Frings, S. | Search bioRxiv

bioRxiv2024

MEDIATOR SUBUNIT 25 modulates ERFVII-controlled hypoxia responses in Arabidopsis

Flooding impairs plant growth through oxygen deprivation, which activates plant survival and acclimation responses. Low-oxygen responses are generally associated with activation of group VII ETHYLENE-RESPONSE FACTOR (ERFVII) transcription factors. However, mechanism and molecular components by which ERFVII factors initiate gene expression are not fully elucidated. Here, we show that the Mediator complex subunit AtMED25 is recruited by RELATED TO APETALA 2.2 (RAP2.2) and RAP2.12 to coordinate gene expression during hypoxia in Arabidopsis thaliana.. The med25 mutants display reduced low-oxygen stress tolerance. AtMED25 associates with several ERFVII-controlled hypoxia core genes and its loss impairs transcription under hypoxia due to decreasing RNA polymerase II recruitment. Protein complex pulldown assays demonstrate that the Mediator complex built around AtMED25 is adjusted under low-oxygen conditions. Moreover, during hypoxia, no functional cooperation between AtMED25 and the two subunits AtMED8 and AtMED16 occurs, contrasting previous observations made for other conditions. In addition, AtMED25 function under hypoxia is independent from ethylene signalling. Finally, a functional conservation at the molecular level was found for the MED25-ERFVII module between Arabidopsis thaliana and the monocot Oryza sativa, pointing to a potentially universal role of MED25 in enabling ERFVII-dependent transcript responses to hypoxia in plants.

plant biology↗

bioRxiv2019

Photoactivation of olfactory sensory neurons does not affect action potential conduction in individual trigeminal sensory axons innervating the rodent nasal cavity

Olfactory and trigeminal chemosensory systems reside in parallel within the mammalian nose. Psychophysical studies in people indicate that these two systems interact at a perceptual level. Trigeminal sensations of pungency mask odour perception, while olfactory stimuli can influence trigeminal signal processing tasks such as odour localization. While imaging studies indicate overlap in limbic and cortical somatosensory areas activated by nasal trigeminal and olfactory stimuli, there is also potential cross-talk at the level of the olfactory epithelium, the olfactory bulb and trigeminal brainstem. Here we focused on potential interactions between olfactory and trigeminal signaling in the nasal cavity. We first used a forced choice paradigm to ascertain whether trigeminal and olfactory stimuli could influence behavior in mice. Mice avoided water sources associated with volatile TRPV1 and TRPA1 irritants, however, this aversion was mitigated when combined with a pure odorant (rose fragrance, phenylethyl alcohol, PEA). To determine whether olfactory-trigeminal interactions within the nose could potentially account for this behavioral effect we recorded from single trigeminal sensory axons innervating the nasal epithelium using an isolated in vitro preparation. To circumvent non-specific effects of chemical stimuli, optical stimulation was used to excite olfactory sensory neurons in a mouse line expressing channel-rhodopsin under the olfactory marker protein. During photoactivation of olfactory sensory neurons there was no modulation of action potential conduction in individual trigeminal axons. Similarly, no evidence was found for trigeminal axon collateral branching that might serve as a conduit for cross-talk between the olfactory epithelium and olfactory dura mater. Using direct assessment of trigeminal signals emanating from the mouse nasal cavity we see no evidence for paracrine nor axon reflex mediated cross-talk between olfactory and trigeminal sensory systems in the nasal cavity.

neuroscience↗