Generation of Phenylpropanoid Pathway-Derived Volatiles in Transgenic Plants: Rose Alcohol Acetyltransferase Produces Phenylethyl Acetate and Benzyl Acetate in Petunia Flowers

Esters are important contributors to the aroma of numerous flowers and fruits. Acetate esters such as geranyl acetate, phenylethyl acetate and benzyl acetate are generated as a result of the action of alcohol acetyltransferases (AATs). Numerous homologous AATs from various plants have been characterized using in-vitro assays. To study the function of rose alcohol acetyltransferase (RhAAT) in planta , we generated transgenic petunia plants expressing the rose gene under the control of a CaMV-35S promoter. Although the preferred substrate of RhAAT in vitro is geraniol, in transgenic petunia flowers, it used phenylethyl alcohol and benzyl alcohol to produce the corresponding acetate esters, not generated by control flowers. The level of benzyl alcohol emitted by the flowers of different transgenic lines was ca. three times higher than that of phenylethyl alcohol, which corresponded to the ratio between the respective products, i.e. ca. three times more benzyl acetate than phenylethyl acetate. Feeding of transgenic petunia tissues with geraniol or octanol led to the production of their respective acetates, suggesting the dependence of volatile production on substrate availability.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43457/1/11103_2005_Article_4924.pd

Molecular Control of Floral Organogenesis in Higher Plants: the Abcd Model

Plants are an important group of organisms which are capable of auxotrophic growth and therefore have a vital function to maintain life on earth. Although a number of plant species reproduce asexually, most plant species use specialised structures, flowers, for sexual reproduction. Compared with animal systems surprisingly little is known about the molecular processes governing organogenesis. However during the last five years a number of regulatory genes have been identified, isolated and characterized which are controlling the onset of developmental programmes leading to the determination and development of the various floral organs. The function of these genes was studied using genetic and molecular genetic techniques. Three classes of genes can be discriminated which are determining the developmental switches from vegetative meristem (class I), via floral meristem (class II) into the various organ primordia (class III). The genes involved encode transcription factors which function in a complex network of regulatory proteins. The final fates of the floral organ primordia are determined by the so-called ABCD genes. The activity of those genes can be summarised in the ABCD model which provides a simplified way to describe how the identity of each floral organ is determined

Flavonols are not essential for fertilization in Arabidopsis thaliana

Flavonols are plant metabolites suggested to serve a vital role in fertilization of higher plants. Petunia and maize plants mutated in their flavonol biosynthesis are not able to set seed after self-pollination. We have investigated the role of these compounds in Arabidopsis thaliana. Like in all other plant species, high levels of flavonols could be detected in pollen of wild-type A. thaliana. No flavonols were detected in reproductive organs of the A. thaliana tt4 mutant in which the ohs gene is mutated. Surprisingly, this mutant did set seed after self-fertilization and no pollen tube growth aberrations were observed in vivo. The role of flavonols during fertilization of Arabidopsis is discussed

Promoter activity of a putative pollen monosaccharide transporter in Petunia hybrida and characterisation of a transposon insertion mutant

For the growth of the male reproductive cells of plants, the pollen, the presence of sufficient sucrose or monosaccharides is of vital importance. From Petunia hybrida a pollen-specific putative monosaccharide transporter designated PMT1 (for petunia monosaccharide transporter) has been identified previously. The present work provides an in-depth analysis and characterisation of PMT1 in the context of pollen development with the GUS reporter gene and an insertion mutant. The promoter of the pollen-specific putative PMT1 gene has been isolated by inverse PCR and sequenced. Analysis of plants transformed with the promoter-GUS fusion confirmed the specificity of this gene, belonging to the late pollen-specific expressed genes. GUS activity was detected even after 24 h of in vitro pollen germination, at the pollen tube tip. To elucidate the importance of PMT1 for gametophyte development and fertilisation, we isolated a mutant plant containing a transposon insertion in the PMT1 gene by the dTph1 transposon-tagging PCR-based assay. The PMT1 mutant contained a dTph1 insertion in position 1474 bp of the transcribing part of the gene, before the last two transmembrane-spanning domains. Analysis of the progeny of the heterozygous mutant after selfing revealed no alterations in pollen viability and fertility. Mature pollen grains of a plant homozygous for the transposon insertion were able to germinate in vitro in a medium containing sucrose, glucose, or fructose, which indicates that PMT1 is not essential for pollen survival. Several explanations for these results are discussed in the present work

Flavonols are not essential for fertilization in Arabidopsis thaliana

Flavonols are plant metabolites suggested to serve a vital role in fertilization of higher plants. Petunia and maize plants mutated in their flavonol biosynthesis are not able to set seed after self-pollination. We have investigated the role of these compounds in Arabidopsis thaliana. Like in all other plant species, high levels of flavonols could be detected in pollen of wild-type A. thaliana. No flavonols were detected in reproductive organs of the A. thaliana tt4 mutant in which the ohs gene is mutated. Surprisingly, this mutant did set seed after self-fertilization and no pollen tube growth aberrations were observed in vivo. The role of flavonols during fertilization of Arabidopsis is discussed