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. 2022 Jan 25;12:781988. doi: 10.3389/fpls.2021.781988

FIGURE 2.

FIGURE 2

GIGANTEA plays a central role in photoperiod sensing and mediates the impact of photoperiod on stress responses. The circadian clock is an internal time-keeping mechanism involved in photoperiod sensing. The main regulatory components of the circadian clock are shown including their mutual transcription-translation feedback loops. GIGANTEA is expressed late in the afternoon and the protein improves the stability of ZEITLUPE (ZTL) upon blue light perception thereby targeting TOC1 and PRR5 for proteasomal degradation, reinforcing the entrainment of the clock. Upon blue light perception, GI interacts also with FKF1 causing the degradation of CYCLING DOF FACTOR1 (CDF1), which is a transcriptional repressor of CONSTANS (CO), encoding a central protein in photoperiod-dependent flowering. In addition, GI regulates the miR172-mediated post-transcriptional downregulation of several floral repressor genes. Besides its role in photoperiod-dependent flowering, GI has a central role in the photoperiod-dependent plant responses to drought, osmotic, cold, and oxidative stress. Dashed lines mark protein–protein interactions upon blue light perception. For more detailed information about the different pathways, please refer to section “Molecular Mechanisms Involved in the Perception of Light and the Photoperiod.” AP2, APETALA2; CCA1, CIRCADIAN CLOCK ASSOCIATED1; LHY, LATE ELONGATED HYPOCOTYL; PRR, PSEUDO-RESPONSE REGULATOR, TOC1, TIMING OF CAB EXPRESSION1; ELF3, EARLY FLOWERING3; ELF4, EARLY FLOWERING4; LUX, LUX ARRHYTHMO; FKF1, FLAVIN-BINDING KELCH REPEAT F-BOX1; TOE1, TARGET OF EAT1; TOE2, TARGET OF EAT2; SMZ, SCHLAFMÜTZE; SNZ, SCHNARCHZAPFEN.