Involvement of small RNAs in the regulation of vegetative phase change in plants

Isabel Bartrina (Graz): Since their discovery in Caenorhabditis elegans in 1993 small RNA molecules have been found across many eukaryotic organisms, ranging from plants to mammals. Small RNAs are categorized into several classes, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), based on their mode of biogenesis. Once processed from their precursor transcripts, the mature small RNAs associate with Argonaute proteins to repress the target transcripts. In plants, it is now clear that endogenous small RNAs play a crucial role in gene regulation during plant development. By targeting major transcription factors, small RNAs work as inhibition signals that can diffuse across tissues and therefore have a central role in various developmental networks. Probably the best characterized example is their role in regulating developmental timing. The exact timing of devel-opmental transitions is crucial for reproductive success. If executed in an untimely manner, the plant may lack the energy required to reproduce effectively because of a compromised leaf func-tion, or may reproduce when environmental conditions are not favorable. In this talk, I will high-light the role of miRNAs in the regulation of vegetative phase change and discuss how the plant hormone cytokinin adds to the complexity of the regulatory network controlling this phase transi-tion.