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The Arabidopsis Plastidic Glucose 6-Phosphate/Phosphate Translocator GPT1 Is Essential for Pollen Maturation and Embryo Sac Development

^a Botanisches Institut der Universität zu Köln, D-50931 Köln, Germany
^b Biologie/Elektronenmikroskopie NW I/B1, Universität Bayreuth, D-95447 Bayreuth, Germany
^c Zentrum für Molekularbiologie der Pflanzen, Universität Tübingen, D-72076 Tübingen, Germany
^d Max-Planck-Institut für Züchtungsforschung, D-50928 Köln, Germany
^e Julius-von-Sachs Institut für Biowissenschaften, Universität Würzburg, D-97082 Würzburg, Germany

² To whom correspondence should be addressed. E-mail anja.schneider{at}uni-koeln.de; fax 49-221-4705039.

Plastids of nongreen tissues can import carbon in the form of glucose 6-phosphate via the glucose 6-phosphate/phosphate translocator (GPT). The Arabidopsis thaliana genome contains two homologous GPT genes, AtGPT1 and AtGPT2. Both proteins show glucose 6-phosphate translocator activity after reconstitution in liposomes, and each of them can rescue the low-starch leaf phenotype of the pgi1 mutant (which lacks plastid phosphoglucoisomerase), indicating that the two proteins are also functional in planta. AtGPT1 transcripts are ubiquitously expressed during plant development, with highest expression in stamens, whereas AtGPT2 expression is restricted to a few tissues, including senescing leaves. Disruption of GPT2 has no obvious effect on growth and development under greenhouse conditions, whereas the mutations gpt1-1 and gpt1-2 are lethal. In both gpt1 lines, distorted segregation ratios, reduced efficiency of transmission in males and females, and inability to complete pollen and ovule development were observed, indicating profound defects in gametogenesis. Embryo sac development is arrested in the gpt1 mutants at a stage before the fusion of the polar nuclei. Mutant pollen development is associated with reduced formation of lipid bodies and small vesicles and the disappearance of dispersed vacuoles, which results in disintegration of the pollen structure. Taken together, our results indicate that GPT1-mediated import of glucose 6-phosphate into nongreen plastids is crucial for gametophyte development. We suggest that loss of GPT1 function results in disruption of the oxidative pentose phosphate cycle, which in turn affects fatty acid biosynthesis.

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