Functional characterization of GI and CO homologs from Eriobotrya deflexa Nakai forma koshunensis.

KEY MESSAGE: The first report of the cloning and characterization of the flowering time-regulating genes GI and CO homologs from loquat. Flowering time is critical for successful reproduction in plants. In fruit trees, it can also influence the fruit yield and quality. In the previous work, we cloned the important florigen one EdFT and two EdFDs from wild loquat (Eriobotrya deflexa Nakai forma koshunensis); however, the upstream transcription factors are still unknown. The photoperiod pathway genes GIGANTEA (GI) and CONSTANS (CO) have been reported to mainly regulate FT expression in model plants. In this work, we first cloned photoperiod pathway orthologs EdGI and EdCO from E. deflexa Nakai f. koshunensis. Phylogenetic analysis showed they are highly conserved to those from Arabidopsis. They are mainly expressed in the leaves. The EdGI and EdCO were localized in the nucleus. Their expression showed in photoperiodic regulation, while the EdCO transcripts reached the peak at different periods from that of CO in Arabidopsis. Moreover, EdCO significantly activated the EdFT promoter activity. In the transgenic Arabidopsis, downstream-flowering genes like FT and AP1 were obviously upregulated, and consequently resulted in early-flowering phenotype compared to the wild type. These data revealed that the EdGI and EdCO may play a similar role as GI and CO in Arabidopsis, and regulate flower initiation in loquat.