Isoprenoids are a very large and diverse family of metabolites required by all living organisms. All isoprenoids derive from the double-bond isomers isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are produced by the methylerythritol 4-phosphate (MEP) pathway in bacteria and plant plastids. Understanding the regulation of the MEP pathway, probably the main metabolic pathway elucidated in this century, is a must for the rational design of biotechnological endeavors aimed at increasing isoprenoid contents in microbial and plant systems. It has been reported that IPP and DMAPP feedback regulate the activity of deoxyxylulose 5-phosphate (DXS), a dimeric enzyme catalyzing the main flux-controlling step of the MEP pathway. Here we provide experimental insights on the underlying mechanism. Our data show that direct allosteric binding of IPP and DMAPP to bacterial and plant DXS promotes monomerization of the enzyme. This allows a fast response to a sudden increase or decrease in IPP/DMAPP supply by rapidly shifting the dimer-monomer equilibrium accordingly. DXS monomers expose hydrophobic domains that are hidden in the dimer, resulting in aggregation and eventual degradation. Removal of monomers that would otherwise be available for dimerization and enzyme reactivation appears as a more drastic response in case of persistent IPP/DMAPP overabundance (e.g., by a blockage in their conversion to downstream isoprenoids). Our model provides a mechanistic explanation of how IPP and DMAPP supply can be adapted to changes in their demand and it also explains the changes in DXS protein levels observed after long-term interference of the MEP pathway flux.Significance StatementIsoprenoids are a vast family of organic compounds with essential roles in respiration, photosynthesis, photoprotection, membrane structure, and signaling. Many of them have great economic and nutritional relevance as pigments, aromas, drugs or phytonutrients. Despite their functional and structural diversity, they all derive from the same five-carbon precursors. We show that these precursors feedback-regulate their own synthesis in bacteria and plant plastids by allosterically shifting the dimer:monomer equilibrium of the enzyme that catalyzes the first step of their biosynthetic pathway towards the inactive monomeric form. This evolutionary conserved mechanism allows for both short-term (immediate) and long-term (sustained) control of the pathway flux, and its manipulation could be critical for the rational engineering of high-value isoprenoid products in bacterial and plant systems.
Brassinosteroids (BR) plays an important role in regulating plant growth. We found that the expression of BR synthesis and signal transduction genes were up-regulation when potato dormancy was released, and suckering agents can inhibit the expression of Methylsterol monooxygenase 1 (SMO1), Delta24-sterol reductase 1 (DWF1), Protein BR insensitive 1 (BRI1), BR-signaling kinase (BSK) and Cyclin D3 (CYCD3) genes in potato tuber. Besides, we found that the storage period among different cultivars are significant different at low temperature. Low temperature can obviously extend cultivar 'Favorita' storage time than cultivar 'Mira'. In order to explore the response of BR genes to potato sprout at low temperature. This study will analyze the expression of BR synthesis, signal transduction and regulation genes at from cultivar 'Favorita' and cultivar 'Mira' which both cultivars are storage at low temperature (4°C) and room temperature (23±2)°C environment by qRT-PCR technique. The results showed that the expression of DWF1 and BRI1 are decreased in both cultivars by low temperature treatment. The expression of SMO1, BSK and CYCD3 genes are decreased in cultivar 'Favorita'by low temperature treatment. While, the expression of SMO1, BSK and CYCD3 genes in'Mira'are increase by temperature treatment. It shows that low temperature influences the expression of SMO1, BSK and CYCD3 genes in cultivar 'Favorita', which results in the long dormancy period of the cultivar 'Favorita'. These results will provide the theoretical basis in elucidating the BR mechanism of potato sprout, breeding variety selection and new technology research and development of potato storage regulation.
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