Vacuolar Proton Pyrophosphatase Is Required for High Magnesium Tolerance in <i>Arabidopsis</i>

• Main Authors: Yang Yang, Ren-Jie Tang, Baicong Mu, Ali Ferjani, Jisen Shi, Hongxia Zhang, Fugeng Zhao, Wen-Zhi Lan, Sheng Luan
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: International Journal of Molecular Sciences
• Subjects: vacuolar H⁺-pyrophosphatase; <i>AtAVP1</i>; cellular PPi homeostasis; high-Mg tolerance
• Online Access: https://www.mdpi.com/1422-0067/19/11/3617

Magnesium (Mg²⁺) is an essential nutrient in all organisms. However, high levels of Mg²⁺ in the environment are toxic to plants. In this study, we identified the vacuolar-type H⁺-pyrophosphatase, AVP1, as a critical enzyme for optimal plant growth under high-Mg conditions. The <i>Arabidopsis</i> <i>avp1</i> mutants displayed severe growth retardation, as compared to the wild-type plants upon excessive Mg²⁺. Unexpectedly, the <i>avp1</i> mutant plants retained similar Mg content to wild-type plants under either normal or high Mg conditions, suggesting that AVP1 may not directly contribute to Mg²⁺ homeostasis in plant cells. Further analyses confirmed that the <i>avp1</i> mutant plants contained a higher pyrophosphate (PPi) content than wild type, coupled with impaired vacuolar H⁺-pyrophosphatase activity. Interestingly, expression of the <i>Saccharomyces cerevisiae</i> cytosolic inorganic pyrophosphatase1 gene <i>IPP1</i>, which facilitates PPi hydrolysis but not proton translocation into vacuole, rescued the growth defects of <i>avp1</i> mutants under high-Mg conditions. These results provide evidence that high-Mg sensitivity in <i>avp1</i> mutants possibly resulted from elevated level of cytosolic PPi. Moreover, genetic analysis indicated that mutation of <i>AVP1</i> was additive to the defects in <i>mgt6</i> and <i>cbl2 cbl3</i> mutants that are previously known to be impaired in Mg²⁺ homeostasis. Taken together, our results suggest AVP1 is required for cellular PPi homeostasis that in turn contributes to high-Mg tolerance in plant cells.