OsLHY regulates photoperiodic flowering through the unique pathways
under long-day conditions in rice (Oryza sativa L.)
Abstract
Flowering time (or heading date in crops) is a critical agronomic trait
for rice reproduction and adaptation. The circadian clock is an
endogenous oscillator that is involved in controlling photoperiodic
flowering. The rice LATE ELONGATED HYPOCOTYL (OsLHY), the core
oscillator component of circadian clock, is a homolog of the LHY/CCA1 in
Arabidopsis. Here we showed that CRISPR/Cas9-engineered mutations in
OsLHY caused late flowering in rice only under long-day (LD) conditions.
In the oslhy mutant, the diurnal expression of circadian clock-related
genes was seriously affected under both LD and short-day (SD)
conditions. Furthermore, the expression of the flowering activators
Ehd1, Hd3a and RFT1 was down-regulated and flowering repressors Hd1 and
Ghd7 was up-regulated in the oslhy mutant under LD conditions. While the
transcripts of flowering-related genes were not dramatically influenced
under SD conditions. Dual-luciferase assays showed that OsLHY repressed
the transcription of OsGI, Hd1, Ghd7, Hd3a, RFT1 and OsELF3, and
activated the transcription of Ehd1. Moreover, the yeast one hybrid
assay confirmed that OsLHY directly repressed OsGI, RFT1 and OsELF3 by
binding to their promoters, which is consistent with that in
Arabidopsis. These results suggested that the OsLHY can promote rice
flowering mainly through regulating Hd1 and Ehd1 under LD conditions.