RNA Splicing of FLC Modulates the Transition to Flowering

Abstract

Flowering is a critical stage of plant development and is closely correlated with seed production and crop yield. Flowering transition is regulated by complex genetic networks in response to endogenous and environmental signals. FLOWERING LOCUS C (FLC) is a central repressor in the flowering transition of Arabidopsis thaliana. The regulation of FLC expression is well studied at transcriptional and post-transcriptional levels. A subset of antisense transcripts from FLC locus, collectively termed cold-induced long antisense intragenic RNAs (COOLAIR), repress FLC expression under cold exposure. Recent studies have provided important insights into the alternative splicing of COOLAIR and FLC sense transcripts in response to developmental and environmental cues. Herein, at the 20th anniversary of FLC functional identification, we summarise new research advances in the alternative splicing of FLC sense and antisense transcripts that regulates flowering.

Keywords: COOLAIR; FLOWERING LOCUS C; alternative splicing; flowering transition; splicing factor; vernalization.

Figure 1

Splicing patterns of FLC sense and antisense transcripts, and AS of FLC antisense transcripts regulating FLC expression. (A) Schematic diagram of the splicing patterns of FLC sense and antisense transcripts at FLC locus in Arabidopsis. Black rectangles, gray dash lines and boxes indicate exons, introns and non-translated regions of FLC RNAs, respectively. Gray and black lines represent the genes and promoter regions of FLC and COOLAIR loci, respectively. (B) AS variants of COOLAIR transcripts effect FLC expression. Nascent COOLAIR RNAs are physically associated with the FLC locus to regulate the switching of chromatin states (Csorba et al., 2014; Li et al., 2015; Rosa et al., 2016). Two classes of COOLAIR transcripts bind to FCA and recruit PRC2 complex to FLC locus (Tian et al., 2019). The class I variants with proximal polyadenylation and the proximal–distal ratio of COOLAIR transcripts effect the histone methylation of H3K4me2, H3K36me3 and H3K27me3 (Marquardt et al., 2014; Berry and Dean, 2015; Xiao et al., 2015; Rosa et al., 2016). The class II COOLAIR transcripts with distal polyadenylation influence the degree of capping of the FLC nascent transcripts (Li et al., 2015).