ABSTRACT
Although phosphorus is an essential factor for proper plant growth in natural environments, an excess of phosphate in water sources causes serious pollution. In this paper we describe transgenic plants which hyperaccumulate inorganic phosphate (Pi) and which may be used to reduce environmental water pollution by phytoremediation. AtPHR1, a transcription factor for a key regulator of the Pi starvation response in Arabidopsis thaliana, was overexpressed in the ornamental garden plants Torenia, Petunia, and Verbena. The transgenic plants showed hyperaccumulation of Pi in leaves and accelerated Pi absorption rates from hydroponic solutions. Large-scale hydroponic experiments indicated that the enhanced ability to absorb Pi in transgenic torenia (AtPHR1) was comparable to water hyacinth a plant that though is used for phytoremediation causes overgrowth problems.
Subject(s)
Genetic Engineering , Lamiaceae/metabolism , Petunia/metabolism , Phosphates/metabolism , Verbena/metabolism , Absorption , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Biodegradation, Environmental , Hydroponics , Lamiaceae/genetics , Petunia/genetics , Phosphorus/metabolism , Plants, Genetically Modified , Transcription Factors/genetics , Transcription Factors/metabolism , Verbena/geneticsABSTRACT
Flower color is mainly determined by the structure of flavonoids, a group of secondary metabolites of plants. The biosynthetic pathway and the genes involved in the pathway are well characterized such that it is possible to change flower color by engineering the pathway by overexpression of heterologous genes and/or suppression of endogenous genes in transgenic plants. Trimming an unnecessary pathway by suppression of endogenous genes is often essential to achieve successful engineering of the pathway and the resultant accumulation of desirable compounds. RNAi by transcription of double-stranded RNA (dsRNA) is a powerful and efficient method to command such suppression and is widely used for artificial gene suppression in transgenic plants.
Subject(s)
Biosynthetic Pathways/genetics , Flavonoids/biosynthesis , Flowers , Plants, Genetically Modified , RNA Interference , Color , Flowers/anatomy & histology , Flowers/physiology , Gene Expression Regulation, Plant , Genetic Vectors/genetics , Genetic Vectors/metabolism , Oxygenases/genetics , Oxygenases/metabolism , Plant Proteins/genetics , Plant Proteins/metabolism , RNA, Double-Stranded/genetics , RNA, Double-Stranded/metabolism , Transformation, GeneticABSTRACT
Flower color is mainly determined by anthocyanins. Rosa hybrida lacks violet to blue flower varieties due to the absence of delphinidin-based anthocyanins, usually the major constituents of violet and blue flowers, because roses do not possess flavonoid 3',5'-hydoxylase (F3'5'H), a key enzyme for delphinidin biosynthesis. Other factors such as the presence of co-pigments and the vacuolar pH also affect flower color. We analyzed the flavonoid composition of hundreds of rose cultivars and measured the pH of their petal juice in order to select hosts of genetic transformation that would be suitable for the exclusive accumulation of delphinidin and the resulting color change toward blue. Expression of the viola F3'5'H gene in some of the selected cultivars resulted in the accumulation of a high percentage of delphinidin (up to 95%) and a novel bluish flower color. For more exclusive and dominant accumulation of delphinidin irrespective of the hosts, we down-regulated the endogenous dihydroflavonol 4-reductase (DFR) gene and overexpressed the Irisxhollandica DFR gene in addition to the viola F3'5'H gene in a rose cultivar. The resultant roses exclusively accumulated delphinidin in the petals, and the flowers had blue hues not achieved by hybridization breeding. Moreover, the ability for exclusive accumulation of delphinidin was inherited by the next generations.
