Reprogramming of primary metabolism facilitates metabolic engineering of bioactives in tomato fruit

Phenylpropanoids are derived from phenylalanine and comprise an important class of plant secondary metabolites that include specialized bioactives with medicinal properties, important phytonutrients, a broad range of natural colours, phytoanticipins, phytoalexins and phytoestrogens. A number of transcription factors have been used to upregulate specific branches of phenylpropanoid metabolism, but by far the most effective has been the fruit-specific expression of AtMYB12 in tomato, which resulted in an astonishing 10% of fruit dry weight accumulating as flavonoids and hydroxycinnamates. We show that AtMYB12 not only increases the demand of flavonoid biosynthesis, but also increases the supply of carbon from primary metabolism, and the supply of energy and reducing power, by upregulating glycolysis, the TCA cycle, the oxidative pentose phosphate pathway, fuelling the shikimate and phenylalanine biosynthetic pathways to supply more aromatic amino acids for secondary metabolism. AtMYB12 directly activates at least some genes encoding enzymes of primary metabolism. The enhanced supply of precursors, energy and reducing power achieved by AtMYB12 expression can be harnessed to engineer high levels of novel phenylpropanoids in tomato fruit, offering an effective production system for bioactives and other high value ingredients. Overall design: WT (MicroTom), AtMYB12, Del/Ros and Indigo trasgenic fruits were harvested after 1 week and 4 weeks after breaker stage. Pericarp from harvested fruits was used for total RNA extraction. mRNA profiles were generated by deep sequencing on Illumina GAIIx using EXPRSS tag-seq protocol.