LWD1 and LWD2 in Arabidopsis photoperiod regulation

Transcriptome analysis has revealed a light-regulated WD (tryptophan and aspartate)-containing protein, LWD1. LWD1 and LWD2 share greater than 90% amino acid sequence homology. The lack of phenotype changes in the lwd1 or lwd2 single mutant implies that the proteins function redundantly. The lwd1lwd2 double mutant, however, has an early flowering phenotype under both long-day (LD) and short-day (SD) conditions. Functional complementation experiment revealed that LWDs are indeed responsible for the defect in photoperiod sensing in lwd1lwd2 double mutant plants. The expression of LWD1 exhibits a diurnal pattern and peaks before dawn. The period length of oscillator (CCA1, LHY, TOC1 and ELF4) and output (CCR2 and CAB2) genes in the lwd1lwd2 double mutant is significantly shorter than that in wild-type Arabidopsis under free running condition. Under entrainment conditions, the expression phase of oscillator (CCA1, LHY, TOC1 and ELF4) and output (GI, FKF1, CDF1, CO and FT) genes shifts ~3 hr forward in the lwd1lwd2 double mutant. Our data indicated that the early flowering phenotype in lwd1lwd2 plants is contributed by the significant phase shift of CO and, therefore, an increased expression of FT before dusk under SD conditions. Our data imply that LWD1/LWD2 proteins function in close proximity to the circadian oscillators for the regulation of photoperiod sensing.

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Wu JF, Wang Y, Wu SH