The development of a sustainable agriculture and the use of plants for biomass energy and green chemistry require biochemical plant engineering to re-channel plant metabolism. These objectives are presently impeded by our poor understanding of critical metabolic steps that control complex plant metabolic networks and by the lack of an integrative and dynamic view of plant metabolism. Indeed, several studies have shown that the manipulation of single metabolic steps cannot lead to significant improvements in plant biomass production and rather, the complex corpus of interacting metabolic pathways has to be considered as a whole. Although intense efforts have been devoted to integrative metabolic fingerprints and metabolomics over the past 10 years, the measurement of metabolic fluxes through multiple pathways (fluxomics) of primary metabolisms (e.g. C, N, S assimilation or lipid production) is a prerequisite to identify the (multiple) enzymatic targets or metabolic bottlenecks that require improvement. This approach should allow to predict how to increase plant yield while reducing inputs, improve plant biomass for bio-fuels and seed quality, etc. The molecules of plant origin, especially cellulose and lipids, are substitutes in applications in energy or green chemistry. More than 300 different fatty acids are found in plants. Their physical properties and chemical reactivity are of great interest for syntheses of new compounds. Fatty acids are found in consumer (food, soap, cleaning products) or industrial products (solvents, oils, varnish, ink). For instance, dicarboxylic acids produced by chemical or biological oxidation of oleic acid can be used for the manufacture of nylon. Roadblocks to use plant lipids range from the extensive identification of relevant molecules in various species to the study of the mechanisms governing their accumulation (identification of regulatory genes, deciphering of interaction networks) and methods for their extraction and processing. There is also a need to develop sustainable sources of nutritionally important fatty acids such as those that are typically derived from fish oil. There is an ever-increasing awareness of the value of nutrition and a strong demand for proteins with good nutritive value (equilibrated amino acid composition, content in essential amino acids devoid of allergenicity). Understanding the mechanisms governing accumulation of reserve proteins, and improvement of their quality are also important issues. Last, the novel grass model Brachypodium is being adopted for cell wall research for biomass production. Given its evolutionary proximity, this species will allow easy transfer to wheat research. The 4x genome sequence is available and an 8x sequence will be released soon. INRA is financing the development of novel genomics tools in this species (efficient transformation procedure, insertion collections and tilling population, contribution to transcriptome compendium).

Important scientific issues in this field are for instance

• Structure and regulation of metabolic pathways (biosynthesis, transport, and storage)
• Biosynthesis of biomass adapted to energy production (e.g. ligno-cellulose, oil, sugars)
• Specific molecules for green chemistry (e.g. ligno-cellulose, oil, lipids, proteins, sugars)
• Production of secondary metabolites and high quality proteins for nutrition and health