4.1 OsLHY has essential effect on the circadian clock
As one of the central clock oscillator components, loss-of-function ofOsLHY obviously affected the rhythmic expression pattern of
circadian clock-related genes. In Arabidopsis , LHY andCCA1 defective mutants showed shortened circadian periods (Green
& Tobin, 1999; Mizoguchi et al., 2002; Niwa et al., 2007). In theoslhy mutant, the expression peaks of OsPRR73 ,OsPRR37 , OsPRR95 , OsPRR59 , OsPRR1 andOsGI were shifted early (Figure 3), suggested that OsLHYdefective mutants could also result in shortened circadian periods.HY and CCA1 can inhibit the transcription of almost all
circadian clock-related genes in the morning (Nagel & Kay, 2012;
Sanchez & Kay, 2016). The expression of OsPRR73 andOsPRR37 was significantly reduced under LD conditions, but
increased under SD conditions in oslhy mutants. WhileOsPRR95 , OsPRR59 , OsPRR1 , OsGI andOsELF3 was increased in oslhy mutants under LD conditions
(Figure 3), which indicated that OsLHY may suppress these genes in early
time of the daytime. The expression of OsPRR1 was increased inoslhy mutants (Figure 3K and 3L), because OsLHY (orOsCCA1 ) could repress its expression by directly binding to its
promoter (Wang et al., 2020). In addition, OsLHY was
highly expressed in the osprr1 mutant (Wang et al., 2020), which
may confirm the speculation that OsLHY and OsPRR1 are
components of the central negative feedback loop in rice (Yang et al.,
2013). Overexpression of OsPRR37 suppressed the expression ofOsLHY under LD conditions (Liu et al., 2018), indicated that
reciprocally regulation between OsLHY and OsPRR37 is
complicated. In Arabidopsis, CCA1 suppresses GI and ELF3 by
interacting directly with their promoters, which add additional
connections between the circadian clock and the flowering pathways (Lu
et al., 2012). The expression of OsGI was increased at some early
daytime points (Figure 3M and 3N), and the tobacco transient expression
and Y1H showed that OsLHY can directly repress the transcription ofOsGI and OsELF3 (Figure 5A, Supplemental Figure 4 and
Figure 6). These data revealed that the additional connections among
circadian clock and the flowering pathways are conserved between rice
and Arabidopsis .