Activation of PIF4/5 by the Transcription Factor TCP4 Promotes Hypocotyl Elongation in Arabidopsis

ABSTRACT Transcription factor TEOSINTE BRANCHED1, CYCLODEA, PROLIFERATING CELL FACTORS 4 (TCP4) plays essential roles in plant development processes. The role of TCP4 in the regulation of hypocotyl growth remains a matter of debate. Our results cast doubt on the previous claims that TCP4 directly activates YUC5 expression to promote hypocotyl elongation, and clearly show that TCP4 promotes hypocotyl elongation dependent on PIF4/5.