As winter winds turn our noses into Rudolph lookalikes, flowering plants get busy at the epigenetic level. At the onset of winter, plants in temperate regions, such as Arabidopsis thaliana, undergo a process called vernalization where they prep to quickly flower once spring rolls back around. As Jae Bok Heo and Sibum Sung at the University of Texas at Austin demonstrate in their new Science pub, vernalization in Arabidopsis involves some serious histone methylation that’s orchestrated by a string of RNA.
In Arabidopsis, vernalization involves the shutdown of a floral repressor called FLOWERING LOCUS C (FLC) by increasing levels of tri-methylated histone H3 Lys27 at that locus. This epigenetic change gets carried out by the Polycomb Repressive Complex 2 (PRC2), which includes a histone methyltransferase. PRC2’s presence at FLC increases during and after vernalization.
So what recruits PRC2 to the locus? Diving in with a RT-PCR approach, the investigators identified COLD ASSISTED INTRONIC NONCODING RNA (COLDAIR), a long, intronic, noncoding stretch of RNA as the recuiting element. COLDAIR is transcribed from the FLC intron itself, where a cryptic promoter becomes active while FLC is being repressed. The team showed that COLDAIR grabs PRC2 and directs the complex over to the FLC locus to maintain the gene’s silence.
So grab a cup of hot cocoa and check out the article at ScienceXpress, December 2010.