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J Exp Bot

Title:		PbbHLH4 regulates floral monoterpene biosynthesis in Phalaenopsis orchids
Author(s):		Chuang YC; Hung YC; Tsai WC; Chen WH; Chen HH;
Address:		"Department of Life Sciences, National Cheng Kung University, Tainan, Taiwan. Institute of Tropical Plant Sciences, National Cheng Kung University, Tainan, Taiwan. Orchid Research and Development Center, National Cheng Kung University, Tainan, Taiwan"
Journal Title:		J Exp Bot
Year:		2018
Volume:		69
Issue:		18
Page Number:		4363 - 4377
DOI:		10.1093/jxb/ery246
ISSN/ISBN:		1460-2431 (Electronic) 0022-0957 (Print) 0022-0957 (Linking)
Abstract:		"Floral scent is an important factor in attracting pollinators and repelling florivores. In Phalaenopsis bellina (Orchidaceae), the major floral scent components are monoterpenoids. Previously, we determined that expression of GERANYL DIPHOSPHATE SYNTHASE (PbGDPS) is highly correlated with monoterpene biosynthesis in Phalaenosis orchids. Here, we found that both cis- and trans-regulation were present on the GDPS promoters, with trans-regulation playing a key role. To investigate the regulation of biosynthesis of floral scent, we compared the transcriptomic data of two Phalaenopsis orchids with contrasting scent phenotypes. Eight transcription factors (TFs) that exhibited sequential elevation in abundance through floral development in P. bellina were identified, and their transcript levels were higher in the scented orchid than the scentless one. Five of these TFs transactivated several structural genes involved in monoterpene biosynthesis including PbbHLH4, PbbHLH6, PbbZIP4, PbERF1, and PbNAC1. Ectopic transient expression of each of these TFs in scentless orchids resulted in stimulation of terpenoid biosynthesis. PbbHLH4 most profoundly induced monoterpene biosynthesis, with a 950-fold increase of monoterpenoid production in the scentless orchid. In conclusion, we determined that biosynthesis of orchid floral monoterpenes was sequentially regulated, with PbbHLH4 playing a crucial role for monoterpene biosynthesis"
Keywords:		"Flowers/metabolism *Gene Expression Regulation, Plant Monoterpenes/*metabolism Odorants/analysis Orchidaceae/*genetics/metabolism Plant Proteins/*genetics/metabolism Transcription Factors/*genetics/metabolism *Transcriptome;"
Notes:		"MedlineChuang, Yu-Chen Hung, Yi-Chu Tsai, Wen-Chieh Chen, Wen-Huei Chen, Hong-Hwa eng Research Support, Non-U.S. Gov't England 2018/07/10 J Exp Bot. 2018 Aug 14; 69(18):4363-4377. doi: 10.1093/jxb/ery246"