Changes in CsFT transcript abundance at the onset of low-temperature floral induction in sweet orange

Abstract

As in arabidopsis (Arabidopsis thaliana), putative citrus (Citrus) Flowering locus T (FT) homologs are strong promoters of flowering and apparently are key components of the molecular mechanism controlling floral induction in these species. An abundance of citrus FT gene transcripts during floral induction is consistent with the role of their products as floral-promoting signals. However, specific details about how the floral induction process is initiated and sustained remain largely unknown. We report changes in transcript abundance of a FT gene (CsFT) from sweet orange (Citrus sinensis) at the onset of floral induction by low temperatures and at different times of the day. Using a combination of field and growth room experiments, we determined that the abundance of CsFT transcripts increased within 1 day after initial exposure to cool floral-inductive temperatures, and that CsFT transcript abundance was higher in the afternoon than in the morning and evening. The presence of photoperiod cycles seemed to be required to sustain the increasing CsFT transcript abundance, because exposure to floral inductive conditions under continuous light or darkness did not increase the abundance of CsFT transcripts after 3 days. Our results suggest that the regulation of CsFT expression responds rapidly (overnight) to the onset of floralinductive cool temperatures, is sensitive to changes in temperature, and requires alternation of light and dark cycles to sustain transcript accumulation during induction.