The silent machinery behind gene modulation in sexual reproduction
The EU-funded SRSR (Deciphering small RNA mechanisms during sexual reproduction in Arabidopsis) project has investigated one potential stage director in the sexual reproductive process – RNA silencing mechanisms. An ancient system used by plants, animals and fungi, RNA silencing is an effective way to modulate gene expression. Recent research has established a clear link in the model plant Arabidopsis, between silencing small RNAs (sRNAs) and chromatin via RNA directed DNA methylation (RdDM). However, relatively little is known about the involvement of sRNAs in the reproductive process. To track events in the silencing machinery, the researchers constructed transgenic Arabidopsis plants with transcriptional fluorescent reporters for all ten Argonaut (AGO) proteins and four Dicers. Analysis showed that most AGOs are expressed mainly in the egg cell and embryo but not in the endosperm food supply. The movements of sRNA were tracked using fluorescence reporting. Results point towards movement of the sRNA being so limited that it does not reach reproductive organs in sufficient quantity to silence tissue proteins. During SRSR work, the team discovered a new AGO. Expressed specifically at phloem termination of flowers, stamens, ovules and seeds, AGO3 is the subject of a paper published in Nature plants. Results showed that AGO3 is likely to be involved in post-transcriptional gene silencing rather than at the transcription stage. Further investigation showed a link with active translation in elongation. Overall, research indicates that AGO3 regulates gene expression by a novel RNA-silencing pathway. SRSR research could have a profound impact on agriculture because understanding hybrid vigour and species compatibility are key areas in plant breeding. In the Arabidopsis research arena, a substantial knowledge platform on cell biology and reproduction has been constructed using tools such as imaging and protein fluorescence techniques.
Keywords
Sexual reproduction, Arabidopsis, RNA silencing, AGO, plant breeding
