Abstract
<em>Phalaenopsis</em> is one of the world’s most popular and important epiphytic monopodial orchids. The extraordinary floral diversity of <em>Phalaenopsis</em> is a reflection of its evolutionary success. As a consequence of this diversity, and of the complexity of flower color development in <em>Phalaenopsis</em>, this species is a valuable research material for developmental biology studies. Nevertheless, research on the molecular mechanisms underlying flower color and floral organ formation in <em>Phalaenopsis</em> is still in the early phases. In this study, we generated large amounts of data from <em>Phalaenopsis</em> flowers by combining Illumina sequencing with differentially expressed gene (DEG) analysis. We obtained 37 723 and 34 020 unigenes from petals and labella, respectively. A total of 2736 DEGs were identified, and the functions of many DEGs were annotated by BLAST-searching against several public databases. We mapped 837 up-regulated DEGs (432 from petals and 405 from labella) to 102 Kyoto Encyclopedia of Genes and Genomes pathways. Almost all pathways were represented in both petals (102 pathways) and labella (99 pathways). DEGs involved in energy metabolism were significantly differentially distributed between labella and petals, and various DEGs related to flower color and floral differentiation were found in the two organs. Interestingly, we also identified genes encoding several key enzymes involved in carotenoid synthesis. These genes were differentially expressed between petals and labella, suggesting that carotenoids may influence <em>Phalaenopsis</em> flower color. We thus conclude that a combination of anthocyanins and/or carotenoids determine flower color formation in <em>Phalaenopsis</em>. These results broaden our understanding of the mechanisms controlling flower color and floral organ differentiation in <em>Phalaenopsis</em> and other orchids.
Highlights
Phalaenopsis amabilis, an epiphytic monopodial orchid, is an important ornamental species with a huge global market, especially in western countries
37 723 unigenes were obtained from the petals, with a final unigene N50 length of 1 125 bp and a total length of 26 656 163 nt; 34 020 unigenes were generated from the labella data, with a final unigene N50 length of 1398 bp and a total length of 27 636 110 nt
These unigenes were organized into a transcriptome database for the identification of putative genes related to flower color and floral differentiation
Summary
Phalaenopsis amabilis, an epiphytic monopodial orchid, is an important ornamental species with a huge global market, especially in western countries. Ornamental quality in Phalaenopsis is influenced by many factors, including flower color, fragrance and shape, cut-flower longevity, flowering control, and abiotic stress tolerance [1]. Phalaenopsis flowers are zygomorphic and include three outer tepals (T1–T3, known as sepals) in the first whorl, two lateral inner tepals (t1 and t2, the petals), and a median inner tepal (t3, the lip or labella) [2,3]. Orchid PI/GLO-like genes, found to be present in the AP3/ DEF-like gene copies, are necessary for current floral tissue development [4]. Despite this knowledge, the regulatory network controlling orchid floral development remains unclear
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