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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Comparative Transcriptomics of Arabidopsis Sperm Cells^1,[C],[W]

Instituto Gulbenkian de Ciência, Centro de Biologia do Desenvolvimento, Oeiras, 2780–901, Portugal (F.B., G.G., R.G., N.M., J.A.F., J.D.B.); Plant Gene Expression Center, United States Department of Agriculture/Agricultural Research Service, University of California, Berkeley, Albany, California 94710 (S.M.); and Depto. Biologia Vegetal, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Lisbon, 1700, Portugal (J.A.F.)

In flowering plants, the two sperm cells are embedded within the cytoplasm of the growing pollen tube and as such are passively transported to the embryo sac, wherein double fertilization occurs upon their release. Understanding the mechanisms and conditions by which male gametes mature and take part in fertilization are crucial goals in the study of plant reproduction. Studies of gene expression in male gametes of maize (Zea mays) and Plumbago and in lily (Lilium longiflorum) generative cells already showed that the previously held view of transcriptionally inert male gametes was not true, but genome-wide studies were lacking. Analyses in the model plant Arabidopsis (Arabidopsis thaliana) were hindered, because no method to isolate sperm cells was available. Here, we used fluorescence-activated cell sorting to isolate sperm cells from Arabidopsis, allowing GeneChip analysis of their transcriptome at a genome-wide level. Comparative analysis of the sperm cell transcriptome with those of representative sporophytic tissues and of pollen showed that sperm has a distinct and diverse transcriptional profile. Functional classifications of genes with enriched expression in sperm cells showed that DNA repair, ubiquitin-mediated proteolysis, and cell cycle progression are overrepresented Gene Ontology categories. Moreover, analysis of the small RNA and DNA methylation pathways suggests that distinct mechanisms might be involved in regulating the epigenetic state of the paternal genome. We identified numerous candidate genes whose involvement in sperm cell development and fertilization can now be directly tested in Arabidopsis. These results provide a roadmap to decipher the role of sperm-expressed proteins.

² Present address: Centro de Engenharia Biológica e Química, Instituto Superior Técnico, Av. Rovisco Pais, 1049–001 Lisboa, Portugal.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: José A. Feijó (jfeijo{at}igc.gulbenkian.pt).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.125229

^* Corresponding author; e-mail jfeijo{at}igc.gulbenkian.pt.

Received June 23, 2008; accepted July 27, 2008; published July 30, 2008.

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Plant Physiol. 2008 148: 671-672. [Full Text]