Biology subjects

Meissner, G.

Publications and source records attributed to Meissner, G..

3 recordsLinked to original sources

bioRxiv2020

Vacuolar sucrose homeostasis is critical for development, seed properties and survival of dark phases of Arabidopsis

Although we know that most of the cellular sucrose is present in the cytosol and vacuole, our knowledge on the impact of this sucrose compartmentation on plant properties is still fragmentary. Here we attempted to alter the intracellular sucrose compartmentation of Arabidopsis mesophyll cells by either, overexpression of the vacuolar sucrose loader BvTST2.1 or by generation of mutants with decreased vacuolar invertase activity (amiR vi1-2). Surprisingly, BvTST2.1 overexpression led to increased monosaccharide levels in leaves, while sucrose remained constant. Latter observation allows the conclusion, that vacuolar invertase activity in mesophyll vacuoles exceeds sucrose uptake in Arabidopsis, which gained independent support by analyses on tobacco leaves transiently overexpressing BvTST2.1 and the invertase inhibitor NbVIF. However, we observed strongly increased sucrose levels in leaf extracts from independent amiR vi1-2 lines and non-aqueous fractionations confirmed that sucrose accumulation in corresponding vacuoles. amiR vi1-2 lines exhibited impaired early development and decreased weight of seeds. When germinated in the dark, mutant seedlings showed problems to convert sucrose into monosaccharides. Cold temperatures induced marked downregulation of the expression of both VI genes, while frost tolerance of amiR vi1-2 mutants was similar to WT indicating that increased vacuolar sucrose levels fully compensate for low monosaccharide concentrations. HighlightVacuolar sucrose accumulation in Arabidopsis is limited by high invertase activity and disturbed vacuolar sucrose homeostasis impairs plant germination, development, seed properties and survival under darkness.

plant biology↗

bioRxiv2019

Mapping Co-regulation Pathways among Ligand Binding sites in RyR1

Ryanodine receptor 1 (RyR1) is an intracellular calcium (Ca2+) release channel required for skeletal muscle contraction. RyR1 is co-regulated by multiple activators - Ca2+, ATP and caffeine (CFF), yet the mechanism of co-regulation and the action synergy of these activators is unknown. Here, we report the detailed network of allosteric connections between the three ligand sites and the pore region in (i) Ca2+ bound - closed, (ii) ATP/CFF bound - closed, (iii) Ca2+/ATP/CFF bound - closed and (iv) Ca2+/ATP/CFF bound - open RyR1 states. We find that two dominant paths mediate the communication between the Ca2+ binding site and pore region in Ca2+-only state. ATP/CFF-only occupied - closed RyR1 has two additional paths with CFF-but not ATP-occupied path using part of the closed Ca2+-only pathway. In the presence of Ca2+, ATP and CFF, major differences between the open and closed states are identified with both using part of the paths of the closed Ca2+-only and ATP/CFF-only states. We find that the three activators Ca2+, ATP, and CFF propagate their effects to the pore region through a network of partially overlapping pathways. Such coordination of allosteric pathway underlies the molecular basis of synergy of channel regulation by multiple activators.\n\nStatement of SignificanceRyRs are a group of Ca2+ channels that bind to several endogenous modulators and regulate Ca2+ release through closed-to-open gating transition. Despite the high-resolution structural data available for RyR1, the allosteric mechanism of RyR1 gating remains elusive. In this study, we employed graph-theoretical approach to demonstrate the allosteric network of synergistic interaction among various activators in RyR1. To our knowledge, for the first time we were able to identify the co-regulation among ligand sites in RyR1 to regulate the closed-to-open gating transition. The explored allosteric coupling in RyR1 may assist in designing advanced therapeutics for several debilitating diseases. Our findings in this study will assist to design new strategies for controlled allosteric regulation of RyR1 functionality in future.

biophysics↗

bioRxiv2018

Neurogenetic dissection of the Drosophila innate olfactory processing center

Animals exhibit innate behaviours in response to a variety of sensory stimuli such as olfactory cues. In Drosophila, a higher olfactory centre called the lateral horn (LH) is implicated in innate behaviour. However, our knowledge of the structure and function of the LH is scant, due to the lack of sparse neurogenetic tools for this brain region. Here we generate a collection of split-GAL4 driver lines providing genetic access to 82 LH cell-types. We identify the neurotransmitter and axo-dendritic polarity for each cell-type. Using these lines were create an anatomical map of the LH. We found that [~]30% of LH projections converge with outputs from the mushroom body, the site of olfactory learning and memory. Finally, using optogenetic activation of small groups of LH neurons. We identify cell-types that drive changes in either valence or specific motor programs, such as turning and locomotion. In summary we have generated a resource for manipulating and mapping LH neurons in both light and electron microscopy and generated insights into the anatomy and function of the LH.

neuroscience↗