Developmental and Structural Section
Gou, Xiaoping , Yuan, Tong , Wei, Xiaoping , Zhang, Jinghua , Li, Jia , Russell, Scott .
Molecular dissection of male germ lineage-specific promoters reveals multiple regulatory motifs.
In the flowering plant Plumbago zeylanica, the two sperm cells are dimorphic, with each one having a distinct expressional profile that is related to its ultimate fate during fertilization (Gou et al., 2009). Because this transcription is regulated through distinctive nucleotide sequences in the upstream promoter, we recovered one promoter sequence from a gene expressed by the sperm cell associated with the vegetative nucleus, specifically PzIPT1 and a promoter sequence from the other sperm cell (Sua),specifically PzSua62. To express these genes and examine their control, we fused the upstream regulatory region of each gene to a transgenic reporter construct consisting of either GFP or GUS in Arabidopsis and tobacco, as Plumbago transformation has proven recalcitrant. Interestingly,the 1.1k PzIPT1 promoter sequence and the PzSua62 promoter was conserved in the male germ lineage, but in Arabidopsis,both sperm cells displayed equal degrees of reporter. In tobacco, however, which is a bicellular pollen species, activity instead appeared in the vegetative cell until pollen germination,but did not occur in the male germ line. Truncation analyses of the promoter indicate that the expression strength in sperm cells decreases when the promoter is progressively truncated. Since truncation did not result in loss of cell specificity, we concluded that sperm cell-specific expression of PzIPT1 promoter is independent of the previously reported Germline Restrictive Silencer Factor (GRSF) binding site. This finding confirmed that specificity of sperm expression in PzIPT1 and PzSUA62 is not exclusively controlled by the action of a repressive protein, but by cell-type selective transcriptional enhancement. Interestingly, the PzIPT1 gene displays a potential motif for cytokinin-dependent protein binding. When transformed into Arabidopsis, expression in sperm cells responds to increases in cytokinin level with enhanced expression. Since PzIPT1 encodes an isopentenyl transferase - purported to be a control enzyme for cytokinin synthesis - increases in gene activity with the addition of exogenous cytokinin suggests a feed-forward mechanism for cytokinin generation. Interestingly, the sperm cell that possess this activity fuses with the endosperm in Plumbago. Since the promoters do not confer specifically to just one of the two sperm cells in the pollen, but did upregulate male germline expression equally in Arabidopsis, apparently multiple mechanisms regulate male germline cell gene expression in flowering plants.
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2 - University of Oklahoma, Department of Botany and Microbiology, Norman, OK, 730000
3 - University of Oklahoma, Department of Botany and Microbiology, Norman, OK, 73019
4 - Lanzhou University, School of Life Sciences, Lanzhou, Gansu, 730000, China
5 - University Of Oklahoma, Department Of Botany And Microbiology, 770 Van Vleet Oval, Norman, OK, 73019-6155, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Union D/Hyatt
Date: Monday, July 9th, 2012
Time: 4:00 PM