Correct option is D
Explanation-
A. FLC (FLOWERING LOCUS C) → (iv) A strong repressor of flowering
FLC encodes a MADS-box transcription factor that represses flowering by directly inhibiting the expression of key flowering genes, such as FT and SOC1. In winter-annual accessions of Arabidopsis, FLC levels are high in young plants, preventing premature flowering. After exposure to vernalization (cold), FLC is silenced, allowing flowering to proceed in spring.
B. FD (FLOWERING LOCUS D) → (iii) Regulate target genes that mediate the reprogramming of meristem to produce flowers
FD is a transcription factor (a bZIP protein) that is expressed in the shoot apical meristem. FD partners with FT (which arrives from leaves via phloem) to form a protein complex. This complex activates target genes like APETALA1 (AP1), promoting the floral identity in the shoot apex.
C. FT (FLOWERING LOCUS T) → (ii) A mobile signal that induces flowering
FT is often referred to as “florigen”, the flowering hormone. FT is produced in leaves in response to favorable photoperiods (like long days). It then travels through the phloem to the shoot apical meristem, where it interacts with FD to initiate flowering.
D. FRI (FRIGIDA) → (i) An activator of FLC
FRI functions upstream of FLC. It activates transcription of FLC. In Arabidopsis, the FRI-FLC pathway acts as a brake on flowering. In ecotypes with a functional FRI allele, FLC levels remain high, keeping the plant from flowering until vernalization occurs.
