Kinetic mathematical models facilitated the discovery of feedback control, GT developmental patterns, and epigenetic processes as critical determinants of metabolic outcomes ( Rios-Estepa et al., 2008, 2010 Lange and Rios-Estepa, 2014 Ahkami et al., 2015). These data sets also enabled the cloning and characterization of genes encoding the entire complement of enzymes responsible for p-menthane monoterpenoid biosynthesis in peppermint ( Lange et al., 1998 Burke et al., 1999 Lange and Croteau, 1999a, 1999b Ringer et al., 2003, 2005 Davis et al., 2005). In the mid to late 1990s, these protocols were modified to allow the development of an EST library, the sequencing of which revealed the stunning metabolic specialization of mint GTs ( Lange et al., 2000). Pioneering studies in the late 1980s and early 1990s reported on methods for purifying secretory cells of GTs away from other leaf cell types and established that the entire biosynthetic pathway from imported sugars to the monoterpene end products is confined to these specialized cell types ( Gershenzon et al., 1992 McCaskill et al., 1992 McCaskill and Croteau, 1995). Peppermint ( Mentha × piperita) and its close relatives have a long history as model systems for furthering our understanding of GT structure and function. GTs are particularly widespread across the angiosperm lineages and accumulate, among others, the specialized metabolites responsible for the psychoactive effects of cannabis ( Cannabis sativa), the bitter flavor of hops ( Humulus lupulus), the insect-repellant principles of tomato ( Solanum lycopersicum) leaves, the antimalarial activity of sweet wormwood ( Artemisia annua), and the essential oils of members of the Lamiaceae ( Lange and Turner, 2013). Some examples are resin ducts, secretory cavities, glandular trichomes ( GTs), laticifers, and gum ducts ( Fahn, 1988). Anatomical structures that harbor specialized metabolic pathways can take many forms and vary widely across the plant lineages. Plant secondary (or specialized) metabolites are frequently synthesized and accumulated in specialized tissues or cell types. This study provides, to our knowledge, the first evidence of how bioenergetic processes determine flux through monoterpene biosynthesis in GTs. We also report that GTs with high flux toward monoterpenes express, at very high levels, genes coding for a unique pair of ferredoxin and ferredoxin-NADP + reductase isoforms.
Follow-up biochemical assays with isolated GTs indicated that oxidative phosphorylation and ethanolic fermentation were active and that cooperation to provide ATP depended on the concentration of the carbon source. Using simulated reaction deletions, this model predicted that two processes, the regeneration of ATP and ferredoxin (in its reduced form), exert substantial control over flux toward monoterpenes. Fluxes through the network were predicted based on metabolomic and transcriptomic data.
A genome-scale stoichiometric model of secretory phase metabolism in peppermint GTs was constructed based on current biochemical and physiological knowledge. The commercially important essential oils of peppermint ( Mentha × piperita) and its relatives in the mint family (Lamiaceae) are accumulated in specialized anatomical structures called glandular trichomes ( GTs).
0 kommentar(er)
