Merja Mehto

Activation of Anthocyanin Biosynthesis in Gerbera hybrida (Asteraceae) Suggests Conserved Protein-Protein and Protein-Promoter Interactions between the Anciently Diverged Monocots and Eudicots

We have identified an R2R3-type MYB factor, GMYB10, from Gerbera hybrida (Asteraceae) that shares high sequence homology to and is phylogenetically grouped together with the previously characterized regulators of anthocyanin pigmentation in petunia (Petunia hybrida) and Arabidopsis. GMYB10 is able to induce anthocyanin pigmentation in transgenic tobacco (Nicotiana tabacum), especially in vegetative parts and anthers. In G. hybrida, GMYB10 is involved in activation of anthocyanin biosynthesis in leaves, floral stems, and flowers. In flowers, its expression is restricted to petal epidermal cell layers in correlation with the anthocyanin accumulation pattern. We have shown, using yeast (Saccharomyces cerevisiae) two-hybrid assay, that GMYB10 interacts with the previously isolated bHLH factor GMYC1. Particle bombardment analysis was used to show that GMYB10 is required for activation of a late anthocyanin biosynthetic gene promoter, PGDFR2. cis-Analysis of the target PGDFR2 revealed a sequence element with a key role in activation by GMYB10/GMYC1. This element shares high homology with the anthocyanin regulatory elements characterized in maize (Zea mays) anthocyanin promoters, suggesting that the regulatory mechanisms involved in activation of anthocyanin biosynthesis have been conserved for over 125 million years not only at the level of transcriptional regulators but also at the level of the biosynthetic gene promoters.

GEG Participates in the Regulation of Cell and Organ Shape during Corolla and Carpel Development in Gerbera hybrida

The molecular mechanisms that control organ shape during flower development are largely unknown. By using differential hybridization techniques, a cDNA designated GEG (for Gerbera hybrida homolog of the gibberellin [GA]–stimulated transcript 1 [GAST1] from tomato) was isolated from a library representing late stages of corolla development in Gerbera. GEG expression was detected in corollas and carpels, with expression spatiotemporally coinciding with flower opening. In corollas and styles, GEG expression is temporally correlated with the cessation of longitudinal cell expansion. In plants constitutively expressing GEG, reduced corolla lengths and carpels with shortened and radially expanded stylar parts were found, with concomitant reduction of longitudinal cell expansion in these organs. In addition, in styles, an increase in radial cell expansion was detected. Taken together, these observations indicate a regulatory role for the GEG gene product in determining the shape of the corolla and carpel. The deduced amino acid sequence of the GEG gene product shares high similarity with previously characterized putative cell wall proteins encoded by GA-inducible genes, namely, GAST1, GIP (for GA-induced gene of petunia), and the GASA (for GA-stimulated in Arabidopsis) gene family. Our studies suggest that GEG, the expression of which can also be induced by application of GA3, plays a role in phytohormone-mediated cell expansion.

Androgen Receptor and Mechanism of Androgen Action

Androgen receptor is the intracellular protein that mediates biological actions of physiological androgens (testosterone and 5 alpha-dihydrotestosterone). Androgen receptor belongs to a large family of ligand-dependent proteins whose function is to modulate expression of genes and gene networks in a cell- and tissue-specific manner. The present overview describes the structurally important domains of the receptor protein, and discusses several aspects in the structure-function relationship, using naturally occurring receptor mutants in androgen insensitivity patients or experimental animals as examples. In addition, characteristics of androgen receptor expressed in a heterologous system are described, and their potential usefulness in specific molecular studies discussed.