FRIGIDA and related proteins have a conserved central domain and family specific N- and C- terminal regions that are functionally important
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Arabidopsis accessions are either winter-annuals, which require cold winter temperatures for spring flowering, or rapid-cycling summer annuals. Typically, winter annual accessions have functional FRIGIDA (FRI) and FRIGIDA-LIKE 1 (FRL1) proteins that promote high expression of FLOWERING LOCUS C (FLC), which prevents flowering until after winter. In contrast, many rapid-cycling accessions have low FLC levels because FRI is inactive. Using biochemical, functional and bioinformatic approaches, we show that FRI and FRL1 contain a stable, central domain that is conserved across the FRI superfamily. This core domain is monomeric in solution and primarily α-helical. We analysed the ability of several FRI deletion constructs to function in Arabidopsis plants. Our findings suggest that the C-terminus, which is predicted to be disordered, is required for FRI to promote FLC expression and may mediate protein:protein interactions. The contribution of the FRI N-terminus appears to be limited, as constructs missing these residues retained significant activity when expressed at high levels. The important N- and C-terminal regions differ between members of the FRI superfamily and sequence analysis identified five FRI families with distinct expression patterns in Arabidopsis, suggesting the families have separate biological roles.
KeywordsFRIGIDA FRIGIDA-LIKE 1 FLC Flowering Vernalization Arabidopsis
Tony Gendall for ideas and helpful discussions. Our research was supported by a University of Otago Research Grant (CLD) and the Marsden Fund (RCM). REL was funded by an AGMARDT Postdoctoral Fellowship and JMR was a recipient of a Bright Futures Enterprise PhD Scholarship from the Tertiary Education Commission and Grasslanz.
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