ReLong-day promotion of RFT1 expression
Rice is a facultative short-day plant and can finally flower
during non-inductive LD conditions. One can assume
that although Hd3aexpression is quite low during LD,
residual Hd3a activity eventually makes the plant flower.
AlthoughHd3aRNAi suppression strongly delays flowering only during SD, Hd3aRNAi plants flower quite
normally during LD [15
]. This observation indicates
the presence of another key factor promoting flowering
during non-inductive LD. Detailed analysis of flowering
mutants revealed that this factor isRICE FLOWERING
LOCUS T1(RFT1), the closest paralog of Hd3a[15
].
RFT1RNAi suppression showed a contrasting phenotype
fromHd3aRNAi.RFT1RNAi suppression had no effect
on flowering in SD conditions but impaired flowering
specifically during LD. Consistent with this observation,
RFT1expression increased during LD in leaf phloem
tissue, and RFT1 protein was shown to move from leaves
to the shoot apex by using a RFT1-GFP fusion protein.
All these observations strongly indicate that RFT1 is the
LD-specific florigen, and rice uses two florigen genes