Hybridization is frequent in many organismal groups, but its role in adaptation is poorly understood. In sunflowers, species found in the most extreme habitats are ancient hybrids, and new gene combinations generated by hybridization are speculated to have contributed to ecological divergence. This possibility was tested through phenotypic and genomic comparisons of ancient and synthetic hybrids. Most trait differences in ancient hybrids could be recreated by complementary gene action in synthetic hybrids and were favored by selection. The same combinations of parental chromosomal segments required to generate extreme phenotypes in synthetic hybrids also occurred in ancient hybrids. Thus, hybridization facilitated ecological divergence in sunflowers.

Background: Biochemical models predict that photosynthesis in C₃plants is most frequently limited by the slower of two processes, the maximum capacity of the enzyme Rubisco to carboxylate RuBP (V_c,max), or the regeneration of RuBP via electron transport (J). At current atmospheric [CO₂] levels Rubisco is not saturated; consequently, elevating [CO₂] increases the velocity of carboxylation and inhibits the competing oxygenation reaction which is also catalyzed by Rubisco. In the future, leaf photosynthesis (A) should be increasingly limited by RuBP regeneration, as [CO₂] is predicted to exceed 550 ppm by 2050. The C₃cycle enzyme sedoheptulose-1,7 bisphosphatase (SBPase, EC 3.1.3.17) has been shown to exert strong metabolic control over RuBP regeneration at light saturation.Results: We tested the hypothesis that tobacco transformed to overexpressing SBPase will exhibit greater stimulation ofAthan wild type (WT) tobacco when grown under field conditions at elevated [CO₂] (585 ppm) under fully open air fumigation. Growth under elevated [CO₂] stimulated instantaneousAand the diurnal photosynthetic integral (A') more in transformants than WT. There was evidence of photosynthetic acclimation to elevated [CO₂] via downregulation of V_c,maxin both WT and transformants. Nevertheless, greater carbon assimilation and electron transport rates (J and J_max) for transformants led to greater yield increases than WT at elevated [CO₂] compared to ambient grown plants.Conclusion: These results provide proof of concept that increasing content and activity of a single photosynthesis enzyme can enhance carbon assimilation and yield of C₃crops grown at [CO₂] expected by the middle of the 21st century.

Microarray analysis was performed on RNA isolated from guard cells that were manually dissected from leaves of Arabidopsis. By pooling our data with those of two earlier studies on Arabidopsis guard cell protoplasts, we provide a robust view of the guard-cell transcriptome, which is rich in transcripts for transcription factors, signaling proteins, transporters, and carbohydrate-modifying enzymes. To test the hypothesis that photosynthesis-derived sugar signals guard cells to adjust stomatal opening, we determined the profile of genes expressed in guard cells from leaves that had been treated with sucrose. The results revealed that expression of 440 genes changed in guard cells in response to sucrose. Consistent with this hypothesis, these genes encoded cellular functions for photosynthesis and transport of sugars, water, amino acids, and ions. Plants of T-DNA insertion lines for 50 genes highly responsive to sucrose were examined for defects in guard cell function. Twelve genes not previously known to function in guard cells were shown to be important in leaf conductance, water-use efficiency, and/or stomate development. Of these, three are of particular interest, having shown effects in nearly every test of stomatal function without a change in stomatal density: TPS5 (At4g17770), a TRAF domain-containing protein (At1g65370), and a WD repeat–containing protein (At1g15440).