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J Exp Bot. 2017 Nov 2;68(18):5117-5127. doi: 10.1093/jxb/erx328.

Contribution of major FLM isoforms to temperature-dependent flowering in Arabidopsis thaliana.

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Max Planck Institute for Developmental Biology, Department of Molecular Biology, Spemannstr. 35, 72076 Tübingen, Germany.
Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE-901 87 Umeå, Sweden.


FLOWERING LOCUS M (FLM), a component of the thermosensory flowering time pathway in Arabidopsis thaliana, is regulated by temperature-dependent alternative splicing (AS). The main splicing variant, FLM-β, is a well-documented floral repressor that is down-regulated in response to increasing ambient growth temperature. Two hypotheses have been formulated to explain how flowering time is modulated by AS of FLM. In the first model a second splice variant, FLM-δ, acts as a dominant negative isoform that competes with FLM-β at elevated ambient temperatures, thereby indirectly promoting flowering. Alternatively, it has been suggested that the induction of flowering at elevated temperatures is caused only by reduced FLM-β expression. To better understand the role of the two FLM splice forms, we employed CRISPR/Cas9 technology to specifically delete the exons that characterize each splice variant. Lines that produced repressive FLM-β but were incapable of producing FLM-δ were late flowering. In contrast, FLM-β knockout lines that still produced FLM-δ flowered early, but not earlier than the flm-3 loss of function mutant, as would be expected if FLM-δ had a dominant-negative effect on flowering. Our data support the role of FLM-β as a flower repressor and provide evidence that a contribution of FLM-δ to the regulation of flowering time in wild-type A. thaliana seems unlikely.


Arabidopsis thaliana; CRISPR/Cas9; FLOWERING LOCUS M (FLM); flowering time; splice isoforms; temperature-dependent alternative splicing

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