Browsing by Subject "Aquaporine"

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Die Bedeutung von AQUAPORIN INTERACTOR 1 (AQI1) für die Zelltodregulation in Pflanzen
(2014) Glink, Eva Katharina; Pfitzner, Artur J. P.
Programmed cell death (PCD) is an important process during development, senescence and pathogen defence in plants and in animals. It is a genetically regulated and targeted cell suicide of single cells, for benefit of the whole organism. In plants, PCD is of great importance, especially in the course of the “hypersensitive response” (HR). For protecting themselves against harmful intruders, infected plant cells are directly deposed of by PCD. The developing local lesions act as a barrier between host plant and pathogen. This prevents the systemic expansion of biotrophic pathogens within the whole plant. The induction of PCD involves complex signal transduction pathways. Reactive oxygen species (ROS), in particular H₂O₂, play an important role as signal molecules during PCD. The transport of H₂O₂ across cell membranes is conducted by aquaporins. As the vitality of cells depends on intracellular H₂O₂-levels, a spatiotemporal control of this H₂O₂-transport is indispensable. AQUAPORIN INTERACTOR 1 (AQI1) was isolated as a potential regulator of the channel function of aquaporins. AQI1 is a plant protein with sequence homology to the mammal aminoacylase 1. It is known, that aminoacylases catalyse the hydrolysis of acyl-amino acids. However, the physiological function of these enzymes is still unclear. This study represents the first characterisation of an aminoacylase (AQI1) in plants. The physiological function of AQI1 as a regulator of aquaporins, as well as the underlying molecular mechanisms, have been analysed. In addition to deacetylation of amino acids, a second function of the protein AQI1 was discovered. AQI1 interferes with the channel activity of aquaporins by protein-protein interaction. In this way, AQI1 is able to inhibit the H₂O₂-, and to a certain extent also the H₂O-influx, through aquaporins. Probably, this happens by blocking the aquaporinpore. Due to this function, AQI1 is a major component in cell death regulation in plants. During the „hypersensitive response“ (HR), which is induced as a result of pathogen attack, AQI1 accumulates to high levels to prevent the influx of toxic amounts of H₂O₂ into neighbouring cells. This ensures a local control of PCD. In addition, AQI1 seems to be involved in regulation of senescence processes. It could be demonstrated, that AQI1 accumulates in a gradient from juvenile to senescent leaves, due to degradation in older tissues. By this age-dependent accumulation, AQI1 could contribute to the vitality of leaves, by preventing the influx of excessive amounts of H₂O₂ into the cell.
PEP7 is a ligand for receptor kinase SIRK1 to regulate aquaporins and root growth
(2021) Wang, Jiahui; Schulze, Waltraud
Receptor kinases constitute the largest protein family in regulating various responses to external and internal biotic and abiotic signals. Functional characterization of this large protein family and particularly the identification of their ligands remains a major challenge in plant biology. Previously, we identified SIRK1 and QSK1 as a receptor / co-receptor pair involved in regulation of aquaporins in response to osmotic changes induced by sucrose. Here, we now identify a member of the Elicitor Peptide (PEP) family, namely PEP7, as a ligand to receptor kinase SIRK1. PEP7 was shown to bind to the extracellular domain of SIRK1 with a binding constant of 19 µM. PEP7 was secreted to the apoplasm specifically in response to sucrose. Formation of a signaling complex involving SIRK1, QSK1 as well as aquaporins as substrates was induced by sucrose or external PEP7 treatment. PEP7 induced aquaporin phosphorylation and water influx activity. The knock-out mutant of receptor SIRK1 was not responsive to external PEP7 treatment. Binding to receptor SIRK1 and induction of physiological responses was specific to PEP7, neither other members of the PEP-family (PEP6, PEP4), nor other small signaling peptides (CLEs, IDA, RALFs) induced SIRK1 kinase activity, aquaporin phosphorylation, or protoplast water influx activity.