Renate Müller

Genome-Wide Analysis of the Arabidopsis Leaf Transcriptome Reveals Interaction of Phosphate and Sugar Metabolism

Global gene expression was analyzed in Arabidopsis (Arabidopsis thaliana) by microarrays comprising 21,500 genes. Leaf segments derived from phosphorus (P)-starved and P-replenished plants were incubated with or without sucrose (Suc) to obtain tissues with contrasting combinations of P and carbohydrate levels. Transcript profiling revealed the influence of the two factors individually and the interactions between P- and sugar-dependent gene regulation. A large number of gene transcripts changed more than 2-fold: In response to P starvation, 171 genes were induced and 16 repressed, whereas Suc incubation resulted in 337 induced and 307 repressed genes. A number of new candidate genes involved in P acquisition were discovered. In addition, several putative transcription factors and signaling proteins of P sensing were disclosed. Several genes previously identified to be sugar responsive were also regulated by P starvation and known P-responsive genes were sugar inducible. Nearly 150 genes were synergistically or antagonistically regulated by the two factors. These genes exhibit more prominent or contrasting regulation in response to Suc and P in combination than expected from the effect of the two factors individually. The genes exhibiting interactions form three main clusters with different response patterns and functionality of genes. One cluster (cluster 1) most likely represents a regulatory program to support increased growth and development when both P and carbohydrates are ample. Another cluster (cluster 3) represents genes induced to alleviate P starvation and these are further induced by carbohydrate accumulation. Thus, interactions between P and Suc reveal two different signaling programs and novel interactions in gene regulation in response to environmental factors. cis-Regulatory elements were analyzed for each factor and for interaction clusters. PHR1 binding sites were more frequent in promoters of P-regulated genes as compared to the entire Arabidopsis genome, and E2F and PHR1 binding sites were more frequent in interaction clusters 1 and 3, respectively.

Characterization of an ethylene receptor family with differential expression in rose (Rosa hybrida L.) flowers

Abstract To analyze differences in flower longevity and ethylene sensitivity, we isolated Rosa hybrida gene fragments with sequence similarity to the Arabidopsis thaliana ethylene receptor gene-family. A rose gene (RhETR1) highly similar to AtERS1 had been previously sequenced. Here, we report the isolation of three additional partial rose genes (RhETR2–4) belonging to different sub-groups of ethylene receptor genes. RhETR2 clusters with AtETR1, RhETR4 with AtERS1 and RhETR1, whereas RhETR3 shows high sequence similarity to AtETR2 and AtERS2. Expression analysis of RhETR2 and RhETR3 revealed that they are differentially expressed. RhETR2 is expressed at a constitutive level throughout flower development whereas RhETR3 expression increases in senescing flowers of the cultivar Bronze which has a short floral life while it remains at low levels in the long-lasting flowers of the cultivar Vanilla. Expression of both genes was increased by ABA and ethylene treatment, but transcript abundance differed between rose cultivars with different postharvest performance. These results indicate that differences in flower life among rose cultivars could be due to differences in receptor levels.

Can ornamental potted plants remove volatile organic compounds from indoor air? — a review

Volatile organic compounds (VOCs) are found in indoor air, and many of these can affect human health (e.g. formaldehyde and benzene are carcinogenic). Plants affect the levels of VOCs in indoor environments, thus they represent a potential green solution for improving indoor air quality that at the same time can improve human health. This article reviews scientific studies of plants’ ability to remove VOCs from indoor air. The focus of the review is on pathways of VOC removal by the plants and factors affecting the efficiency and rate of VOC removal by plants. Laboratory based studies indicate that plant induced removal of VOCs is a combination of direct (e.g. absorption) and indirect (e.g. biotransformation by microorganisms) mechanisms. They also demonstrate that plants’ rate of reducing the level of VOCs is influenced by a number of factors such as plant species, light intensity and VOC concentration. For instance, an increase in light intensity has in some studies been shown to lead to an increase in removal of a pollutant. Studies conducted in real-life settings such as offices and homes are few and show mixed results.

Isolation and characterization of four somatic embryogenesis receptor-like kinase (RhSERK) genes from miniature potted rose (Rosa hybrida cv. Linda)

The isolation and expression analysis of four partial gene sequences from rose (Rosa hybrida cv. Linda) belonging to the receptor-like kinase gene superfamily are reported. These genes have been designated RhSERK1 to RhSERK4 (Accession No. EF631967 to EF631970) as they exhibit high sequence identities with genes from the somatic embryogenesis receptor-like kinase (SERK) family in other plant species. The RhSERK genes are differentially expressed in non-embryogenic callus, embryogenic callus, mature somatic embryos and a range of tissues from intact plants, indicating a broad role in plant growth and development. However, the expressions of RhSERK3 and RhSERK4 were approximately fivefold higher in embryogenic callus than in non-embryogenic callus, and they are even higher when compared to tissues from intact plants. In addition, RhSERK4 expression was approximately eightfold higher in somatic embryos than in embryogenic callus. These results suggest that the expression pattern of RhSERK3 and RhSERK4 may be used as a marker of somatic embryogenesis.

Production of compact plants by overexpression of AtSHI in the ornamental Kalanchoë

Growth retardation is an important breeding aim and an essential part of horticultural plant production. Here, the potential of transferring the Arabidopsis short internode (shi) mutant phenotype was explored by expressing the AtSHI gene in the popular ornamental plant Kalanchoë. A 35S-AtSHI construct was produced and transferred into eight genetically different cultivars of Kalanchoë by Agrobacterium tumefaciens. The resulting transgenic plants showed dwarfing phenotypes like reduced plant height and diameter, and also more compact inflorescences, as a result of increased vegetative height. The shi phenotype was stable over more than five vegetative subcultivations. Compared with Arabidopsis, the ectopic expression of AtSHI in Kalanchoë showed several differences. None of the Kalanchoë SHI-lines exhibited alterations in leaf colour or morphology, and most lines were not delayed in flowering. Moreover, continuous treatment of lines delayed in flowering with low concentrations of gibberellins completely restored the time of flowering. These features are very important as a delay in flowering would increase plant production costs significantly. The effect of expression controlled by the native Arabidopsis SHI promoter was also investigated in transgenic Kalanchoë and resulted in plants with a longer flowering period. Two AtSHI like genes were identified in Kalanchoë indicating a widespread presence of this transcription factor. These findings are important because they suggest that transformation with the AtSHI gene could be applied to several species as a tool for growth retardation, and that this approach could substitute the use of conventional chemical growth regulation in plant production.

Comparison of postharvest properties of closely related miniature rose cultivars (Rosa hybrida L.)

Abstract The miniature rose cultivar ‘Vanilla Kordana’ is a useful genetic resource for improving display life and ethylene resistance of miniature potted roses. To investigate the significance of ethylene production and sensitivity as determinants of display life two mutants (‘Goldy, Safari’) selected on external traits and one offspring (‘Champagner’) of ‘Vanilla’ were analysed. All cultivars exhibited a shorter postharvest life and higher ethylene sensitivity than ‘Vanilla’. The cultivar ‘Amber’, which was crossed with ‘Vanilla’ to produce ‘Champagner’, had the shortest display life of the investigated cultivars and was highly ethylene sensitive. In response to exogenous ethylene, ‘Vanilla’ and the related cultivars exhibited differences in display life, chlorophyll loss, leaf and bud drop. The two mutants had a clearly higher ethylene production than ‘Vanilla’, suggesting that this is the main reason for their shorter flower life. ‘Vanilla’ and the mutants did not show autocatalytic stimulation of ethylene production. The ethylene production in ‘Champagner’, which results from crossing of ‘Vanilla’ and ‘Amber’, was lower than in both parents and in the mutants. Ethylene exposure induced increased ethylene production in leaves and partly in flowers of the cultivars ‘Amber’ and ‘Champagner’. This autocatalytic ethylene production may be a major reason for the short display life of these two cultivars. The results indicate that not only initial ethylene production but also degree of autocatalytic stimulation is a major factor determining display life.

Poststorage quality and rooting ability of Epipremnum pinnatum cuttings after treatment with ethylene action inhibitors

SummaryThe influence of the ethylene action inhibitors STS and 1-MCP on poststorage performance and subsequent rooting of cuttings was investigated in Epipremnum pinnatum. Unfavourable storage conditions resulted in decreasing poststorage quality of single-eye cuttings, expressed as leaf drop and yellowing. 1-MCP and STS prohibited leaf drop and yellowing in E. pinnatum. STS pretreatment decreased rooting ability significantly, measured as percentage of rooted cuttings, number of roots, total root length and dry weight. STS caused severe injuries to the cuttings, which were worse if the cuttings were stored rather than propagated immediately. There was no significant difference in rooting between 1-MCP treated cuttings and untreated control in either stored or unstored cuttings. The influence of ethylene action inhibitors on rooting and a possible use of 1-MCP for practical use to increase poststorage performance in cuttings are discussed.

Towards development of new ornamental plants: status and progress in wide hybridization

AbstractMain conclusionThe present review provides insights into the key findings of the hybridization process, crucial factors affecting the adaptation of new technologies within wide hybridization of ornamental plants and presents perspectives of further development of this strategy. Wide hybridization is one of the oldest breeding techniques that contributed enormously to the development of modern plant cultivars. Within ornamental breeding, it represents the main source of genetic variation. During the long history of wide hybridization, a number of methods were implemented allowing the evolution from a conventional breeding tool into a modern methodology. Nowadays, the research on model plants and crop species increases our understanding of reproductive isolation among distant species and partly explains the background of the traditional approaches previously used for overcoming hybridization barriers. Characterization of parental plants and hybrids is performed using molecular and cytological techniques that strongly facilitate breeding processes. Molecular markers and sequencing technologies are used for the assessment of genetic relationships among plants, as the genetic distance is typically depicted as one of the most important factors influencing cross-compatibility in hybridization processes. Furthermore, molecular marker systems are frequently applied for verification of hybrid state of the progeny. The flow cytometry and genomic in situ hybridization are used in the assessment of hybridization partners and characterization of hybrid progeny in relation to genome stabilization as well as genome recombination and introgression. In the future, new research and technologies are likely to provide more detailed information about genes and pathways responsible for interspecific reproductive isolation. Ultimately, this knowledge will enable development of strategies for obtaining compatible lines for hybrid production. Recent development in sequencing technologies and availability of sequence data will also facilitate creation of new molecular markers that will advance marker-assisted selection in hybridization process.

Ethylene resistance in flowering ornamental plants - improvements and future perspectives.

Various strategies of plant breeding have been attempted in order to improve the ethylene resistance of flowering ornamental plants. These approaches span from conventional techniques such as simple cross-pollination to new breeding techniques which modify the plants genetically such as precise genome-editing. The main strategies target the ethylene pathway directly; others focus on changing the ethylene pathway indirectly via pathways that are known to be antagonistic to the ethylene pathway, e.g. increasing cytokinin levels. Many of the known elements of the ethylene pathway have been addressed experimentally with the aim of modulating the overall response of the plant to ethylene. Elements of the ethylene pathway that appear particularly promising in this respect include ethylene receptors as ETR1, and transcription factors such as EIN3. Both direct and indirect approaches seem to be successful, nevertheless, although genetic transformation using recombinant DNA has the ability to save much time in the breeding process, they are not readily used by breeders yet. This is primarily due to legislative issues, economic issues, difficulties of implementing this technology in some ornamental plants, as well as how these techniques are publically perceived, particularly in Europe. Recently, newer and more precise genome-editing techniques have become available and they are already being implemented in some crops. New breeding techniques may help change the current situation and pave the way toward a legal and public acceptance if products of these technologies are indistinguishable from plants obtained by conventional techniques.

Evaluation of reproductive barriers contributes to the development of novel interspecific hybrids in the Kalanchoë genus

BackgroundInterspecific hybridization is a useful tool in ornamental breeding to increase genetic variability and introduce new valuable traits into existing cultivars. The successful formation of interspecific hybrids is frequently limited by the presence of pre- and post-fertilization barriers. In the present study, we investigated the nature of hybridization barriers occurring in crosses between Kalanchoë species and evaluated possibilities of obtaining interspecific hybrids.ResultsThe qualitative and quantitative analyses of pollen tube growth in situ were performed following intra- and interspecific pollinations. They revealed occurrence of pre-fertilization barriers associated with inhibition of pollen germination on the stigma and abnormal growth of pollen tubes. Unilateral incongruity related to differences in pistil length was also observed. The pollen quality was identified as a strong factor influencing the number of pollen tubes germinating in the stigma. In relation to post-fertilization barriers, endosperm degeneration was a probable barrier hampering production of interspecific hybrids. Moreover, our results demonstrate the relation of genetic distance estimated by AFLP marker analysis of hybridization partners with cross-compatibility of Kalanchoë species. At the same time, differences in ploidy did not influence the success of interspecific crosses.ConclusionsOur study presents the first comprehensive analysis of hybridization barriers occurring within Kalanchoë genus. Reproductive barriers were detected on both, pre- and post-fertilization levels. This new knowledge will contribute to further understanding of reproductive isolation of Kalanchoë species and facilitate breeding of new cultivars. For the first time, interspecific hybrids between K. nyikae as maternal plant and K. blossfeldiana as well as K. blossfeldiana and K. marnieriana were generated.