BMB Reports : eISSN 1976-670X

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Fig. 1. Possible model of the FKF1-COP1-CO regulatory module in the photoperiod-dependent induction of flowering. The blue-light receptor FKF1 is highly expressed at ZT14 – ZT16, at which time the plants are exposed to light under LD conditions (16 h light/day), but are in the dark under SD (8 h light/day) conditions. Another blue-light receptor, CRY2, is stabilized in light, but quickly destabilized in darkness. In LD conditions, the light-activated blue-light receptors FKF1 and CRY2 interact with the COP1-SPA1 complexes, forming FKF1-COP1 and CRY2-SPA1 complexes. This might inhibit the formation of the COP1-SPA1 complexes in the late afternoon, resulting in the inactivation of COP1 or the destabilization of the COP1-SPA1 complex. Inhibition of COP1-SPA1 complex formation increases CO protein stability in the late afternoon, enabling it to interact with FKF1 and induce FT transcription for floral induction. In SD conditions, both CO and FKF1 are expressed in the dark, and CRY2 is destabilized in the dark. Thus, the blue-light receptors FKF1 and CRY2 are present in their inactive forms in darkness, and cannot destabilize COP1 complex, resulting in the rapid breakdown of CO by ubiquitin-dependent proteolysis.
BMB Reports 2018;51:163~164
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