Identification and functional characterization of TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) transcription factor genes in Pak-choi (Brassica rapa ssp. chinensis)

TEOSINTE BRANCHED1/ CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) are a group of plant-specific genes that encode transcription factors and play essential roles in plant growth and development. Of these genes, Arabidopsis TCP5 (AtTCP5), TCP13 (AtTCP13), and TCP17 (AtTCP17) regulate flowering time, one of the important factors of plant development. Controlling flowering time of Pak-choi (Brassica rapa ssp. chinensis) is a method of improving plant growth conditions, as vegetative tissues such as leaves are not produced after floral transition. To investigate functional conservation in three Pak-choi TCP genes homologous to AtTCP5, AtTCP13, and AtTCP17 in the regulation of flowering time, we isolated BcTCP5, BcTCP13, and BcTCP17 from a Pak-choi cultivar. The deduced amino acid sequences of the selected TCP genes were 65-82% identical to the three aforementioned AtTCP proteins. The expression levels of BcTCP5, BcTCP13, and BcTCP17 were spatially different and were unaffected by vernalization treatment. The three BcTCP proteins also localized in the nucleus, and interacted with Arabidopsis FLOWERING LOCUS D (AtFD) and PHTOCHROME INTERACTING FACTOR4 (AtPIF4). Overexpression of BcTCP17 in Arabidopsis plants led to an early flowering phenotype by up-regulating endogenous Arabidopsis FOWERING LOCUS T (AtFT) and APETALA1 (AtAP1) expression, suggesting that BcTCP17 regulates flowering time in Arabidopsis. Our results indicated that the three BcTCPs isolated from Pak-choi plants are the equivalents of corresponding AtTCPs, and that BcTCP17 may be a candidate to be used in the regulation of flowering time in Pak-choi plants utilizing the clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system.