Abstract
Tagetes erecta is an important commercial plant of Asteraceae family. The male sterile (MS) and male fertile (MF) two-type lines of T. erecta have been utilized in F1 hybrid production for many years, but no report has been made to identify the genes that specify its male sterility that is caused by homeotic conversion of floral organs. In this study, transcriptome assembly and digital gene expression profiling were performed to generate expression profiles of MS and MF plants. A cDNA library was generated from an equal mixture of RNA isolated from MS and MF flower buds (1 mm and 4 mm in diameter). Totally, 87,473,431 clean tags were obtained and assembled into 128,937 transcripts among which 65,857 unigenes were identified with an average length of 1,188 bp. About 52% of unigenes (34,176) were annotated in Nr, Nt, Pfam, KOG/COG, Swiss-Prot, KO (KEGG Ortholog database) and/or GO. Taking the above transcriptome as reference, 125 differentially expressed genes were detected in both developmental stages of MS and MF flower buds. MADS-box genes were presumed to be highly related to male sterility in T. erecta based on histological and cytological observations. Twelve MADS-box genes showed significantly different expression levels in flower buds 4 mm in diameter, whereas only one gene expressed significantly different in flower buds 1 mm in diameter between MS and MF plants. This is the first transcriptome analysis in T. erecta and will provide a valuable resource for future genomic studies, especially in flower organ development and/or differentiation.
Highlights
Plants with male sterility have been applied effectively and economically in plant breeding for pollination control, especially in Asteraceae family, which has the unique structure of terminal capitulum that contains hundreds of florets of two different types, ray florets in the periphery and disk florets in the center
Breeders are looking for the male sterile (MS) plants with defective anthers, and degenerated petals of ray and disc florets to save the expense on manual emasculation [1, 2]
Based on our observation and former reports, we focused on the differentiation process of floret organs between MS and male fertile (MF) plant, and chose flower buds 1 mm and 4 mm in diameter for transcriptome and digital gene expression (DGE) analysis
Summary
Plants with male sterility have been applied effectively and economically in plant breeding for pollination control, especially in Asteraceae family, which has the unique structure of terminal capitulum that contains hundreds of florets of two different types, ray florets in the periphery and disk florets in the center. The previous histological and cytological analysis found that, in T. erecta, the petals of the ray and disc florets of the MS plant developed into sepal-like, while the stamens were partially converted to styles [11]. It indicated that the male sterility in T. erecta is probably caused by the homeotic conversion of stamens into other floral organ structures, i.e. corresponding to the category of male organ abnormality. In Gossypium hirsutum (Malvaceae family), thousands of genes were differentially expressed at the meiosis, tetrad, and uninucleate microspore stages of anthers [26, 27] These findings provided a better understanding of the regulatory network involved in stamen, anther and pollen development. The data will provide an invaluable resource for identifying genes involved in flower development and provide insights into the molecular mechanisms of male sterility in T. erecta
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