The spliceosomal component GAMETOPHYTIC FACTOR 1 (GFA1) regulates a key photoperiodic switch

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Abstract Plants have evolved sophisticated mechanisms to perceive and interpret daytime in order to flower at an optimal time point. Here we show that the spliceosomal component GAMETOPHYTIC FACTOR 1 ( GFA1 ) constitutes a previously unrecognized key photoperiodic switch, that is essential for flowering in long days. We show that gfa1 hypomorphic ( gfa1 hyp ) plants fail to initiate flowering in long-days (LD), which correlates with ectopic activation of the short-day (SD) flowering repressor ARABIDOPSIS THALIANA CENTRORADIALIS (ATC) . Accordingly, flowering is restored upon inactivation of ATC in gfa1 hyp mutants. A novel tissue-specific in-planta splice assay and comprehensive RNAseq profiling of gfa1 hyp mutants indicate that GFA1 mediated pre-mRNA splicing is substrate specific, as previously suggested for GFA1 orthologs. Furthermore, we show that gfa1 hyp mutants accumulate nonsense transcripts of the photoreceptor components PHYB and RRC1 , suggesting inappropriate photoreceptor signaling as a potential cause for the ectopic activation of the SD characteristic profile in gfa1 hyp . In fact, known downstream targets of the phytochrome system such as RS31, SR34a, SRp30 accumulate reduced amounts of light-dependent splice isoforms. Together, our data reveal a link between spliceosome composition and long-day flowering, based on complex transcriptional readouts in response to day length.

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