Self-regulation of phytoalexin production: a non-biosynthetic enzyme controls alkaloid biosynthesis in cultured cells of Eschscholzia californica

• Published in: Plant cell, tissue and organ culture Vol. 119; no. 3; pp. 661 - 676
• Main Authors: Müller, Henriette, Heinze, Michael, Heinke, Ramona, Schmidt, Jürgen, Roos, Werner
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer-Verlag 01.12.2014; Springer Netherlands; Springer Nature B.V
• Subjects: Alkaloids; Antimicrobial agents; Automatic control; Biomedical and Life Sciences; Biosynthesis; Cell walls; cultured cells; Cytoplasm; Cytotoxicity; Drug development; Enzymes; Eschscholzia californica; Lead compounds; Life Sciences; mutants; Original Paper; Papaveraceae; phenotype; Phenotypes; Phospholipase; Phospholipase A2; phytoalexins; Plant Genetics and Genomics; Plant Pathology; Plant Physiology; Plant Sciences; plasma membrane; Reductase; Reductases; RNA-mediated interference; Sanguinarine; Substrate inhibition; Toxicity; Phytoalexins; Plant signal transfer; Benzophenanthridine alkaloids; Plant secondary metabolism; Environmental stress
• ISSN: 0167-6857; 1573-5044
• DOI: 10.1007/s11240-014-0565-6

Benzophenanthridine alkaloids are strong antimicrobials of Papaveraceae and attractive lead compounds for drug development. The cytotoxicity of these compounds requires the producing plant to limit the pathogen-triggered burst of biosynthesis. Cells of Eschscholzia californica excrete early benzophenanthridines to the cell wall, followed by re-uptake and reduction in the cytoplasm by the detoxifying enzyme sanguinarine reductase. We now discovered that this enzyme is a core component of self-control in alkaloid production. RNAi-based silencing of sanguinarine reductase gave rise to mutants that either show a complete stop of elicitor-triggered alkaloid production or a burst of biosynthesis that severalfold surpasses the wild type level. These unexpected phenotypes reflect impacts of substrate or product of sanguinarine reductase: the substrate, sanguinarine, inhibits phospholipase A2 at the plasma membrane, an initial component of the signal path towards expression of biosynthetic enzymes. The product, dihydrosanguinarine, inhibits enzymes of early biosynthesis, prior to reticuline formation. By tuning these steady states, sanguinarine reductase adjusts the capacity of alkaloid biosynthesis: a minimum activity is sufficient to prevent the blockade of the induction pathway by sanguinarine, while the full activity of the same enzyme causes a limitation of the biosynthetic flow via dihydrosanguinarine.