Heterodimerization of Arabidopsis calcium/proton exchangers contributes to regulation of guard cell dynamics and plant defense responses.

Arabidopsis thaliana cation exchangers (CAX1 and CAX3) are closely related tonoplast-localized calcium/proton (Ca2+/H+) antiporters that contribute to cellular Ca2+ homeostasis. CAX1 and CAX3 were previously shown to interact in yeast; however, the function of this complex in plants has remained elusive. Here, we demonstrate that expression of CAX1 and CAX3 occurs in guard cells. Additionally, CAX1 and CAX3 are co-expressed in mesophyll tissue in response to wounding or flg22 treatment, due to the induction of CAX3 expression. Having shown that the transporters can be co-expressed in the same cells, we demonstrate that CAX1 and CAX3 can form homomeric and heteromeric complexes in plants. Consistent with the formation of a functional CAX1-CAX3 complex, CAX1 and CAX3 integrated into the yeast genome suppressed a Ca2+-hypersensitive phenotype of mutants defective in vacuolar Ca2+ transport, and demonstrated enzyme kinetics different from those of either CAX protein expressed by itself. We demonstrate that the interactions between CAX proteins contribute to the functioning of stomata, because stomata were more closed in cax1-1, cax3-1, and cax1-1/cax3-1 loss-of-function mutants due to an inability to buffer Ca2+ effectively. We hypothesize that the formation of CAX1-CAX3 complexes may occur in the mesophyll to affect intracellular Ca2+ signaling during defense responses

The sodium transporter encoded by the HKT1;2 gene modulates sodium/potassium homeostasis in tomato shoots under salinity

[EN] Excessive soil salinity diminishes crop yield and quality. In a previous study in tomato, we identified two closely linked genes encoding HKT1-like transporters, HKT1;1 and HKT1;2, as candidate genes for a major quantitative trait locus (kc7.1) related to shoot Na+/K+ homeostasis - a major salt tolerance trait - using two populations of recombinant inbred lines (RILs). Here, we determine the effectiveness of these genes in conferring improved salt tolerance by using two near-isogenic lines (NILs) that were homozygous for either the Solanum lycopersicum allele (NIL17) or for the Solanum cheesmaniae allele (NIL14) at both HKT1 loci; transgenic lines derived from these NILs in which each HKT1;1 and HKT1;2 had been silenced by stable transformation were also used. Silencing of ScHKT1;2 and SlHKT1;2 altered the leaf Na+/K+ ratio and caused hypersensitivity to salinity in plants cultivated under transpiring conditions, whereas silencing SlHKT1;1/ScHKT1;1 had a lesser effect. These results indicate that HKT1;2 has the more significant role in Na+ homeostasis and salinity tolerance in tomato.We thank Dr Espen Granum for critically reading the manuscript, Maria Isabel Gaspar Vidal and Elena Sanchez Romero for technical assistance, the Instrumental Technical Service at EEZ-CSIC for DNA sequencing and ICP-OES mineral analysis and Michael O'Shea for proofreading the text. In addition, we thank Dr Ana P. Ortega who assisted in preliminary experiments. This work was supported by ERDF-cofinanced grants, AGL2010-17090 and AGL2013-41733-R (A.B.), AGL2015-64991-C3-3-R (V.M.) and AGL2014-56675-R (M.J.A.) from the Spanish "Ministerio de Economia, Industria y Competitividad'; CVI-7558, Proyecto de Excelencia, from Junta de Andalucia (A.B); and the Australian Research Council (ARC) for Centre of Excellence (CE14010008) and Future Fellowship (FT130100709) funding (M.G.). N.J-P. was supported by an FPI program BES-2011-046096 and her stay in M.G.'s lab by a short-stay EEBB-I-14-08682, both from the Spanish from "Ministerio de Economia Industria y Competitividad'. The authors have no conflict of interest to declare.Jaime-Perez, N.; Pineda Chaza, BJ.; García Sogo, B.; Atarés Huerta, A.; Athman, A.; Byrt, CS.; Olias, R.... (2017). The sodium transporter encoded by the HKT1;2 gene modulates sodium/potassium homeostasis in tomato shoots under salinity. Plant Cell & Environment. 40(5):658-671. https://doi.org/10.1111/pce.12883S65867140

Cell-Specific Vacuolar Calcium Storage Mediated by CAX1 Regulates Apoplastic Calcium Concentration, Gas Exchange, and Plant Productivity in Arabidopsis[W][OA]

Mineral elements are often preferentially stored in vacuoles of specific leaf cell types, but the mechanism and physiological role for this phenomenon is poorly understood. We use single-cell analysis to reveal the genetic basis underpinning mesophyll-specific calcium storage in Arabidopsis leaves and a variety of physiological assays to uncover its fundamental importance to plant productivity

Heterodimerization of Arabidopsis calcium/proton exchangers contributes to regulation of guard cell dynamics and plant defense responses

Arabidopsis thaliana cation exchangers (CAX1 and CAX3) are closely related tonoplast-localized calcium/proton (Ca2+/H+) antiporters that contribute to cellular Ca2+ homeostasis. CAX1 and CAX3 were previously shown to interact in yeast; however, the function of this complex in plants has remained elusive. Here, we demonstrate that expression of CAX1 and CAX3 occurs in guard cells. Additionally, CAX1 and CAX3 are co-expressed in mesophyll tissue in response to wounding or flg22 treatment, due to the induction of CAX3 expression. Having shown that the transporters can be co-expressed in the same cells, we demonstrate that CAX1 and CAX3 can form homomeric and heteromeric complexes in plants. Consistent with the formation of a functional CAX1-CAX3 complex, CAX1 and CAX3 integrated into the yeast genome suppressed a Ca2+-hypersensitive phenotype of mutants defective in vacuolar Ca2+ transport, and demonstrated enzyme kinetics different from those of either CAX protein expressed by itself. We demonstrate that the interactions between CAX proteins contribute to the functioning of stomata, because stomata were more closed in cax1-1, cax3-1, and cax1-1/cax3-1 loss-of-function mutants due to an inability to buffer Ca2+ effectively. We hypothesize that the formation of CAX1-CAX3 complexes may occur in the mesophyll to affect intracellular Ca2+ signaling during defense responses

Wheat grain yield on saline soils is improved by an ancestral Na+ transporter gene

The ability of wheat to maintain a low sodium concentration ([Na+]) in leaves correlates with improved growth under saline conditions1,2. This trait, termed Na+ exclusion, contributes to the greater salt tolerance of bread wheat relative to durum wheat3,4. To improve the salt tolerance of durum wheat, we explored natural diversity in shoot Na+ exclusion within ancestral wheat germplasm. Previously, we showed that crossing of Nax2, a gene locus in the wheat relative Triticum monococcum into a commercial durum wheat (Triticum turgidum ssp. durum var. Tamaroi) reduced its leaf [Na+] (ref. 5). Here we show that a gene in the Nax2 locus, TmHKT1;5-A, encodes a Na+-selective transporter located on the plasma membrane of root cells surrounding xylem vessels, which is therefore ideally localized to withdraw Na+ from the xylem and reduce transport of Na+ to leaves. Field trials on saline soils demonstrate that the presence of TmHKT1;5-A significantly reduces leaf [Na+] and increases durum wheat grain yield by 25% compared to near-isogenic lines without the Nax2 locus.Rana Munns, Richard A. James, Bo Xu, Asmini Athman, Simon J. Conn, Charlotte Jordans, Caitlin S. Byrt, Ray A. Hare, Stephen D. Tyerman, Mark Tester, Darren Plett and Matthew Gilliha