Live Imaging of Shoot Meristems on an Inverted Confocal Microscope Using an Objective Lens Inverter Attachment

Live imaging of above ground meristems can lead to new insights in plant development not possible from static imaging of fixed tissue. The use of an upright confocal microscope offers several technical and biological advantages for live imaging floral or shoot meristems. However, many departments and core facilities possess only inverted confocal microscopes and lack the funding for an additional upright confocal microscope. Here we show that imaging of living apical meristems can be performed on existing inverted confocal microscopes with the use of an affordable and detachable InverterScope accessory.

Fluorescent and bimolecular-fluorescent protein tagging of genes at their native loci in Neurospora crassa using specialized double-joint PCR plasmids

The double-joint polymerase chain reaction (DJ-PCR) is a technique that can be used to construct vectors for targeted genome integration without laborious subcloning steps. Here we report the availability of plasmids that facilitate DJ-PCR-based construction of Neurospora crassa tagging vectors. These plasmids allow the creation of green or red fluorescent protein (GFP or RFP) tagging vectors for protein localization studies, as well as split-yellow fluorescent protein (YFP) tagging vectors for bimolecular fluorescence complementation (BiFC) analyses. We have demonstrated the utility of each plasmid with the tagging of known meiotic silencing proteins. Microscopic analysis of the tagged strains indicates that SMS-2 and QIP form macromolecular complexes in the perinuclear region during meiosis.

The Arabidopsis histidine phosphotransfer proteins are redundant positive regulators of cytokinin signaling

Arabidopsis thaliana histidine phosphotransfer proteins (AHPs) are similar to bacterial and yeast histidine phosphotransfer proteins (HPts), which act in multistep phosphorelay signaling pathways. A phosphorelay pathway is the current model for cytokinin signaling. To assess the role of AHPs in cytokinin signaling, we isolated T-DNA insertions in the five AHP genes that are predicted to encode functional HPts and constructed multiple insertion mutants, including an ahp1,2,3,4,5 quintuple mutant. Single ahp mutants were indistinguishable from wild-type seedlings in cytokinin response assays. However, various higher-order mutants displayed reduced sensitivity to cytokinin in diverse cytokinin assays, indicating both a positive role for AHPs in cytokinin signaling and functional overlap among the AHPs. In contrast with the other four AHPs, AHP4 may play a negative role in some cytokinin responses. The quintuple ahp mutant showed various abnormalities in growth and development, including reduced fertility, increased seed size, reduced vascular development, and a shortened primary root. These data indicate that most of the AHPs are redundant, positive regulators of cytokinin signaling and affect multiple aspects of plant development.

A Golgi-localized hexose transporter is involved in heterotrimeric G protein-mediated early development in Arabidopsis

Signal transduction involving heterotrimeric G proteins is universal among fungi, animals, and plants. In plants and fungi, the best understood function for the G protein complex is its modulation of cell proliferation and one of several important signals that are known to modulate the rate at which these cells proliferate is D-glucose. Arabidopsis thaliana seedlings lacking the beta subunit (AGB1) of the G protein complex have altered cell division in the hypocotyl and are D-glucose hypersensitive. With the aim to discover new elements in G protein signaling, we screened for gain-of-function suppressors of altered cell proliferation during early development in the agb1-2 mutant background. One agb1-2-dependent suppressor, designated sgb1-1(D) for suppressor of G protein beta1 (agb1-2), restored to wild type the altered cell division in the hypocotyl and sugar hypersensitivity of the agb1-2 mutant. Consistent with AGB1 localization, SGB1 is found at the highest steady-state level in tissues with active cell division, and this level increases in hypocotyls when grown on D-glucose and sucrose. SGB1 is shown here to be a Golgi-localized hexose transporter and acts genetically with AGB1 in early seedling development.

Mitochondrial involvement in tracheary element programmed cell death

The mitochondria pathway is regarded as a central component of some types of programmed cell death (PCD) in animal cells where specific signals cause the release of cytochrome c from mitochondria to trigger a proteolytic cascade involving caspases. However, plant cells lack canonical caspases, therefore a role for the mitochondria in programmed cell death in plant cells is not obvious. Using plant cells which terminally differentiate, we provide evidence supporting the involvement of mitochondria in PCD, however the release of cytochrome c is insufficient to trigger the PCD. Prior to execution of cellular autolysis initiated by the rupture of the large central vacuole to release sequestered hydrolases, mitochondria adopt a definable morphology, the inner membrane depolarizes prior to death, and cytochrome c is released from mitochondria. However, PCD can be blocked despite translocation of cytochrome c. These results suggest a role for the mitochondria in this PCD but do not support the current animal model for a causative role of cytochrome c in triggering PCD.

Distribution of transforming growth factor-beta 1, fibronectin, and smooth muscle actin in asbestos-induced pulmonary fibrosis in rats

We are studying the development of fibrogenic lesions in the lungs of rats exposed briefly to an aerosol of chrysotile asbestos fibers. This model of asbestosis has enabled us to establish very early cellular events at the specific locations where interstitial fibrosis will develop. These sites, the first alveolar duct bifurcations, are where the fibers are initially deposited and where macrophages first accumulate. In the studies presented here, we used immunohistochemical techniques to show that these macrophages exhibit strong localization of transforming growth factor-beta. In the adjacent developing fibrogenic lesions a clear increase in fibronectin staining was demonstrated and morphological analysis indicated a significant increase in amounts of smooth muscle actin. Such studies are essential in furthering our understanding of the distribution of potential mediators of the fibrogenic process and the cellular responses they elicit during the pathogenesis of disease.