Enhancement of alkaloid production in opium and California poppy by transactivation using heterologous regulatory factors.

Genes encoding regulatory factors isolated from Arabidopsis, soybean and corn have been screened to identify those that modulate the expression of genes encoding for enzymes involved in the biosynthesis of morphinan alkaloids in opium poppy (Papaver somniferum) and benzophenanthridine alkaloids in California poppy (Eschscholzia californica). In opium poppy, the over-expression of selected regulatory factors increased the levels of PsCOR (codeinone reductase), Ps4'OMT (S-adenosyl-l-methionine:3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase) and Ps6OMT [(R,S)-norcoclaurine 6-O-methyltransferase] transcripts by 10- to more than 100-fold. These transcriptional activations translated into an enhancement of alkaloid production in opium poppy of up to at least 10-fold. In California poppy, the transactivation effect of regulatory factor WRKY1 resulted in an increase of up to 60-fold in the level of EcCYP80B1 [(S)-N-methylcoclaurine 3'-hydroxylase] and EcBBE (berberine bridge enzyme) transcripts. As a result, the accumulations of selected alkaloid intermediates were enhanced up to 30-fold. The transactivation effects of other regulatory factors led to the accumulation of the same intermediates. These regulatory factors also led to the production of new alkaloids in California poppy callus culture.

Expression of human nuclear receptors in plants for the discovery of plant-derived ligands.

Plants have the potential to produce a wide array of secondary metabolites that have utility as drugs to treat human diseases. To tap this potential, functional human nuclear receptors have been expressed in plants to create in planta screening assays as a tool to discover natural product ligands. Assays have been designed and validated using 3 nuclear receptors: the estrogen receptor (ER), the androgen receptor (AR), and the heterodimeric retinoid X receptor-alpha plus thyroid hormone receptor-beta (RXRA/THRB). Nuclear receptor-reporter constructs have been expressed in plants to detect the presence of natural ligands that are produced de novo in several plant species during different stages of development, in various tissues, and in response to different stress elicitors. Screening experiments with ER, AR, and RXRA/THRB have been conducted, leading to the identification of plant sources of natural product ligands of human nuclear receptors. This in planta screen has led to the identification of previously unreported ER ligands, providing evidence of the complementary value of this approach to current in vitro high-throughput screening assays.