragopogon will facilitate novel studies of the genetic consequences of polyploidy. Here, we report our initial results of developing CRISPR/Cas9 in Tragopogon. We have established a feasible tissue culture and transformation protocol for Tragopogon. Through protoplast transient assays, use of the TragCRISPR system (i.e. the CRISPR/Cas9 system adapted for Tragopogon) was capable of introducing site-specific mutations in Tragopogon protoplasts. Agrobacterium-mediated transformation with Cas9-sgRNA constructs targeting the phytoene desaturase gene (TraPDS) was implemented in this model polyploid system. Sequencing of PCR amplicons from the target regions indicated simultaneous mutations of two alleles and four alleles of TraPDS in albino shoots from Tragopogon porrifolius (2x) and Tragopogon mirus (4x), respectively. The average proportions of successfully transformed calli with the albino phenotype were 87% and 78% in the diploid and polyploid, respectively. This appears to be the first demonstration of CRISPR/Cas9-based genome editing in any naturally formed neopolyploid system. Although a more efficient tissue culture system should be developed in Tragopogon, application of a robust CRISPR/Cas9 system will permit unique studies of biased fractionation, the gene-balance hypothesis and cytonuclear interactions in polyploids. In addition, the CRISPR/Cas9 platform enables investigations of those genes involved in phenotypic changes in polyploids and will also facilitate novel functional biology studies in Asteraceae. Our workflow provides a guide for applying CRISPR/Cas9 to other nongenetic model plant systems.

GhWIP2, a WIP zinc finger protein, suppresses cell expansion in Gerbera hybrida by mediating crosstalk between gibberellin, abscisic acid, and auxin

Cell expansion is a key determinant for the final size and shape of plant organ, and is regulated by various phytohormones. Zinc finger proteins (ZFPs) consist of a superfamily involved in multiple aspects of organ morphogenesis. However, little is known about WIP-type ZFP function in phytohormone-mediated organ growth. Using reverse genetics, RNA-seq and phytohormone quantification, we elucidated the role of a new WIP-type ZFP from Gerbera hybrida, GhWIP2, in controlling organ growth via regulation of cell expansion. GhWIP2 localizes to the nucleus and acts as a transcriptional repressor. Constitutive overexpression of GhWIP2 (GhWIP2OE) in both Gerbera and Arabidopsis thaliana caused major developmental defects associated with cell expansion, including dwarfism, short petals, scapes, and petioles. Furthermore, GhWIP2OE plants were hypersensitive to GA, but not to ABA, and showed a reduction in endogenous GA and auxin, but not ABA concentrations. Consistent with these observations, RNA-seq analysis revealed that genes involved in GA and auxin signaling were down-regulated, while those involved in ABA signaling were up-regulated in GhWIP2OE plants. Our findings suggest that GhWIP2 acts as a transcriptional repressor, suppressing cell expansion during organ growth by modulating crosstalk between GA, ABA, and auxin.

Flower heads in Asteraceae-recruitment of conserved developmental regulators to control the flower-like inflorescence architecture

Inflorescences in the Asteraceae plant family, flower heads, or capitula, mimic single flowers but are highly compressed structures composed of multiple flowers. This transference of a flower-like appearance into an inflorescence level is considered as the key innovation for the rapid tribal radiation of Asteraceae. Recent molecular data indicate that Asteraceae flower heads resemble single flowers not only morphologically but also at molecular level. We summarize this data giving examples of how rewiring of conserved floral regulators have led to evolution of morphological innovations in Asteraceae. Functional diversification of the highly conserved flower meristem identity regulator LEAFY has shown a major role in the evolution of the capitulum architecture. Furthermore, gene duplication and subsequent sub- and neofunctionalization of SEPALLATA- and CYCLOIDEA-like genes in Asteraceae have been shown to contribute to meristem determinacy, as well as flower type differentiation-key traits that specify this large family. Future challenge is to integrate genomic, as well as evolutionary developmental studies in a wider selection of Asteraceae species to understand the detailed gene regulatory networks behind the elaborate inflorescence architecture, and to promote our understanding of how changes in regulatory mechanisms shape development.

Two polyketide synthases are necessary for 4-hydroxy-5-methylcoumarin biosynthesis in Gerbera hybrida

Gerbera (Gerbera hybrida) is an economically important ornamental species and a model plant of the Asteraceae family for flower development and secondary metabolism. Gerberin and parasorboside, two bitter tasting glucosidic lactones, are produced in high amounts in nearly all gerbera tissues. Gerbera and its close relatives also produce a rare coumarin, 4-hydroxy-5-methylcoumarin (HMC). Unlike most coumarins, 5-methylcoumarins have been suggested to be derived through the acetate-malonate pathway. All of these polyketide-derived glucosylated molecules are considered to have a role in defense against herbivores and phytopathogens in gerbera. Gerbera expresses three genes encoding 2-pyrone synthases (G2PS1-3). The enzymes are chalcone synthase-like polyketide synthases with altered starter substrate specificity. We have shown previously that G2PS1 is responsible for the synthesis of 4-hydroxy-6-methyl-2-pyrone (triacetolactone), a putative precursor of gerberin and parasorboside. Here we show that polyketide synthases G2PS2 and G2PS3 are necessary for the biosynthesis of HMC in gerbera, and that a reductase enzyme is likely required to complete the pathway to HMC. G2PS2 is expressed in the leaf blade and inflorescences of gerbera, while G2PS3 is strictly root specific. Heterologous expression of G2PS2 or G2PS3 in tobacco leads to the formation of 4,7-dihydroxy-5-methylcoumarin, apparently an unreduced precursor of HMC, while ectopic expression in gerbera leads to HMC formation in tissues where nontransgenic tissue does not express the genes and does not accumulate the compound. Using protein modelling and site-directed mutagenesis we identified the residues I203 and T344 in G2PS2 and G2PS3 to be critical for pentaketide synthase activity.

Ancient WGD events as drivers of key innovations in angiosperms

Polyploidy, or whole-genome duplication (WGD), is a ubiquitous feature of plant genomes, contributing to variation in both genome size and gene content. Although polyploidy has occurred in all major clades of land plants, it is most frequent in angiosperms. Following a WGD in the common ancestor of all extant angiosperms, a complex pattern of both ancient and recent polyploidy is evident across angiosperm phylogeny. In several cases, ancient WGDs are associated with increased rates of species diversification. For example, a WGD in the common ancestor of Asteraceae, the largest family of angiosperms with ∼25000 species, is statistically linked to a shift in species diversification; several other old WGDs are followed by increased diversification after a 'lag' of up to three nodes. WGD may thus lead to a genomic combination that generates evolutionary novelty and may serve as a catalyst for diversification. In this paper, we explore possible links between WGD, the origin of novelty, and key innovations and propose a research path forward.

Transcriptome Analysis of Gerbera hybrida Including in silico Confirmation of Defense Genes Found

For the ornamental crop Gerbera hybrida, breeding at the moment is done using conventional methods. As this has drawbacks in breeding speed and efficiency, especially for complex traits like disease resistance, we set out to develop genomic resources. The leaf and flower bud transcriptomes of four parents, used to generate two gerbera populations, were sequenced using Illumina paired-end sequencing. In total, 36,770 contigs with an average length of 1397 bp were generated and these have been the starting point for SNP identification and annotation. The consensus contig sequences were used to map reads of individual parents, to identify genotype specific SNPs, and to assess the presence of common SNPs between genotypes. Comparison with the non-redundant protein database (nr) showed that 29,146 contigs gave BLAST hits. Of sequences with blast results, 73.3% obtained a clear gene ontology (GO) annotation. EST contigs coding for enzymes were found in Kyoto Encyclopedia of Genes and Genomes maps (KEGG). Through, these annotated data and KEGG molecular interaction network, transcripts associated with the phenylpropanoid metabolism, other secondary metabolite biosynthesis pathways, phytohormone biosynthesis and signal transduction were analyzed in more detail. Identifying genes involved in these processes could provide genetic and genomic resources for studying the mechanism of disease resistance in gerbera.

Occupational allergy to flowers: immunoblot analysis of allergens in freesia, gerbera and chrysanthemum pollen

High exposure to pollen from ornamental flowers can induce an IgE-mediated occupational allergy in florists and horticulture workers. We investigated IgE-binding antigens in chrysanthemum, freesia and gerbera pollen by immunoblot analysis and analysed the cross-reactivity of these pollen with birch, grass and mugwort pollen. In immunoblots with chrysanthemum pollen, major IgE-binding structures were seen with a molecular weight (MW) of approximately 25, 45 and 65 kD. In the immunoblots with freesia pollen, IgE from freesia pollen was directed against two proteins with an MW of approximately 15 kD. Most sera showed IgE binding to an approximately 15 kD band in gerbera pollen; with some sera additional bands were seen in the range of 30-50 kD. IgE binding to chrysanthemum pollen was inhibited by mugwort pollen only, whereas IgE binding to freesia pollen was suppressed by birch, grass and mugwort pollen. The inhibitory activity of birch and grass pollen extract on IgE binding to gerbera pollen extract was serum dependent and ranged from no inhibition to complete inhibition. Occupational exposure to many different flowers induced IgE against all three types of pollen. Exposure in greenhouses to gerbera flowers elicited mainly IgE against gerbera pollen. Mugwort pollen extract inhibited IgE binding to pollen from all three flowers.

Gerbera micropropagation

Gerbera jamesonii (gerbera) is an important cut-flower in the global floricultural industry. Micropropagation is the main system used to clonally propagate gerbera in vitro resulting in the production of millions of plantlets each year. Numerous types of explants and protocols for micropropagation have been established and used for gerbera. Shoot tips are the commonly used explant while adventitious shoot induction from the capitulum is also a popular method. Most papers in the literature have focused on testing the influence of different types and combinations of plant growth regulators with the aim of improving the regeneration and multiplication stage of one or few cultivars. Genotype is one of the most influential factors on the response of gerbera in vitro. Despite this, no successful universal protocol has yet been developed for multiple cultivars, limiting the usefulness of current protocols for commercial biotechnology labs. Slow-growing endogenous bacteria are one of the most important problems in gerbera micropropagation but require more studies on control and prevention. Individual shoots are normally easy to root, usually in excess of 90% of plantlets, but the acclimatization stage requires improvements and new technologies to increase the survival of plants. Epigenetic variations in micropropagated gerbera are frequently observed only with high concentrations of cytokinins in the culture medium but somaclonal variation is rare.

[Evolution and development of the flower]

The appearance of the angiosperm flower has been an important morphological innovation in plant evolution and is thought to be, at least in part, responsible for the evolutionary success of flowering plants. Through studying and comparing the molecular basis of flower development in different model species, we can gain insights into the diversification of developmental networks that underlie the vast array of angiosperm floral morphologies. Floral development is controlled by several genes among which MADS-box genes play a crucial role as homeotic genes. Indeed, the evolution of the MADS-box transcription factor family appears to have played a pivotal role in the development of flower diversity.

GT1-7 cell-based cytoxicity screening assay on 96-well microplates as a platform for the safety assessment of genetically modified Gerbera hybrida extracts

In this investigation, a GT1-7 cell-based cytotoxicity screening assay in 96-well microplates was set up. The assay, using propidium iodide fluorescence, was proven to be reliable, with good quality (Z' = 0.51) and low plate-to-plate and day-to-day variations. Further on, a library containing extracts from 227 genetic modification (GM) Gerbera hybrida and 42 Gerbera varieties was screened; however, no differences between them were found. Based on these findings, we propose the use of the current assay within the first-tier screening studies of large collections. Also, these results provide valuable information for GM Gerbera risk-assessment purposes and offer a model for the toxicity cell-based screening of GM crops.

Transcriptional analysis of petal organogenesis in Gerbera hybrida

Understanding of the molecular interplay, which determines early steps of flower formation has grown considerably during last years. In contrast, genetic actions responsible for how flower organs acquire their size and shape at later phases of organogenesis are still poorly understood. We have exploited the large and anatomically simple Gerbera (Gerbera hybrida var. Terra regina) ray flower petals to describe transcriptional changes during organogenesis. Gerbera 9 K cDNA microarray was utilized to profile gene expression at six different developmental stages of petal organogenesis, at the earliest stage expansion of petals is starting and at the latest stage petals have reached their final size and shape. Genes potentially participating in petal opening were identified based on the similarity in expression with a known marker gene. Our results showed characteristic sets of genes expressed during the cell division and cell expansion phases of petal development. Interestingly, there was a transition stage during which neither cell division nor cell expansion marker genes were abundantly expressed. Moreover, constitutive expression of late petal specific genes indicates that they participate in petal organogenesis throughout the development and they are not involved in stage specific switch points.