Takase T, Nishiyama Y, Tanihigashi H, Ogura Y, Miyazaki Y, Yamada Y, Kiyosue T

LOV KELCH PROTEIN2 (LKP2), ZEITLUPE (ZTL)/LOV KELCH PROTEIN1 (LKP1), and FLAVIN-BINDING KELCH REPEAT F-BOX1 (FKF1) constitute a family of Arabidopsis F-box proteins that regulate the circadian clock. Overexpression of LKP2 or ZTL causes arrhythmicity of multiple clock outputs under constant light and in constant darkness. Here, we show the significance ...

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of LKP2 and ZTL in the photoperiodic control of flowering time in Arabidopsis. In LKP2-overexpressing plants, CO and FT expression levels were downregulated under long-day conditions. LKP2 and ZTL physically interacted with FKF1, which they recruited from the nucleus into cytosolic speckles. LKP2 and ZTL inhibited the interaction of FKF1 with CYCLING DOF FACTOR 1, a ubiquitination substrate for FKF1 that is localized in the nucleus. The Kelch repeat regions of LKP2 and ZTL were sufficient for their physical interaction with FKF1 and translocation of FKF1 to the cytoplasm. Overexpression of LKP2 Kelch repeats induced late flowering under long-day conditions. lkp2 ztl double-mutant plants flowered earlier than the wild-type plants under short-day (non-inductive) conditions, and both CO and FT expression levels were upregulated in the double-mutant plants. The early flowering of lkp2 ztl depended on FKF1. LKP2, ZTL, or both affected the accumulation of FKF1 protein during the early light period. These results suggest that an important role of LKP2 and ZTL in the photoperiodic pathway is repression of flowering under non-inductive conditions, depending on FKF1.

Date: Apr. 22, 2011

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