Etiolated Arabidopsis seedlings open their cotyledons and halt rapid elongation of hypocotyl when exposed to light (de-etiolation). Major light responsive components in this process have been identified and signaling pathways revealed, yet how the organ-specific light responses are achieved remains unknown. Here we report that a developmental regulator TCP4 (TEOSINTE BRANCHED1, CYCLOIDEA, and PCF) participates in photomorphogenesis and facilitates light-induced cotyledon-opening. We demonstrate that TCP4-like transcriptional factors, which predominantly express in cotyledons of both light and dark seedlings, activate SAUR16 and SAUR50 in response to light. Light repressor PIF3 (or PIFs, phytochrome-interacting factors), which accumulates in etiolated seedlings and rapidly declines upon light exposure, inhibits TCP4 promoter-binding and prevents activation of SAUR16/50 in darkness. Our study reveals how an interplay between light responsive factors and developmental regulators leads to signal-dependent and tissue-specific regulation of gene expressions, which ultimately resulted in organ-specific light responses during de-etiolation. Overall design: Cotyledon mRNA profiles of 4-day-old dark grown Col, mTCP4#4 and mTCP4#10 seedlings were generated by deep sequencing.