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The bioindustrial production of fuels, chemicals, and therapeutics typically relies upon carbohydrate inputs derived from agricultural plants, resulting in the entanglement of food and chemical commodity markets. We demonstrate the efficient production of sucrose from a cyanobacterial species, Synechococcus elongatus, heterologously expressing a symporter of protons and sucrose (cscB). cscB-expressing cyanobacteria export sucrose irreversibly to concentrations of >10 mM without culture toxicity. Moreover, sucrose-exporting cyanobacteria exhibit increased biomass production rates relative to wild-type strains, accompanied by enhanced photosystem II activity, carbon fixation, and chlorophyll content. The genetic modification of sucrose biosynthesis pathways to minimize competing glucose-or sucrose-consuming reactions can further improve sucrose production, allowing the export of sucrose at rates of up to 36.1 mg liter ؊1 h illumination ؊1 . This rate of production exceeds that of previous reports of targeted, photobiological production from microbes. Engineered S. elongatus produces sucrose in sufficient quantities (up to ϳ80% of total biomass) such that it may be a viable alternative to sugar synthesis from terrestrial plants, including sugarcane.

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The homeo-box-containing gene niec-3 of the nematode Caenorhabditis elegans, is expressed in several sensory neurons, as assayed by expression of a mec-3-lacZ fusion. These cells are the touch receptors, which mediate the response to gentle touch, and the FLF and PVD neurons. PVD mediates a response to harsh mechanical stimuli, and FLP has an ultrastructure suggestive of a mechanoreceptor, but its function is unknown, mec-3 is necessary for the differentiation of the touch receptors, because in niec-3 mutants, the touch receptors do not function and have none of their distinguishing features, mec-3 is also needed for PVD function: The PVD neurons no longer mediate a response to harsh mechanical stimuli in the mutants. The expression of the mec-3-lacZ fusion, and presumably mec-3 itself, is altered by mutations in several genes originally identified by their effects on touch cell development, unc-86, another homeo-box-containing gene, is necessary for all mec-3-lacZ expression, but also affects several other lineages and cells in which mec-3 is not expressed, mec-3 activity appears to be required for maintained expression of the mec-3-lacZ fusion in all cells in which it is expressed. In a mec-17 mutant, mec-3-lacZ expression is not maintained in the touch receptors, but is not affected in the FLP and PVD neurons. These findings suggest that combinatorial mechanisms of gene regulation control both the expression of mec-3 itself and its action in promoting the terminal differentiation of various cell types.