Disrupting FKF1 homodimerization increases FT transcript levels in the evening by enhancing CO stabilization

Area of Science:

• Plant Biology
• Molecular Biology
• Genetics

Background:

• The blue-light photoreceptor FKF1 (FLAVIN-BINDING, KELCH REPEAT, F-BOX 1) is essential for inducing FLOWERING LOCUS T (FT) expression under long days in Arabidopsis thaliana.
• FKF1 regulates FT, the primary florigenic signal, by forming dimers with FT regulators in the late afternoon.
• The mechanism by which FKF1 homodimer disruption impacts flowering time was previously unclear.

Purpose of the Study:

• To elucidate the role of FKF1 homodimerization in regulating FT expression and flowering time.
• To investigate how disrupting FKF1 homodimer formation affects CONSTANS (CO) stability and FT induction.
• To understand the molecular interactions involving FKF1 variants, GIGANTEA (GI), and COP1 in controlling flowering.

Main Methods:

• Utilized a variant FKF1 I160R known to disrupt homodimer formation in vitro.
• Introduced the FKF1 I160R variant into an fkf1 mutant background in Arabidopsis thaliana.
• Analyzed FT expression levels, CO protein stability, and protein-protein interactions (FKF1-FKF1, FKF1-GI, CO-COP1) under long-day conditions.

Main Results:

• The FKF1 I160R variant significantly increased FT expression under long days compared to wild-type FKF1.
• FKF1 I160R exhibited diminished FKF1 homodimerization but enhanced interaction with GI.
• FKF1 I160R stabilized CO by promoting its binding to COP1, leading to increased CO abundance in the afternoon.

Conclusions:

• FKF1 dimerization is critical for precise regulation of FT levels and flowering time.
• Attenuating FKF1 homodimerization accelerates flowering by enhancing CO stability and FT expression.
• Modulating FKF1 homodimerization and heterodimerization offers a mechanism for plants to fine-tune FT expression and adapt to light cues.