Despite the existence of fluorescent proteins spanning the entire visual spectrum, the bulk of modern imaging experiments continue to rely on variants of the green fluorescent protein derived from Aequorea victoria. Meanwhile, a great deal of recent effort has been devoted to engineering and improving red fluorescent proteins, and relatively little attention has been given to green and yellow variants. Here we report a novel monomeric yellow-green fluorescent protein, mNeonGreen, which is derived from a tetrameric fluorescent protein from the cephalochordate Branchiostoma lanceolatum. This fluorescent protein is the brightest monomeric green or yellow fluorescent protein yet described, performs exceptionally well as a fusion tag for traditional imaging as well as stochastic single-molecule superresolution imaging, and is an excellent FRET acceptor for the newest generation of cyan fluorescent proteins.

In most tree-breeding programs worldwide, increasing the trees' growth rates and stem volumes and shortening their rotation times are important aims. Such trees would yield more biomass per unit area. Here we show that overexpressing a key regulatory gene in the biosynthesis of the plant hormone gibberellin (GA) in hybrid aspen (Populus tremula x P. tremuloides) improves growth rate and biomass. In addition, these transgenic trees have more numerous and longer xylem fibers than unmodified wild-type (wt) plants. Long fibers are desirable in the production of strong paper, but it has not as yet proved possible to influence this trait by traditional breeding techniques. We also show that GA has an antagonistic effect on root initiation, as the transgenic lines showed poorer rooting than the control plants when potted in soil. However, the negative effect on rooting efficiencies in the initial establishment of young plantlets in the growth chamber did not significantly affect root growth at later stages.

Guard cells, which form stomata in leaf epidermes, sense a multitude of environmental signals and integrate this information to regulate stomatal movements. Compared with the advanced understanding of light and water stress responses in guard cells, the molecular mechanisms that underlie stomatal CO(2) signalling have remained relatively obscure. With a high-throughput leaf thermal imaging CO(2) screen, we report the isolation of two allelic Arabidopsis mutants (high leaf temperature 1; ht1-1 and ht1-2) that are altered in their ability to control stomatal movements in response to CO(2). The strong allele, ht1-2, exhibits a markedly impaired CO(2) response but shows functional responses to blue light, fusicoccin and abscisic acid (ABA), indicating a role for HT1 in stomatal CO(2) signalling. HT1 encodes a protein kinase that is expressed mainly in guard cells. Phosphorylation assays demonstrate that the activity of the HT1 protein carrying the ht1-1 or ht1-2 mutation is greatly impaired or abolished, respectively. Furthermore, dominant-negative HT1(K113W) transgenic plants, which lack HT1 kinase activity, show a disrupted CO(2) response. These findings indicate that the HT1 kinase is important for regulation of stomatal movements and its function is more pronounced in response to CO(2) than it is to ABA or light.

. These changes in leaf CO 2 concentrations occur as a result of photosynthesis and respiration. Furthermore, atmospheric CO 2 is predicted to double in the present century (1). Many studies have been carried out to determine the effects of atmospheric CO 2 increases on plant gas exchange, carbon fixation, and growth and the resulting impact this will have on natural and agricultural ecosystems (2-6). One of the mechanisms by which increased atmospheric CO 2 affects plants is CO 2 regulation of stomatal apertures. Reports show that a doubling of atmospheric [CO 2 ] causes significant stomatal closure by 20-40% in diverse plant species (7-9).Stomata experience diurnal changes in [CO 2 ] inside the leaf during light͞dark transitions. In the dark, CO 2 is produced in leaves by cellular respiration. The [CO 2 ] shifts caused by illumination changes are rapid and large, with [CO 2 ] in the stomatal cavity ranging from 200 to 650 ppm (10).Stomatal aperture is controlled by the turgor pressure in the guard cells surrounding the stomatal pore. Guard cell turgor pressure is mediated by the ion and organic solute concentration in guard cells. Elevated CO 2 has been shown to enhance potassium efflux channel and S type anion channel activities that mediate extrusion of ions during stomatal closure (11,12). In correlation with these findings, chloride release from guard cells is triggered by CO 2 elevation (13), and high CO 2 causes depolarization of guard cells (14, 15). Furthermore, CO 2 activation of R type anion channel currents was found in a subset of Vicia faba guard cells (12).Little is known about the CO 2 signal transduction mechanisms that function upstream of ion channels in guard cells (16)(17)(18)(19). CO 2 -induced stomatal movements were previously found to be absent in two mutants that affect the stomatal closure signaling network for the drought stress hormone abscisic acid (ABA): abi1-1 and abi2-1 (20). Conditional CO 2 responsiveness was reported in these mutants by using different experimental conditions (21,22 (16-18, 24, 26-32). Furthermore, some studies have also indicated a role for calcium increases in the opposing response of stomatal opening (33)(34)(35). It is unclear how these opposite responses could be directed via elevations in the same second messenger, Ca 2ϩ .CO 2 is a particularly interesting stomatal stimulus with respect to cytosolic Ca 2ϩ responses, as demonstrated in the present study. CO 2 can induce stomatal opening or closing depending on its concentration (36). Studies in animal and plant cells have shown that different patterns of repetitive calcium transients modulate responses (29,(37)(38)(39). Although previous studies have shown a role for calcium in CO 2 signaling in guard cells (24,25), changes in repetitive calcium transient patterns have not yet been studied in guard cells in response to CO 2 . The present study demonstrates CO 2 modulation of repetitive calcium transient patterns in Arabidopsis guard cells and characterizes roles of Ca 2ϩ in CO 2 -regulated stomatal ope...