Class I TCP transcription factors target the gibberellin biosynthesis gene GA20ox1 and the growth promoting genes HBI1 and PRE6 during thermomorphogenic growth in Arabidopsis

Abstract

Plants respond to a rise in ambient temperature by increasing the growth of petioles andhypocotyls. In this work, we show that Arabidopsis thaliana class I TEOSINTEBRANCHED 1, CYCLOIDEA, PCF (TCP) transcription factors TCP14 and TCP15 arerequired for optimal petiole and hypocotyl elongation under high ambient temperature.These TCPs influence the levels of the DELLA protein RGA and the expression ofgrowth-related genes which are induced in response to an increase in temperature.However, the class I TCPs are not required for the induction of the auxin biosynthesisgene YUCCA8 or for auxin-dependent gene expression responses. TCP15 directlytargets the gibberellin biosynthesis gene GA20ox1 and the growth regulatory genesHBI1 and PRE6. Several of the genes regulated by TCP15 are also targets of the growthregulator PIF4 and show an enrichment of PIF4 and TCP binding motifs in theirpromoters. PIF4 binding to GA20ox1 and HBI1 is enhanced in the presence of the TCPs,indicating that TCP14 and TCP15 directly participate in the induction of genes involvedin gibberellin biosynthesis and cell expansion by high temperature functionallyinteracting with PIF4. In addition, overexpression of HBI1 rescues the growth defects oftcp14 tcp15 double mutants, suggesting that this gene is a major outcome of regulationby both class I TCPs during thermomorphogenesis.