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Abstract
Phalaenopsis has a zygomorphic floral structure, including three outer tepals, two lateral inner tepals and a highly modified inner median tepal called labellum or lip; however, the regulation of its organ development remains unelucidated. We generated RNA-seq reads with the Illumina platform for floral organs of the Phalaenopsis wild-type and peloric mutant with a lip-like petal. A total of 43,552 contigs were obtained after de novo assembly. We used differentially expressed gene profiling to compare the transcriptional changes in floral organs for both the wild-type and peloric mutant. Pair-wise comparison of sepals, petals and labellum between peloric mutant and its wild-type revealed 1,838, 758 and 1,147 contigs, respectively, with significant differential expression. PhAGL6a (CUFF.17763), PhAGL6b (CUFF.17763.1), PhMADS1 (CUFF.36625.1), PhMADS4 (CUFF.25909) and PhMADS5 (CUFF.39479.1) were significantly upregulated in the lip-like petal of the peloric mutant. We used real-time PCR analysis of lip-like petals, lip-like sepals and the big lip of peloric mutants to confirm the five genes’ expression patterns. PhAGL6a, PhAGL6b and PhMADS4 were strongly expressed in the labellum and significantly upregulated in lip-like petals and lip-like sepals of peloric-mutant flowers. In addition, PhAGL6b was significantly downregulated in the labellum of the big lip mutant, with no change in expression of PhAGL6a. We provide a comprehensive transcript profile and functional analysis of Phalaenopsis floral organs. PhAGL6a PhAGL6b, and PhMADS4 might play crucial roles in the development of the labellum in Phalaenopsis. Our study provides new insights into how the orchid labellum differs and why the petal or sepal converts to a labellum in Phalaenopsis floral mutants.
Highlights
Orchids (Orchidaceae) represent one of the largest families of flowering plants, with more than 25,000 species [1]
To reveal putative roles in labellum development of Phalaenopsis flower, we evaluated the association of the expression of five transcription factors (TFs) (PhMADS1, PhMADS4, PhMADS5, PhAGL6a and PhAGL6b) in the floral organs and different floral morphologic features of Phalaenopsis orchid mutants from our collection (Fig 5; Fig E in S1 File)
We examined global transcriptome landscapes from six floral organ tissues of the wild-type and peloric-mutant Phalaenopsis orchid and identified preferentially expressed genes within and among floral organ developmental tissues
Summary
Orchids (Orchidaceae) represent one of the largest families of flowering plants, with more than 25,000 species [1]. Somaclonal variation, characterized by phenotypic changes of genetic or epigenetic origin [4], has been extensively studied in several plants. Such variation includes morphological traits such as flower color and morphologic features, leaf morphologic features and color, plant height, resistance to disease, improved quality and higher yield [5]. The labellum-like petal of the peloric mutant of Phalaenopsis is more common than in other somaclonal variants. The orchid peloric mutant is valuable for investigating flower development at both morphological and molecular levels
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