Abstract
FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) is a blue-light receptor whose function is related to flowering promotion under long-day conditions in Arabidopsis thaliana. However, information about the physiological role of FKF1 in day-neutral plants and even the physiological role other than photoperiodic flowering is lacking. Thus, the FKF1 homolog SlFKF1 was investigated in tomato, a day-neutral plant and a useful model for plants with fleshy fruit. It was confirmed that SlFKF1 belongs to the FKF1 group by phylogenetic tree analysis. The high sequence identity with A. thaliana FKF1, the conserved amino acids essential for function, and the similarity in the diurnal change in expression suggested that SlFKF1 may have similar functions to A. thaliana FKF1. CONSTANS (CO) is a transcription factor regulated by FKF1 and is responsible for the transcription of genes downstream of CO. cis-Regulatory elements targeted by CO were found in the promoter region of SINGLE FLOWER TRUSS (SFT) and RIN, which are involved in the regulation of flowering and fruit ripening, respectively. The blue-light effects on SlFKF1 expression, flowering, and fruit lycopene concentration have been observed in this study and previous studies. It was confirmed in RNA interference lines that the low expression of SlFKF1 is associated with late flowering with increased leaflets and low lycopene concentrations. This study sheds light on the various physiological roles of FKF1 in plants.
Highlights
Cryptochrome (CRY) and phototropin are blue-light receptors in plants [1]
On the alignment based on the amino acid sequence, SlFKF1 was 75.1% identical to A. thaliana FKF1, and the amino acids essential for the function of FKF1 were conserved in SlFKF1 [15,16,32] (Figure 1A)
As a result of a phylogenetic tree analysis based on alignment, including ZTL groups having the same domain structure as FKF1 but different functions, it was deduced that SlFKF1 belongs to the FKF1 group (Figure 1B)
Summary
Cryptochrome (CRY) and phototropin are blue-light receptors in plants [1]. Even in long-day plants other than A. thaliana, flowering promotion by blue light, which is supposed to involve CRY, has been reported in Petunia and Eustoma [9,10]. There are other blue-light receptors, such as FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1), and ZEITLUPE (ZTL), whose function is reportedly related to flowering promotion under long-day conditions in A. thaliana. FKF1 interacts with GIGANTEA (GI) in a blue-light-dependent manner in A. thaliana and induces the degradation of CYCLING DOF FACTOR 1 (CDF1), which suppresses CO transcription, and its family proteins [12,13,14,15]. FKF1 stabilizes the CO protein by suppressing its degradation by CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) and SUPPRESSOR
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