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Virus-induced gene silencing unravels multiple transcription factors involved in floral growth and development in Phalaenopsis orchids.

ABSTRACT: Orchidaceae, one of the largest angiosperm families, has significant commercial value. Isolation of genes involved in orchid floral development and morphogenesis, scent production, and colouration will advance knowledge of orchid flower formation and facilitate breeding new varieties to increase the commercial value. With high-throughput virus-induced gene silencing (VIGS), this study identified five transcription factors involved in various aspects of flower morphogenesis in the orchid Phalaenopsis equestris. These genes are PeMADS1, PeMADS7, PeHB, PebHLH, and PeZIP. Silencing PeMADS1 and PebHLH resulted in reduced flower size together with a pelaloid column containing petal-like epidermal cells and alterations of epidermal cell arrangement in lip lateral lobes, respectively. Silencing PeMADS7, PeHB, and PeZIP alone resulted in abortion of the first three fully developed flower buds of an inflorescence, which indicates the roles of the genes in late flower development. Furthermore, double silencing PeMADS1 and PeMADS6, C- and B-class MADS-box genes, respectively, produced a combinatorial phenotype with two genes cloned in separate vectors. Both PeMADS1 and PeMADS6 are required to ensure the normal development of the lip and column as well as the cuticle formation on the floral epidermal cell surface. Thus, VIGS allows for unravelling the interaction between two classes of MADS transcription factors for dictating orchid floral morphogenesis.

SUBMITTER: Hsieh MH

PROVIDER: S-EPMC3745740 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Virus-induced gene silencing unravels multiple transcription factors involved in floral growth and development in Phalaenopsis orchids.

Hsieh Ming-Hsien MH Pan Zhao-Jun ZJ Lai Pei-Han PH Lu Hsiang-Chia HC Yeh Hsin-Hung HH Hsu Chia-Chi CC Wu Wan-Lin WL Chung Mei-Chu MC Wang Shyh-Shyan SS Chen Wen-Huei WH Chen Hong-Hwa HH

Journal of experimental botany 20130901 12

Orchidaceae, one of the largest angiosperm families, has significant commercial value. Isolation of genes involved in orchid floral development and morphogenesis, scent production, and colouration will advance knowledge of orchid flower formation and facilitate breeding new varieties to increase the commercial value. With high-throughput virus-induced gene silencing (VIGS), this study identified five transcription factors involved in various aspects of flower morphogenesis in the orchid Phalaeno ...[more]

PMID: 23956416

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Project description:BACKGROUND:Phalaenopsis represents an important cash crop worldwide. Abundant flower colors observed in Phalaenopsis orchids range from red-purple, purple, purple-violet, violet, and violet-blue. However, violet-blue orchids are less bred than are those of other colors. Anthocyanin, vacuolar pH and metal ions are three major factors influencing flower color. This study aimed to identify the factors causing the violet-blue color in Phalaenopsis flowers and to analyze whether delphinidin accumulation and blue pigmentation formation can be achieved by transient overexpression of heterologous F3'5'H in Phalaenopsis. RESULTS:Cyanidin-based anthocyanin was highly accumulated in Phalaenopsis flowers with red-purple, purple, purple-violet, and violet to violet-blue color, but no true-blue color and no delphinidin was detected. Concomitantly, the expression of PeF3'H (Phalaenopsis equestrsis) was high, but that of PhF3'5'H (Phalaenopsis hybrid) was low or absent in various-colored Phalaenopsis flowers. Transient overexpression of DgF3'5'H (Delphinium grandiflorum) and PeMYB2 in a white Phalaenopsis cultivar resulted a 53.6% delphinidin accumulation and a novel blue color formation. In contrast, transient overexpression of both PhF3'5'H and PeMYB2 did not lead to delphinidin accumulation. Sequence analysis showed that the substrate recognition site 6 (SRS6) of PhF3'5'H was consistently different from DgF3'5'Hs at positions 5, 8 and 10. Prediction of molecular docking of the substrates showed a contrary binding direction of aromatic rings (B-ring) with the SRS6 domain of DgF3'5'H and PhF3'5'H. In addition, the pH values of violet-blue and purple Phalaenopsis flowers ranged from 5.33 to 5.54 and 4.77 to 5.04, respectively. Furthermore, the molar ratio of metal ions (including Al3+, Ca2+ and Fe3+) to anthocyanin in violet-blue color Phalaenopsis was 190-, 49-, and 51-fold higher, respectively, than those in purple-color Phalaenopsis. CONCLUSION:Cyanidin-based anthocyanin was detected in violet-blue color Phalaenopsis and was concomitant with a high pH value and high molar ratio of Al3+, Ca2+ and Fe3+ to anthocyanin content. Enhanced expression of delphinidin is needed to produce true-blue Phalaenopsis.

Project description:Background and aimsThe deception strategies of orchids remain poorly understood, especially in regard to the chemical compounds emitted from their flowers and their interaction with various taxonomic groups of pollinators. We investigated the phylogenetic relationships and compared the variation of floral chemical compounds between food-deceptive Dactylorhiza taxa (D. incarnata var. incarnata and D. incarnata var. ochroleuca, D. fuchsii and D. majalis) from populations in north-eastern Poland. We propose a model of the evolution of deception based on floral chemical signals in this genus.MethodsA Bayesian approach based on polymorphic plastid DNA (trnL, trnF and psbC-trnK), internal transcribed spacer (ITS) sequences and flow cytometry data was applied to confirm the taxonomic status of the studied orchids. We also identified and classified the pollinators and flower visitors in each Dactylorhiza population to the taxonomic level and compared our results with literature data. The chemical composition of pentane and diethyl ether extracts from the flowers was analysed by gas chromatography-mass spectrometry. Variation of the floral chemical components was visualized by non-metric multidimensional scaling based on Bray-Curtis dissimilarity.Key resultsThe genetic distinctiveness of D. incarnata, D. fuchsii and D. majalis was confirmed. No hybrids between them were found, but the chloroplast DNA (cpDNA), ITS haplotypes and flow cytometry showed genetic similarity between D. incarnata var. incarnata and D. incarnata var. ochroleuca. We determined that Apis mellifera (Hymenoptera) was the only shared pollinator of these taxa. Strangalia attenuata and Alosterna tabacicolor (Coleoptera) and Volucella pellucens and V. bombylans (Hymenoptera) were observed pollinating D. fuchsii. Visualization of the emission rates of the 61 floral chemical compounds detected from pentane extracts (mainly hydrocarbons and aldehydes) and the 51 from diethyl extracts (with abundant groups of benzenoids and non-aromatic acids) strongly differentiated D. incarnata, D. fuchsii and D. majalis, while those of the two varieties of D. incarnata (var. incarnata and var. ochroleuca) were almost identical.ConclusionsWhile the genetic data clearly supported the distinct lineages of D. incarnata, D. fuchsii and D. majalis, the patterns of emission of their flower chemical compounds were more complex within the series of shared compounds (alkanes and aldehydes) and taxon-specific compounds (benzenoids and esters). Their floral bouquet can influence the sexual, social and feeding behaviour of pollinators in different ways. We observed that the floral chemical compounds attracted both shared and species-specific pollinators to Dactylorhiza, confirming the multidirectional character of floral chemical signals in these food-deceptive taxa. Reduction of species-specific pollination levels in Dactylorhiza orchid taxa may promote hybridization between them.

Dataset Information

Virus-induced gene silencing unravels multiple transcription factors involved in floral growth and development in Phalaenopsis orchids.

Publications

Virus-induced gene silencing unravels multiple transcription factors involved in floral growth and development in Phalaenopsis orchids.

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