Overexpression of BcPIF4-1 affects flowering time and hypocotyl length by regulating AtFT and AtIAA29 expression, respectively, in Arabidopsis thaliana.

PHYTOCHROME INTERACTING FACTOR4 (PIF4) plays an important role in regulating plant thermomorphogenesis. In this study, two PIF4 homologous genes, BcPIF4-1 and BcPIF4-2 (Brassica rapa subsp. CHINENSIS PIF4-1 and PIF4-2), were investigated. Amino acid sequence comparison with Arabidopsis thaliana PIF4 (AtPIF4) showed that BcPIF4-1 and BcPIF4-2 had an active phytochrome B binding (APB) motif at the N-terminus and a basic helix-loop-helix (bHLH) domain at the C-terminus. Both BcPIF4-1 and BcPIF4-2 were highly expressed in the leaves of Pak choi and showed increasing expression patterns during vernalization. Subcellular localization and yeast two-hybrid analyses also showed that the three BcPIF4-1 and BcPIF4-2 proteins were localized in the nucleus and could interact with Pak choi and Arabidopsis TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS (BcTCPs and AtTCPs). Interestingly, transgenic approaches have shown that the overexpression of only BcPIF4-1 in Col-0 and pif4-101 plants results in early flowering phenotypes by upregulating the expression of Arabidopsis FLOWERING LOCUS T (AtFT). An important BcPIF4-1 motif that directly binds to the AtFT promoter is also suggested in this study. Furthermore, the overexpression of BcPIF4-1 in Col-0 and pif4-101 plants affected hypocotyl length by increasing the expression levels of Arabidopsis INDOLE-3-ACETIC ACID INDUCIBLE 29 (AtIAA29). Our results indicate that BcPIF4-1 isolated from Pak choi is a functional equivalent of AtPIF4 in terms of flowering time and hypocotyl elongation, suggesting that BcPIF4-1 is a candidate gene for developing high-temperature-insensitive Pak choi cultivars. MAIN CONCLUSION: Pak choi BcPIF4-1 controls flowering time and hypocotyl length by affecting AtFT and AtIAA29 expression, respectively in Arabidopsis.