Transcriptional Regulation Of Auxin Synthase Gene TAA1 By Light And Hormone Signaling

Auxin is an important plant hormone that regulates plant development and responds to environmental stimulus.Auxin is synthesized in specific tissues and its synthesis regulation is involved in the establishment of Auxin concentration gradient.Up to now,little is known about the expression regulation mechanism of Auxin synthesis gene,only the environmental high temperature,shade,metal stress,ethylene or other hormones are reported to regulate the Auxin synthesis gene,such as YUCCA and so on.As the energy source and key signal of plant growth,the regulation principle of Auxin synthesis gene by light is still to be explored.Indolepyruvate(IPA)pathway is an important pathway for the synthesis of Auxin indoleacetic acid(IAA)in Arabidopsis thaliana.TRYPTOPHAN AMINOTRAANSFERASE OF ARABIDOPSIS 1(TAA1)catalyzes the synthesis of IPA from L-tryptophan,which is the first step of the IPA pathway.In previous studies,we found that the transcription level of TAA1 was regulated by light during de-etiolation process,and the regulation patterns in cotyledons and hypocotyls were opposite.In this paper,we further explore the molecular mechanism of this regulation.First of all,Ethylene signaling and Brassinosteroid signaling were found to positively regulate TAA1 expression in the hypocotyls by the treatment with various hormone synthesis inhibitors in the dark;Meanwhile,TAA1 transcription differences in key factor mutants of various hormone signaling pathways in the dark were analyzed by qRT-PCR,and the results show that when the Ethylene signal transcription factor EIN3,Brassinosteroid signal receptor BR11 and abscisic acid signal transcription factor ABI4 were absence,high expression of TAA1 in hypocotyls was reduced,these results suggest that TAA1 expression at hypocotyls is synergistically regulated by multiple hormone signals.In addition,ABI4 protein level increased in cotyledons but decreased in hypocotyls,and ABI4 also mediated up-regulated expression of TAA1 in cotyledons after illumination.Photomorphogenesis factor COP1 was also involved in the transcriptional regulation of TAA1.This study provides ideas for exploring the synergistic regulation of Auxin synthesis gene expression by light and hormone signal,and lays a foundation for further analyzing the molecular mechanism of TAA1 transcriptional regulation.