HEMERA Couples the Proteolysis and Transcriptional Activity of PHYTOCHROME INTERACTING FACTORs in Arabidopsis Photomorphogenesis

Phytochromes (phys) are red and far-red photoreceptors that control plant development and growth by promoting the proteolysis of a family of antagonistically acting basic helix-loop-helix transcription factors, the PHYTOCHROME-INTERACTING FACTORs (PIFs). We have previously shown that the degradation...

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Published in:	The Plant cell Vol. 27; no. 5; pp. 1409 - 1427
Main Authors:	Qiu, Yongjian, Li, Meina, Pasoreck, Elise K., Long, Lingyun, Shi, Yiting, Galvão, Rafaelo M., Chou, Conrad L., Wang, He, Sun, Amanda Y., Zhang, Yiyin C., Jiang, Anna, Chen, Meng
Format:	Journal Article
Language:	English
Published:	United States American Society of Plant Biologists 01-05-2015
Subjects:	Amino Acid Motifs Arabidopsis Arabidopsis - genetics Arabidopsis - growth & development Arabidopsis - metabolism Arabidopsis Proteins - genetics Arabidopsis Proteins - metabolism Basic Helix-Loop-Helix Transcription Factors - genetics Basic Helix-Loop-Helix Transcription Factors - metabolism Datasets Gene Expression Profiling Gene expression regulation Gene Expression Regulation, Plant Genes Hypocotyl - genetics Hypocotyl - growth & development Hypocotyl - metabolism Hypocotyls Microarray Analysis Mutation Phytochrome - genetics Phytochrome - metabolism Plant cells Proteins Proteolysis Recombinant Fusion Proteins Seedlings Transactivation Transcription Factors - genetics Transcription Factors - metabolism Transcriptional Activation Two-Hybrid System Techniques Yeasts
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Summary:	Phytochromes (phys) are red and far-red photoreceptors that control plant development and growth by promoting the proteolysis of a family of antagonistically acting basic helix-loop-helix transcription factors, the PHYTOCHROME-INTERACTING FACTORs (PIFs). We have previously shown that the degradation of PIF1 and PIF3 requires HEMERA (HMR). However, the biochemical function of HMR and the mechanism by which it mediates PIF degradation remain unclear. Here, we provide genetic evidence that HMR acts upstream of PIFs in regulating hypocotyl growth. Surprisingly, genomewide analysis of HMR- and PIF-dependent genes reveals that HMR is also required for the transactivation of a subset of PIF direct-target genes. We show that HMR interacts with all PIFs. The HMR-PIF interaction is mediated mainly by HMR’s N-terminal half and PIFs’ conserved active-phytochrome B binding motif. In addition, HMR possesses an acidic nine-aminoacid transcriptional activation domain (9aaTAD) and a loss-of-function mutation in this 9aaTAD impairs the expression of PIF target genes and the destruction of PIF1 and PIF3. Together, these in vivo results support a regulatory mechanism for PIFs in which HMR is a transcriptional coactivator binding directly to PIFs and the 9aaTAD of HMR couples the degradation of PIF1 and PIF3 with the transactivation of PIF target genes.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Meng Chen (dr.mengchen@gmail.com). These authors contributed equally to this work. www.plantcell.org/cgi/doi/10.1105/tpc.114.136093
ISSN:	1040-4651 1532-298X
DOI:	10.1105/tpc.114.136093