Microarray analysis reveals altered expression of a large number of nuclear genes in developing cytoplasmic male sterile Brassica napus flowers

Authors

  • Jenny Carlsson,

    Corresponding author
    1. Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE-750 07 Uppsala, Sweden
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    • These authors contributed equally to this study.

  • Ulf Lagercrantz,

    1. Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE-750 07 Uppsala, Sweden
    2. Uppsala University, Evolutionary Functional Genomics, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
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    • These authors contributed equally to this study.

  • Jens Sundström,

    1. Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE-750 07 Uppsala, Sweden
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  • Rita Teixeira,

    1. Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE-750 07 Uppsala, Sweden
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    • Present address: Section of Plant Biology, UC Davis, One Shields Avenue, Davis, CA 95616, USA.

  • Frank Wellmer,

    1. Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, USA
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    • §

      Present address: Department of Genetics, Smurfit Institute, Trinity College Dublin, Dublin 2, Ireland.

  • Elliot M. Meyerowitz,

    1. Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125, USA
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  • Kristina Glimelius

    1. Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE-750 07 Uppsala, Sweden
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(fax +46 18 67 32 79; e-mail jenny.carlsson@vbsg.slu.se).

Summary

To gain new insights into the mechanism underlying cytoplasmic male sterility (CMS), we compared the nuclear gene expression profiles of flowers of a Brassica napus CMS line with that of the fertile B. napus maintainer line using Arabidopsis thaliana flower-specific cDNA microarrays. The CMS line used has a B. napus nuclear genome, but has a rearranged mitochondrial (mt) genome consisting of both B. napus and A. thaliana DNA. Gene expression profiling revealed that a large number of genes differed in expression between the two lines. For example, nuclear genes coding for proteins that are involved in protein import into organelles, genes expressed in stamens and pollen, as well as genes implicated in either cell-wall remodeling or architecture, were repressed in the CMS line compared with B. napus. These results show that the mt genome of the CMS line strongly influences nuclear gene expression, and thus reveal the importance of retrograde signalling between the mitochondria and the nucleus. Furthermore, flowers of the CMS line are characterized by a replacement of stamens with carpelloid organs, and thus partially resemble the APETALA3 (AP3) and PISTILLATA (PI) mutants. In accordance with this phenotype, AP3 expression was downregulated in the stamens, shortly before these organs developed carpelloid characteristics, even though it was initiated correctly. Repression of PI succeeded that of AP3 and might be a consequence of a loss of AP3 activity. These results suggest that AP3 expression in stamens depends on proper mt function and a correct nuclear–mt interaction, and that mt alterations cause the male sterility phenotype of the CMS line.

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