1. ¹College of Life Science, Hunan Normal University, Changsha 410081, China
2. ²College of Life Science, Capital Normal University, Beijing 100037, China
3. ³Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720,USA

Correspondence: Dong-ping Li, Fax: 86-731-887-2724
E-mail: dongbing_lee@yahoo.com.cn; Sheng Luan, Fax: 1-510-642-4995
E-mail: sluan@nature.berkeley.edu

^*These two authors contributed equally to this work.

Received 5 August 2008; Revised 10 October 2008; Accepted 17 February 2009.

Abstract

Magnesium (Mg²⁺) is abundant in plant cells and plays a critical role in many physiological processes. A 10-member gene family AtMGT (also known as AtMRS2) was identified in Arabidopsis, which belongs to a eukaryote subset of the CorA superfamily, functioning as Mg²⁺ transporters. Some family members (AtMGT1 and AtMGT10) function as high-affinity Mg²⁺ transporter and could complement bacterial mutant or yeast mutant lacking Mg²⁺ transport capability. Here we report an AtMGT family member, AtMGT9, that functions as a low-affinity Mg²⁺ transporter, and is essential for pollen development. The functional complementation assay in Salmonella mutant strain MM281 showed that AtMGT9 is capable of mediating Mg²⁺ uptake in the sub-millimolar range of Mg²⁺. The AtMGT9 gene was expressed most strongly in mature anthers and was also detectable in vascular tissues of the leaves, and in young roots. Disruption of AtMGT9 gene expression resulted in abortion of half of the mature pollen grains in heterozygous mutant +/mgt9, and no homozygous mutant plant was obtained in the progeny of selfed +/mgt9 plants. Transgenic plants expressing AtMGT9 in these heterozygous plants can recover the pollen phenotype to the wild type. In addition, AtMGT9 RNAi transgenic plants also showed similar abortive pollen phenotype to mutant +/mgt9. Together, our results demonstrate that AtMGT9 functions as a low-affinity Mg²⁺ transporter that plays a crucial role in male gametophyte development and male fertility.