The ability to transfer metabolic pathways from the natural producer organisms to the well-characterized cell factory Saccharomyces cerevisiae is well documented. However, as many secondary metabolites are produced by collaborating enzymes assembled in complexes, metabolite production in yeast may be limited by the inability of the heterologous enzymes to collaborate with the native yeast enzymes. This may cause loss of intermediates by diffusion or degradation or due to conversion of the intermediate through competitive pathways. To bypass this problem, we have pursued a strategy in which key enzymes in the pathway are expressed as a physical fusion. As a model system, we have constructed several fusion protein variants in which farnesyl diphosphate synthase (FPPS) of yeast has been coupled to patchoulol synthase (PTS) of plant origin (Pogostemon cablin). Expression of the fusion proteins in S. cerevisiae increased the production of patchoulol, the main sesquiterpene produced by PTS, up to 2-fold. Moreover, we have demonstrated that the fusion strategy can be used in combination with traditional metabolic engineering to further increase the production of patchoulol. This simple test case of synthetic biology demonstrates that engineering the spatial organization of metabolic enzymes around a branch point has great potential for diverting flux toward a desired product.

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To estimate strength parameters of living lodgepole pine stems over a range of temperatures (-16 to +17°C), trees were winched near or past the point of breakage, during which the applied force and deflection of the stem were measured. Trees were 43 years old, 10 m tall, and since the experiments were conducted in the late winter and early spring, when the soil was frozen and the roots were held rigid, the resistance of the stem to deflection could be isolated from the resistances of the root and soil. Static flexure theory for cantilever beams was used to estimate stress, strain, Young's modulus (E), and modulus of rupture (MOR) of the stem. Trees were stiffer and stronger in the winter when wood was frozen, with a nearly 50% increase in E and MOR compared with the spring, when wood was thawed. In winter stems failed on the tension side, while in spring stems buckled on the compression side. Compared with strength estimations reported in the literature from small samples of clear green wood at standard temperatures, modulus of elasticity (MOE) estimates of the whole stem were 35% lower in spring, and in winter MOR exceeded published values by 53%. This suggests that the sway behavior of trees is probably temperature dependent in northern forests and whole-tree strength characteristics should be considered in wind sway models used in these regions.

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Twigs from lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss) trees were bent at a range of temperatures below 0°C using a two-point bending test. This was done to determine how cold temperatures might affect twig breakage and potential shoot and foliage loss in maturing conifer stands. The bending angle necessary to cause 50% twig breakage decreased linearly with decreasing temperatures for both species. No difference in the relationship between temperature and twig breakage was evident among species. Below -13°C, all breakage was on the tension side; at warmer temperatures there was compression damage to many twigs.Résumé : Des rameaux de pin tordu latifolié (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) et d'épinette blanche (Picea glauca (Moench) Voss) ont été pliés à différentes températures au-dessous de 0°C en ayant recours à un test de fléchissement en deux points. Cette expérience visait à déterminer de quelle façon les températures froides affectent le bris des rameaux et la perte potentielle de pousses et d'aiguilles dans les peuplements de conifères à mesure qu'ils vieillissent. L'angle de fléchissement qui entraîne le bris de 50% des rameaux diminue de façon linéaire avec la baisse de température chez les deux espèces. La relation entre la température et le bris des rameaux est semblable chez les deux espèces. Au-dessous de -13°C, tous les bris se sont produits du côté qui était sous tension. Plusieurs rameaux ont subi des dommages dus à la compression à des températures plus chaudes.[Traduit par la Rédaction] Notes 1653