Overexpression of lettuce TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) transcription factor genes (LsTCP13 and LsTCP17) promotes flowering time through upregulation of AtFT and AtAP1 in Arabidopsis

A family of plant-specific TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) transcription factors function in plant growth and development such as flowering time and thermomorphogenesis. To investigate the biological roles of three lettuce TCP genes homologous to Arabidopsis thaliana TCP5 (AtTCP5), TCP13 (AtTCP13), and TCP17 (AtTCP17), we first isolated LsTCP5, LsTCP13, and LsTCP17 from a lettuce cultivar. The amino acid sequences of the respective LsTCP proteins were 38–46% identical to the corresponding AtTCP proteins. LsTCP5, LsTCP13, and LsTCP17 expression were different in four tissues and were gradually decreased during vegetative growth. Our subcellular localization and yeast two hybrid analyses also showed that the three LsTCP proteins targeted in the nucleus and could interact with FLOWERING LOCUS D (FD) and PHTOCHROME INTERACTING FACTOR4 (PIF4) in lettuce. p35S::LsTCP13 and p35S::LsTCP17 Col-0 plants accelerated flowering by upregulating Arabidopsis FLOWERING LOCUS T (AtFT) and APETALA1 (AtAP1) expression, implying that LsTCP13 and LsTCP17 positively controls flowering time. Our results demonstrated that the three LsTCPs are the functional counterparts of corresponding AtTCPs, and also suggested that at least two LsTCPs may be valuable for the genetic engineering of flowering time in lettuce using genome-editing technology.