Diurnal regulation of the floral scent emission by light and circadian rhythm in the Phalaenopsis orchids

Abstract

Background Phalaenopsis bellina and its closely related species, P. violacea, emit linalool, geraniol and their derivatives as the predominant monoterpenes at the full-bloom stages. Geranyl diphosphate synthase (PbGDPS) is the key enzyme that converts precursors for monoterpene biosynthesis. Besides the monoterpenes being synthesized in concert with floral development stages, we noticed that the scent emission of P. bellina and P. violacea was detected mainly in the daytime.ResultsThe monoterpenes of P. violacea flowers displayed a diurnal emission pattern, which was regulated by an internal oscillator in the treatment of constant light. In contrast, constant dark diminished the scent emission levels, indicating that light also affects monoterpene emission in P. violacea. Further treating P. violacea with various light wavelengths showed that the monoterpene emission was greatest in white light condition. Other Phalaenopsis hybrids, including P. I-Hsin Venus ‘KHM2212’ and P. Meidarland Bellina Age ‘LM128’, responded differently to various light wavelengths but most of them still showed the highest scent emission under the whole spectra of light. A great number of light-responsive, HY5-interacting, and circadian-responsive elements was enriched on the promoters of both structural genes and transcription factors for monoterpene biosynthesis. Furthermore, several putative genes encoding components involved in light and circadian signaling pathways were also identified in the transcriptome of P. bellina flowers at consecutive stages (from the anthesis day to day 7 post anthesis).ConclusionsTaken together, both circadian clock and light factors had positive effects on orchid floral scent emission, and the regulation resided on the control of both structural genes and transcription factors for monoterpene biosynthesis.

PbbHLH4 regulates floral monoterpene biosynthesis in Phalaenopsis orchids

“…PbGDPS shows flower-specific expression, and its highest expression is concurrent with maximal emissions of monoterpenoids on day 5 post-anthesis (D+5), which suggests a crucial role of PbGDPS in floral scent production in P. bellina ( Hsiao et al , 2008 ). Recently, we found that the emission of monoterpenes is under the control of light and a circadian rhythm in Phalaenopsis orchids ( Chuang et al , 2017 ).…”

Functional Characterization of a Dendrobium officinale Geraniol Synthase DoGES1 Involved in Floral Scent Formation

“…In constant light (500 μmol·m −2 s −1 ), P. violacea emitted mostly monoterpenes whose levels decreased in constant darkness. PbNAC1, which regulates the synthesis of monoterpenes, interacts with long hypocotyl 5 (HY5), which is a positive transcription factor involved in the responsiveness of plants to light [ 5 , 39 ]. DoGES1 demonstrated fluctuations throughout the day, increasing at 8:00, then decreasing from 11:00 to 17:00, peaking at 11:00 ( Figure 7 ), corresponding to the increase and then decrease in geraniol content at the same harvest time points, with the highest value observed at 14:00, suggesting that the emission of monoterpenes may have a diurnal rhythm in D. officinale petals.…”

A Dual Repeat Cis-Element Determines Expression of GERANYL DIPHOSPHATE SYNTHASE for Monoterpene Production in Phalaenopsis Orchids

“…These individual plants were collected from various orchid nurseries across Taiwan (details in Supplementary Table 1 ). Both P. I-Hsin Venus and P. Meidarland Bellina Age are commercial scented cultivars with monoterpenes as their major scent compounds ( Chuang et al, 2017 ), whose ancestries contain multiple scent species as the following: P. I-Hsin Venus - P. amboinensis (25%), P. equestris (25%), P. venosa (18.75%), P. violacea (15.63%), P. lueddemanniana (3.13%); P. Meidarland Bellina Age - P. bellina (50%), P. violacea (24.22%), P. venosa (15.63%), P. amboinensis (3.91%), P. lueddemanniana (3.13%) via ORCHIDEYA.CA 1 . All the plant materials were grown in the greenhouse at National Cheng Kung University (NCKU) under natural light and surrounding temperature from 27 to 30°C in spring and summer with 75–85% humidity.…”

“…Analysis of the floral VOCs of 12 Phalaenopsis orchids was carried out according to the previous studies ( Hsiao et al, 2006 ; Chuang et al, 2017 ). The VOCs were collected during the most emitted scent period (from 10:00 to 16:00) by using solid phase extraction system (DSC-Si and DCS-18, Supelco, United States) as described ( Chuang et al, 2017 ), and the compounds were then identified by using gas chromatography/high-resolution mass spectrometry (GC/HRMS) at the NCKU Instrument Center ( Hsiao et al, 2006 ). To assess the amounts of each compound, 1 μg of ethyl myristate was recruited as the internal standard (Fluka, Honeywell, United States).…”

“…Standard PCRs were applied to amplify the N-terminal region of GDPS (∼400-bp) with the primer designed based on PbGDPS genomic sequence (all the primers used here and thereafter were listed in Supplementary Table 2 ) since PbGDPS is an intronless gene ( Hsiao et al, 2008 ). The 1-kb upstream promoter fragments of GDPS were also isolated from the 12 Phalaenopsis orchids using the designed primers based on the genomic DNA of P. bellina ( Chuang et al, 2017 ). The dual repeat region was then amplified and cloned with ZeroBack Fast Ligation Kit (TIANGEN, China).…”