Exploiting Natural Variation in Tomato to Define Pathway Structure and Metabolic Regulation of Fruit Polyphenolics in the Lycopersicum Complex

While the structures of plant primary metabolic pathways are generally well defined and highly conserved across species,those defining specialized metabolism are less well characterized and more highly variable across species.In this study,we investigated polyphenolic metabolism in the lycopersicum complex by characterizing the underlying biosynthetic and decorative reactions that constitute the metabolic network of polyphenols across eight different species of tomato.For this purpose,GC-MS-and LC-MS-based metabolomics of different tissues of Solatium lycopersicum and wild tomato species were carried out,in concert with the evaluation of cross-hybridized microarray data for MapMan-based transcriptomic analysis,and publicly available RNA-sequencing data for annotation of biosynthetic genes.The combined data were used to compile species-specific metabolic networks of polyphenolic metabolism,allowing the establishment of an entire pan-species biosynthetic framework as well as annotation of the functions of decoration enzymes involved in the formation of metabolic diversity of the flavonoid pathway.The combined results are discussed in the context of the current understanding of tomato flavonol biosynthesis as well as a global view of metabolic shifts during fruit ripening.Our results provide an example as to how large-scale biology approaches can be used for the definition and refinement of large specialized metabolism pathways.

Long-Distance Signaling in bypass1 Mutants： Bioassay Development Reveals the bps Signal to Be a Metabolite

Root-to-shoot signaling is used by plants to coordinate shoot development with the conditions experienced by the roots. A mobile and biologically active compound, the bps signal, is over-produced in roots of an Arabidopsis thaliana mutant called bypass1 （bpsl）, and might also be a normally produced signaling molecule in wild-type plants. Our goal is to identify the bps signal chemically, which will then allow us to assess its production in normal plants. To identify any signaling molecule, a bioassay is required, and here we describe the development of a robust, simple, and quantitative bioassay for the bps signal. The developed bioassay follows the growth-reducing activity of the bps signal using the pCYCB1;I：：GUS cell cycle marker. Wild-type plants carrying this marker, and provided the bps signal through either grafts or metabolite extracts, showed reduced cell division. By contrast, control grafts and treatment with control extracts showed no change in pCYCB1;I：：GUS expression. To determine the chemical nature of the bps signal, extracts were treated with RNase A, Proteinase K, or heat. None of these treatments diminished the activity of bpsl extracts, sug- gesting that the active molecule might be a metabolite. This bioassay will be useful for future biochemical fractionation and analysis directed toward bps signal identification.

Differential Regulation of Carbon Partitioning by the Central Growth Regulator Target of Rapamycin （TOR）

Target of rapamycin （TOR） is an evolutionary conserved ser- ine/threonine protein kinase found in yeast, plants, and ani- mals. TOR plays a central role in sensing nutrients and energy status, growth factors, and other environmental signals, and integrates these cues to synchronize cell growth-related pro- cesses （Laplante and Sabatini, 2012）. In yeast and animal cells, TOR acts as the catalytic component in two structurally and functionally distinct protein complexes termed TORC （TOR complex） 1 and TORC2. TOR seems to be localized specifi- cally to the endomembrane system and the nucleus with a certain mobility, depending on the environmental conditions （Laplante and Sabatini, 2012）. The three major components of TORCl, namely TOR, RAPTOR （Regulatory associated protein of mTOR）, and LST8 （Lethal with Sec13 protein 8）, are present in the genome of Arabidopsis, and interactions between TOR and RAPTOR, as well as TOR and LST8, occur also in plants, indicating the existence of a plant TORC1 （Moreau et al., 2012）. Here, we highlight the possible role of TOR in carbon utilization and growth regulation in Arabidopsis.