Sequential removal of cation/H+ exchangers reveals their additive role in elemental distribution, calcium depletion and anoxia tolerance

Authors: MATHEW, INY - Children'S Nutrition Research Center (CNRC); RHEIN, HORMAT - Children'S Nutrition Research Center (CNRC); YANG, JIAN - Children'S Nutrition Research Center (CNRC); GRADOGNA, ANTONELLA - Consiglio Nazionale Delle Ricerche; CARPANETO, ARMANDO - University Of Genoa; GUO, QI - Southern Cross University; TAPPERO, RYAN - Brookhaven National Laboratory; SCHOLZ-STARKE, JOACHIM - Consiglio Nazionale Delle Ricerche; BARKLA, BRONWYN - Southern Cross University; HIRSCHI, KENDAL - Children'S Nutrition Research Center (CNRC); PUNSHON, TRACY - Dartmouth College

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2023
Publication Date: 11/2/2023
Citation: Mathew, I.E., Rhein, H.S., Yang, J., Gradogna, A., Carpaneto, A., Guo, Q., Tappero, R., Scholz-Starke, J., Barkla, B., Hirschi, K.D., Punshon, T. 2023. Sequential removal of cation/H+ exchangers reveals their additive role in elemental distribution, calcium depletion and anoxia tolerance. Plant Cell and Environment. 47(2):557-573. https://doi.org/10.1111/pce.14756.
DOI: https://doi.org/10.1111/pce.14756

Interpretive Summary: This research delves into how certain plant proteins aid in substance movement, particularly in flooded conditions where oxygen levels drop. By studying these proteins, scientists found that plants with specific mutations grew slower but coped better with low oxygen levels, akin to conditions during flooding. Additionally, they learned that these proteins influence the levels of vital elements like calcium in plant leaves. Understanding the mechanics of these proteins could aid in developing flood-resistant plants, crucial for agriculture and environmental conservation efforts.

Technical Abstract: Multiple Arabidopsis H+/Cation exchangers (CAXs) participate in high-capacity transport into the vacuole. Previous studies have analysed single and double mutants that marginally reduced transport; however, assessing phenotypes caused by transport loss has proven enigmatic. Here, we generated quadruple mutants (cax1-4: qKO) that exhibited growth inhibition, an 85% reduction in tonoplast-localised H+/Ca transport, and enhanced tolerance to anoxic conditions compared to CAX1 mutants. Leveraging inductively coupled plasma mass spectrometry (ICP-MS) and synchrotron X-ray fluorescence (SXRF), we demonstrate CAX transporters work together to regulate leaf elemental content: ICP-MS analysis showed that the elemental concentrations in leaves strongly correlated with the number of CAX mutations; SXRF imaging showed changes in element partitioning not present in single CAX mutants and qKO had a 40% reduction in calcium (Ca) abundance. Reduced endogenous Ca may promote anoxia tolerance; wild-type plants grown in Ca-limited conditions were anoxia tolerant. Sequential reduction of CAXs increased mRNA expression and protein abundance changes associated with reactive oxygen species and stress signalling pathways. Multiple CAXs participate in postanoxia recovery as their concerted removal heightened changes in postanoxia Ca signalling. This work showcases the integrated and diverse function of H+/Cation transporters and demonstrates the ability to improve anoxia tolerance through diminishing endogenous Ca levels.