Showing papers by "Klaus Palme published in 2012"
TL;DR: The data show a functional role for endoplasmic reticulum-localized PIN8 and suggest a mechanism whereby PIN8 controls auxin thresholds and access of auxin to the nucleus, thereby regulating auxin-dependent transcriptional activity.
Abstract: SUMMARY The plant hormone auxin is a mobile signal which affects nuclear transcription by regulating the stability of auxin/indole-3-acetic acid (IAA) repressor proteins. Auxin is transported polarly from cell to cell by auxin efflux proteins of the PIN family, but it is not as yet clear how auxin levels are regulated within cells and how access of auxin to the nucleus may be controlled. The Arabidopsis genome contains eight PINs, encoding proteins with a similar membrane topology. While five of the PINs are typically targeted polarly to the plasma membranes, the smallest members of the family, PIN5 and PIN8, seem to be located not at the plasma membrane but in endomembranes. Here we demonstrate by electron microscopy analysis that PIN8, which is specifically expressed in pollen, resides in the endoplasmic reticulum and that it remains internally localized during pollen tube growth. Transgenic Arabidopsis and tobacco plants were generated overexpressing or ectopically expressing functional PIN8, and its role in control of auxin homeostasis was studied. PIN8 ectopic expression resulted in strong auxin-related phenotypes. The severity of phenotypes depended on PIN8 protein levels, suggesting a rate-limiting activity for PIN8. The observed phenotypes correlated with elevated levels of free IAA and ester-conjugated IAA. Activation of the auxin-regulated synthetic DR5 promoter and of auxin response genes was strongly repressed in seedlings overexpressing PIN8 when exposed to 1-naphthalene acetic acid. Thus, our data show a functional role for endoplasmic reticulum-localized PIN8 and suggest a mechanism whereby PIN8 controls auxin thresholds and access of auxin to the nucleus, thereby regulating auxindependent transcriptional activity.
151 citations
TL;DR: It is suggested that a prolonged nitrate depletion may induce post-transcriptionally the expression of target genes by repressing the transcription of specific miRNAs upon nitrate shortage.
Abstract: Nitrogen availability seriously affects crop productivity and environment. The knowledge of post-transcriptional regulation of plant response to nutrients is important to improve nitrogen use efficiency of crop. This research was aimed at understanding the role of miRNAs in the molecular control of plant response to nitrate. The expression profiles of six mature miRNAs were deeply studied by quantitative real time polymerase chain reaction and in situ hybridization (ISH). To this aim, a novel optimized protocol was set up for the use of digoxygenin-labelled Zip Nucleic Acid-modified oligonucleotides as probes for ISH. Significant differences in miRNAs' transcripts accumulation were evidenced between nitrate-supplied and nitrate-depleted roots. Real-time PCR analyses and in situ detection of miRNA confirmed the array data and allowed us to evidence distinct miRNAs spatio-temporal expression patterns in maize roots. Our results suggest that a prolonged nitrate depletion may induce post-transcriptionally the expression of target genes by repressing the transcription of specific miRNAs. In particular, the repression of the transcription of miR528a/b, miR528a*/b*, miR169i/j/k, miR169i*/j*/k*, miR166j/k/n and miR408/b upon nitrate shortage could represent a crucial step integrating nitrate signals into developmental changes in maize roots.
62 citations
TL;DR: It is demonstrated that PIN8, the closest member of the PIN family to PIN5, represents another ER-residing auxin transporter, and a role for PIN8 in intracellular auxin homeostasis is demonstrated.
Abstract: Cellular auxin homeostasis is controlled at many levels that include auxin biosynthesis, auxin metabolism, and auxin transport In addition to intercellular auxin transport, auxin homeostasis is modulated by auxin flow through the endoplasmic reticulum (ER) PIN5, a member of the auxin efflux facilitators PIN protein family, was the first protein to be characterized as an intracellular auxin transporter We demonstrated that PIN8, the closest member of the PIN family to PIN5, represents another ER-residing auxin transporter PIN8 is specifically expressed in the male gametophyte and is located in the ER By combining genetic, physiological, cellular and biochemical data we demonstrated a role for PIN8 in intracellular auxin homeostasis Although our investigation shed light on intracellular auxin transport in pollen, the physiological function of PIN8 still remains to be elucidated Here we discuss our data taking in consideration other recent findings
28 citations
TL;DR: This work proposes the use of Zm-p60.1 as a robust molecular tool that exploits the reversibility of O-glucosylation and enables delicate manipulations of active CK content at the cellular level.
20 citations
28 Aug 2012
TL;DR: A variational approach to simultaneously trace the axis and determine the thickness of 3-D (or 2-D) tubular structures defined by sparsely and unevenly sampled noisy surface points using a gradient descent scheme.
Abstract: We present a variational approach to simultaneously trace the axis and determine the thickness of 3-D (or 2-D) tubular structures defined by sparsely and unevenly sampled noisy surface points Many existing approaches try to solve the axis-tracing and the precise fitting in two subsequent steps In contrast to this our model is initialized with a small cylinder segment and converges to the final tubular structure in a single energy minimization using a gradient descent scheme The energy is based on the error of fit and simultaneously penalizes strong curvature and thickness variations We demonstrate the performance of this closed formulation on volumetric microscopic data sets of the Arabidopsis root tip, where only the nuclei of the cells are visible
7 citations