Expressed sequence-tag analysis of tobacco sperm cells reveals a unique transcriptional profile and selective persistence of paternal transcripts after fertilization.

Transcript analysis of male gametes of Nicotiana tabacum was conducted to gather gene expression data regarding the specialization of male germ cells and transmission of paternal transcripts during fertilization. We constructed a tobacco sperm cell cDNA library yielding 1,864 expressed sequence tags representing 1,050 clusters; 37.2% of these clusters have no homologs in GenBank, and 42% did not match any functionally classified protein. A comparative analysis of tobacco sperm transcripts with those of Arabidopsis and maize confirms that some genes are conserved in sperm specialization, while some are distinct to tobacco germline cells. Using reverse transcription-PCR (RT-PCR) of selected transcripts, we evaluated expression of sperm-obtained sequences in vegetative tissue, isolated egg cells, zygotes, and two-celled proembryos, identifying sperm cell-specific transcripts as potential markers for fertilization analysis. We further confirmed that two clusters of sperm transcripts were detected in zygotes about 10 h after fertilization, offering new examples of apparently paternally transmitted transcripts that may be involved in egg cell activation and/or early embryogenesis.