Richard Immink, Wageningen University and Research Centre, The Netherlands
Lars Hennig, Plant Biology
Lecture hall A281, Uppsala BioCentre, Ultuna
14:00 - 15:00
Alternative splicing: a thermosensor in flowering time control?

As a consequence of a sessile lifestyle, plants are constantly faced with changing environments. In order to profit maximally from good environmental conditions and to protect from harsh conditions, plants developed ways to sense and react to environmental signals, including ambient temperature fluctuations.
Small changes in ambient temperature can have major effects on plant architecture, resistance to pathogens, and flowering time [1]. Flowering is a key event in a plant’s life cycle, because of its impact on reproductive success and hence, survival of the species.
Because environmental conditions are highly variable, plants need a molecular mechanism that can quickly react and establish adaptation to a new situation. It often has been suggested that alternative splicing (AS), the molecular mechanism by which more than one messenger RNA (mRNA) can be produced from a single gene, plays a pivotal role in this signal transduction cascade and adaptation to environmental changes [2]. We analysed ambient temperature-directed AS events that occur within one-to-five days after a temperature switch, using Illumina HiSeq sequencing. We show that flowering time genes are overrepresented amongst the ambient temperature induced AS genes, indicating that AS is one of the potential mechanisms by which plants are able to sense temperature and adapt floral timing. However, analysis of our dataset disclosed an even stronger overrepresentation of splicing-related genes, of which almost ten percent showed differential AS upon ambient temperature shifts in the Col-0 ecotype of A. thaliana. Splicing related genes encode the proteins making up the spliceosome, a large cellular machinery that executes the splicing reactions. Therefore, we hypothesize a two-step splicing system upon perception of ambient temperature changes by the plant: In the first step, splicing related genes are alternatively spliced, resulting in a different composition of the spliceosome. In the second step, AS of genes regulating the ambient temperature response of the plant takes place as a consequence of the altered spliceosomal composition. Hence, the AS machinery appears as one of the candidates for the long-sought thermosensors in plants.
We have studied specifically temperature-dependent AS of the floral repressor FLOWERING LOCUS M (FLM), showing a key function for this MADS box transcription factor in the ambient temperature response [3,4]. However, why splicing of this particular gene and a subset of other genes is temperature-sensitive remains elusive. We found that changes in the epigenome, more specifically reduced H3K36me3, impairs the ability of plants to respond with an altered flowering time upon changing ambient temperatures. In addition, preliminary results suggest a higher level of H3K36me3 in genes undergoing AS upon ambient temperature fluctuations. In parallel, we investigated the potential role of Long Non-coding RNA’s (LncRNAs) in this process and latest results will be discussed.
Understanding how plants measure temperature and integrate this information in their developmental programs at the molecular level is essential and our studies reveal the complexity of this regulation.

1.    Verhage, L., Angenent, G.C., Immink, R.G.H. (2014). Research on floral timing by ambient temperature comes into blossom. Trends in Plant Sci, 10.1016/j.tplants.2014.03.009.
2.    Capovilla, G., Pajoro, A., Immink, R.G.H., and Schmid, M. (2015). Role of alternative pre-mRNA splicing in temperature signalling. Curr Opin Plant Biol 27, 97-103.
3.    Severing, E.I., van Dijk, A.D.J., Morabito, G., Busscher-Lange, J., Immink, R.G.H., and van Ham, R.C.H.J. (2012). The impact of alternative splicing on plant MADS domain protein function. PLoS One 7(1):e30524.
4.    Posé, D., Verhage, L., Ott, F., Yant, L., Mathieu, J., Angenent, G.C., Immink, R.G.H., and Schmid, M. (2013). Temperature-dependent regulation of flowering by antagonistic FLM variants. Nature, doi:10.1038/nature12633