Ezequiel Nazer and Alberto R. Kornblihtt; PNAS December 28, 2021 118 (52) e2120124118

Figure 1: Molecular bases of the control of the FLC gene expression by AGO1, COOLAIR RNA processing, and chromatin state. (Top) Expression of FLC, promoted by the THO/TREX complex, prevents flowering. (Bottom) AGO1 and FCA collaborate to promote repression of FLC expression through COOLAIR shortening and the replacement of permissive (H3K4me1) by repressive (H3K27me3) histone marks, which triggers flowering. Pol II, RNA polymerase II.

In PNAS, Xu et al. (1) report that a member of the Argonaute family of proteins, Argonaute 1 (AGO1), is an essential actor in the gene control of flowering. In Arabidopsis thaliana, flowering is inhibited when the floral repressor gene FLOWERING LOCUS C (FLC) is expressed. Therefore, repression of FLC expression is necessary to trigger flowering. Repressors of FLC expression include evolutionary conserved RNA binding proteins such as FCA, FPA, and FLK as well as factors that regulate messenger RNA (mRNA) processing and chromatin structure. A gene can be defined as a stretch of DNA sequence able to be transcribed, rendering either an RNA with a function itself or an mRNA that is translated by the ribosomes into a protein as a final product. Transcription of genes begins at sequences known as promoters, usually located at one of the ends of a gene known as the 5′ end. Promoters are usually not transcribed, but they dictate the beginning of transcription by the enzyme RNA polymerase II at a nucleotide known as the +1 or transcription start site. At the opposite end of the gene, known as its 3′ end, a complex multimolecular assembly determines the end of the RNA transcript. Even though genes are made of double-stranded DNA, only one of the strands serves as a template for the RNA; the other DNA strand is generally not transcribed, but, in some cases, it may be transcribed from a promoter located at the 3′ end of the gene so the RNA polymerase II travels in the opposite direction, giving rise to an antisense RNA. The FLC gene follows this model, with FLC mRNA being produced from the 5′ promoter, and a set of antisense long noncoding RNAs called COOLAIR being produced from the 3′ promoter.

See more: https://www.pnas.org/content/118/52/e2120124118