HD-ZIP I Transcription Factor ( PtHB13 ) Negatively Regulates Citrus Flowering through Binding to FLOWERING LOCUS C Promoter

For floral induction in adult citrus, low temperature is one of the most important environmental factors. ( ) plays a very important role in low-temperature-induced flowering by repressed expression under exposure to prolonged low-temperature conditions. However, little is known about the regulation mechanism in perennial woody plants such as citrus. In this study, the functions of citrus homolog ( ) were investigated by ectopic expression in . Transcription factor of homeodomain leucine zipper I (HD-ZIP I) as an upstream regulator of was identified by yeast one-hybrid screen to regulate its transcription. The HD-ZIP I transcription factor was highly homologous to and thus was named . Ectopically expressed inhibited flowering in transgenic . Furthermore, the expression of and showed a seasonal change during the floral induction period and was also affected by low temperature. Thus, we propose that binds to promoter to regulate its activity during the citrus floral induction process.