Vacuolar Ca2+/H+ transport activity is required for systemic phosphate homeostasis involving shoot-to-root signaling in Arabidopsis |
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Authors: | Liu Tzu-Yin Aung Kyaw Tseng Ching-Ying Chang Tzu-Yun Chen Ying-Shin Chiou Tzyy-Jen |
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Institution: | Agricultural Biotechnology Research Center (T.-Y.L., K.A., C.-Y.T., T.-Y.C., Y.-S.C, T.-J.C.) and Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program (K.A., T.-J.C.), Academia Sinica, Taipei 115, Taiwan; Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan (T.-J.C.) |
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Abstract: | Calcium ions (Ca(2+)) and Ca(2+)-related proteins mediate a wide array of downstream processes involved in plant responses to abiotic stresses. In Arabidopsis (Arabidopsis thaliana), disruption of the vacuolar Ca(2+)/H(+) transporters CAX1 and CAX3 causes notable alterations in the shoot ionome, including phosphate (P(i)) content. In this study, we showed that the cax1/cax3 double mutant displays an elevated P(i) level in shoots as a result of increased P(i) uptake in a miR399/PHO2-independent signaling pathway. Microarray analysis of the cax1/cax3 mutant suggests the regulatory function of CAX1 and CAX3 in suppressing the expression of a subset of shoot P(i) starvation-responsive genes, including genes encoding the PHT1;4 P(i) transporter and two SPX domain-containing proteins, SPX1 and SPX3. Moreover, although the expression of several PHT1 genes and PHT1;1/2/3 proteins is not up-regulated in the root of cax1/cax3, results from reciprocal grafting experiments indicate that the cax1/cax3 scion is responsible for high P(i) accumulation in grafted plants and that the pht1;1 rootstock is sufficient to moderately repress such P(i) accumulation. Based on these findings, we propose that CAX1 and CAX3 mediate a shoot-derived signal that modulates the activity of the root P(i) transporter system, likely in part via posttranslational regulation of PHT1;1 P(i) transporters. |
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