Plant Trans-Golgi Network/Early Endosome pH regulation requires Cation Chloride Cotransporter (CCC1)

Abstract

Plant cells maintain a low luminal pH in the Trans-Golgi-Network/Early Endosome (TGN/EE), the organelle in which the secretory and endocytic pathways intersect. Impaired TGN/EE pH regulation translates into severe plant growth defects. The identity of the proton pump and proton/ion antiporters that regulate TGN/EE pH have been determined, but an essential component required to complete the TGN/EE membrane transport circuit remains unidentified - a pathway for cation and anion efflux. Here, we have used complementation, genetically encoded fluorescent sensors, and pharmacological treatments to demonstrate that Arabidopsis Cation Chloride Cotransporter (CCC1) is this missing component necessary for regulating TGN/EE pH and function. Loss of CCC1 function leads to alterations in TGN/EE-mediated processes including endocytic trafficking, exocytosis and response to abiotic stress, consistent with the multitude of phenotypic defects observed in ccc1 knockout plants. This discovery places CCC1 as a central component of plant cellular function.

Chromosome-level genomes of multicellular algal sisters to land plants illuminate signaling network evolution

“…Expanded signaling and transport, possibly related to filamentous growth, include calcium signaling (OG 56), zinc-induced facilitators (OG 258), cysteine-rich fibroblast growth factor receptors found in the Golgi apparatus (OG 518), and cation/H+ antiporters (OG 809). Cation/H+ antiporters are closely related to A. thaliana nhx5/nhx6 that act on pH and ion homeostasis in the endosome and are key for membrane trafficking in the trans-Golgi network (Bassil et al, 2011; McKay et al, 2022), and diverse developmental processes (Dragwidge et al, 2018). A dynein homolog (OG 72) was significantly contracted in Zygnematophyceae ( Table S3B ), which might be associated with cytokinesis of cilia and flagella and thus in line with the loss of motile gametes in Zygnematophyceae and Embryophyta (OG 72 was also identified as contracted in that ancestor).…”

Roles of type II H+-PPases and PPsPase1/PECP2 in early developmental stages and PPi homeostasis of Arabidopsis thaliana

“…Nevertheless, the respective importance of their combined functions (PPi hydrolysis coupled to proton pumping) still awaits demonstration of their impact on biological functions. As deletion of these transporters has no overall impact on PPi homeostasis, it will be important to characterize the impact of vhp2 mutations on Golgi pH maintenance, likely in combination with mutations of other known membrane-bound pH regulators present in the endomembrane network (McKay et al, 2022). Overall, a careful analysis of these mutants, particularly under stress conditions where PPi could be limiting, and where pH maintenance within the Golgi might be affected, is necessary to understand under which conditions the dual activity of these proteins (pyrophosphatase/proton pump) could become limiting.…”

Ion Changes and Signaling under Salt Stress in Wheat and Other Important Crops

“…pH regulation in a cell is dependent on the proton pump and antiporter activities, but other mechanisms are also needed. Recent findings suggest that CCC1, a cation-chloride cotransporter in Arabidopsis , is necessary for the regulation of pH in the Golgi-network early endosome [ 299 ]. If this regulation does not function, the plant cannot develop normally, it will obtain reduced size, chlorophyll defects, and stem necrosis and cannot respond to abiotic stress [ 42 ].…”