Interaction between Arabidopsis Ca2+/H+ Exchangers CAX1 and CAX3

Abstract

In plants, high capacity tonoplast cation/H؉ antiport is mediated in part by a family of CAX (cation exchanger) transporters. Functional association between CAX1 and CAX3 has previously been inferred; however, the nature of this interaction has not been established. Here we analyze the formation of "hetero-CAX" complexes and their transport properties. Co-expressing both CAX1 and CAX3 mediated lithium and salt tolerance in yeast, and these phenotypes could not be recapitulated by expression of deregulated versions of either transporter. Coincident expression of Arabidopsis CAX1 and CAX3 occurs during particular stress responses, flowering, and seedling growth. Analysis of cax1, cax3, and cax1/3 seedlings demonstrated similar stress sensitivities. When plants expressed high levels of both CAXs, alterations in transport properties were evident that could not be recapitulated by high level expression of either transporter individually. In planta coimmunoprecipitation suggested that a protein-protein interaction occurred between CAX1 and CAX3. In vivo interaction between the CAX proteins was shown using a split ubiquitin yeast two-hybrid system and gel shift assays. These findings demonstrate cation exchange plasticity through hetero-CAX interactions.

CAX‐ing a wide net: Cation/H+ transporters in metal remediation and abiotic stress signalling

“…Furthermore, the study of plant CAXs may be further challenged by the potential of homomeric and heteromeric CAX complexes exhibiting different functional properties (Zhao et al . 2009a,b). Therefore, the study of plant CAXs may require more imaginative approaches going forward.…”

“…CAXs from plants have previously been reported to form homomeric or indeed heteromeric oligomers, with potential implications for functional activity (Zhao et al . 2009a,b). Thus structural information may be able to provide further insight into the relevance of CAX complexes in the future.…”

Vacuolar Ca2+/H+ Transport Activity Is Required for Systemic Phosphate Homeostasis Involving Shoot-to-Root Signaling in Arabidopsis

“…CAX1 and CAX3 are tonoplast-localized Ca 2+ /H + antiporters that mediate the sequestration of Ca 2+ into the vacuole (Cheng et al, 2003(Cheng et al, , 2005. Knockout or overexpression of CAX1 or CAX3 alone in planta has been shown to result in perturbations in ion homeostasis and altered responses to salinity and cold stresses, while loss of both CAX1 and CAX3 led to a severe reduction in growth, leaf tip and flower necrosis, and a pronounced sensitivity to exogenous Ca 2+ and other ions (Hirschi, 1999;Catala et al, 2003;Cheng et al, 2003Cheng et al, , 2005Mei et al, 2007;Zhao et al, 2009). Intriguingly, alterations in transport properties resulting from overexpression of both CAXs in yeast could not be recapitulated by high-level expression of either transporter individually (Zhao et al, 2009).…”

“…Knockout or overexpression of CAX1 or CAX3 alone in planta has been shown to result in perturbations in ion homeostasis and altered responses to salinity and cold stresses, while loss of both CAX1 and CAX3 led to a severe reduction in growth, leaf tip and flower necrosis, and a pronounced sensitivity to exogenous Ca 2+ and other ions (Hirschi, 1999;Catala et al, 2003;Cheng et al, 2003Cheng et al, , 2005Mei et al, 2007;Zhao et al, 2009). Intriguingly, alterations in transport properties resulting from overexpression of both CAXs in yeast could not be recapitulated by high-level expression of either transporter individually (Zhao et al, 2009). It was postulated that the differential stress sensitivities of cax mutants are due to specific responses by CAX1 or CAX3 to individual stresses or to distinct transport properties conferred by hetero-CAX complexes formed by CAX1 and CAX3 (Cheng et al, 2005;Zhao et al, 2009).…”

“…Intriguingly, alterations in transport properties resulting from overexpression of both CAXs in yeast could not be recapitulated by high-level expression of either transporter individually (Zhao et al, 2009). It was postulated that the differential stress sensitivities of cax mutants are due to specific responses by CAX1 or CAX3 to individual stresses or to distinct transport properties conferred by hetero-CAX complexes formed by CAX1 and CAX3 (Cheng et al, 2005;Zhao et al, 2009). If we suppose that loss of the putative CAX1-CAX3 heteromer is Figure 5.…”