Towards engineering increased pantothenate (Vitamin B5) levels in plants

Abstract

Pantothenate (vitamin B5) is the precursor of the 4'-phosphopantetheine moiety of coenzyme A and acyl-carrier protein. It is made by plants and microorganisms de novo, but is a dietary requirement for animals. The pantothenate biosynthetic pathway is well-established in bacteria, comprising four enzymic reactions catalysed by ketopantoate hydroxymethyltransferase (KPHMT), L-aspartate-a-decarboxylase (ADC), pantothenate synthetase (PS) and ketopantoate reductase (KPR) encoded by panB, panD, panC and panE genes, respectively. In higher plants the genes encoding the first (KPHMT) and last (PS) enzymes have been identified and characterized in several plant species. Commercially, pantothenate is chemically synthesised and used in vitamin supplements, feed additives and cosmetics. Biotransformation is an attractive alternative production system that would circumvent the expensive procedures of separating racemic intermediates. The authors have explored the possibility of manipulating pantothenate biosynthesis in plants. Transgenic Oilseed rape (Brassica napus) lines were generated in which the E. coli KPHMT and PS genes were expressed under a strong constitutive CaMV 35SS promoter. No significant changes of pantothenate levels in PS transgenic lines was observed. In contrast plants expressing KPHMT had elevated pantothenate level in leaves, flowers siliques and seed in the range of 1.5 to 2.5 fold increase compared to the wild type plant. Seeds contained the highest vitamin content indicating that they might be the ideal target for production purposes. The results also suggest that KPHMT might be the rate limiting step in pantothenate biosynthesis, and that cells and/or tissues make pantothenate just enough for immediate metabolic needs