Plant cell cultures as heterologous bio-factories for secondary metabolite production

Synthetic biology has been developing rapidly in the last decade and is attracting increasing attention from many plant biologists.The production of high-value plant-specific secondary metabolites is,however,limited mostly to microbes.This is potentially problematic because of incorrect post-translational modification of proteins and differences in protein micro-compartmentalization,substrate availability,chaperone availability,product toxicity,and cytochrome p450 reductase enzymes.Unlike other heterologous systems,plant cells may be a promising alternative for the production of high-value metabolites.Several commercial plant suspension cell cultures from different plant species have been used successfully to produce valuable metabolites in a safe,low cost,and environmentally friendly manner.However,few metabolites are currently being biosynthesized using plant platforms,with the exception of the natural pigment anthocyanin.Both Arabidopsis thaliana and Nicotiana tabacum cell cultures can be developed by multiple gene transformations and CRISPR-Cas9 genome editing.Given that the introduction of heterologous biosynthetic pathways into Arabidopsis and N.tabacum is not widely used,the biosynthesis of foreign metabolites is currently limited;however,therein lies great potential.Here,we discuss the exemplary use of plant cell cultures and prospects for using A.thaliana and N.tabacum cell cultures to produce valuable plant-specific metabolites.

Two mitochondrial phosphatases,PP2c63 and Sal2,are required for posttranslational regulation of the TCA cycle in Arabidopsis

Protein phosphorylation is a well-established post-translational mechanism that regulates protein functions and metabolic pathways.It is known that several plant mitochondrial proteins are phosphorylated in a reversible manner.However,the identities of the protein kinases/phosphatases involved in this mech-anism and their roles in the regulation of the tricarboxylic acid(TCA)cycle remain unclear.In this study,we isolated and characterized plants lacking two mitochondrially targeted phosphatases(Sal2 and PP2c63)along with pyruvate dehydrogenase kinase(PDK),Protein-protein interaction analysis,quantitative phos-phoproteomics,and enzymatic analyses revealed that PDK specifically regulates pyruvate dehydrogenase complex(PDC),while PP2c63 nonspecifically regulates PDC.When recombinant PP2c63 and Sal2 proteins were added to mitochondria isolated from mutant plants,protein-protein interaction and enzymatic analyses showed that PP2c63 directly phosphorylates and modulates the activity of PDC,while Sal2 only indirectly affects TCA cycle enzymes.Characterization of steady-state metabolite levels and fluxes in the mutant lines further revealed that these phosphatases regulate flux through the TCA cycle,and that altered metabolism in the sa/2 pp2c63 double mutant compromises plant growth.These results are discussed in the context of current models of the control of respiration in plants.