Plant Physiology 138:1232-1246 (2005)
© 2005 American Society of Plant Biologists
BREAKTHROUGH TECHNOLOGIES
Engineering Cytoplasmic Male Sterility via the Chloroplast Genome by Expression of -Ketothiolase1
Oscar N. Ruiz2 and
Henry Daniell*
Department of Molecular Biology and Microbiology, University of Central Florida, Orlando, Florida 328162364
While investigating expression of the polydroxybutyrate pathway in transgenic chloroplasts, we addressed the specific role of -ketothiolase. Therefore, we expressed the phaA gene via the chloroplast genome. Prior attempts to express the phaA gene in transgenic plants were unsuccessful. We studied the effect of light regulation of the phaA gene using the psbA promoter and 5' untranslated region, and evaluated expression under different photoperiods. Stable transgene integration into the chloroplast genome and homoplasmy were confirmed by Southern analysis. The phaA gene was efficiently transcribed in all tissue types examined, including leaves, flowers, and anthers. Coomassie-stained gel and western blots confirmed hyperexpression of -ketothiolase in leaves and anthers, with proportionately high levels of enzyme activity. The transgenic lines were normal except for the male-sterile phenotype, lacking pollen. Scanning electron microscopy revealed a collapsed morphology of the pollen grains. Floral developmental studies revealed that transgenic lines showed an accelerated pattern of anther development, affecting their maturation, and resulted in aberrant tissue patterns. Abnormal thickening of the outer wall, enlarged endothecium, and vacuolation affected pollen grains and resulted in the irregular shape or collapsed phenotype. Reversibility of the male-sterile phenotype was observed under continuous illumination, resulting in viable pollen and copious amount of seeds. This study results in the first engineered cytoplasmic male-sterility system in plants, offers a new tool for transgene containment for both nuclear and organelle genomes, and provides an expedient mechanism for F1 hybrid seed production.
1 This work was supported in part by the National Institutes of Health (grant no. R 01 GM 63879 to H.D.), the U.S. Department of Agriculture (grant no. 36112100001700D to H.D.), and Metabolix (grants to H.D.).
2 Present address: Midwest Research Institute, 1470 Treeland Blvd., S.E. Palm Bay, FL 329092211.
www.plantphysiol.org/cgi/doi/10.1104/pp.104.057729.
* Corresponding author; e-mail daniell{at}mail.ucf.edu; fax 4078230956.
Received December 7, 2004;
returned for revision February 21, 2005;
accepted March 14, 2005.
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