Abstract
The Formosa lily (Lilium formosanum) is one of the most common horticultural species in Taiwan. To explore gene regulation involved in this species, we used transcriptome analysis to generate PH-FB (mixed floral buds) and PH-LF (mature leaves) datasets. Combination of the PH-FB and PH-LF constructed a de novo assembly of the ALL dataset, including 18,041 contigs and 23,807 unigenes by Nr, GO, COG, and KEGG databases. The differential gene expression (DGE) analysis revealed 9937 genes were upregulated while 10,383 genes were downregulated in the developing floral buds compared to mature leaves. Seven putative genes (LFMADS1 to 7) encoding floral organ identity proteins were selected for further analysis. LFMADS1-6 genes were specifically expressed in the floral organ, while LFMADS7 in the floral buds and mature leaves. Phylogenetic analysis revealed that LFMADS1-3 is classified into B-class, LFMADS4 into C-class, LFMADS5 into D-class, and LFMADS6-7 into E-class, respectively. LFMADS-GFP fusion proteins appeared to localize in the nucleus, supporting their roles as transcription factors (TFs). Overexpression of the LFMADS2, LFMADS4, and LFMADS6 genes in Arabidopsis resulted in early flowering and floral defect, however, only early flowering in transgenic tobacco was observed. Highly expressed floral integrator genes, including AtFT, AtLFY, and AtFUL in transgenic Arabidopsis and NtFUL and NtSOC1 in transgenic tobacco, resulted in early flowering phenotype through qRT-PCR analysis. Yeast two-hybrid analysis suggested that LFMADSs may form higher order complexes with the B-, C-, D, and/or E-class proteins to determine the floral organ identity. Furthermore, E-class LFMADS proteins may function as a glue to mediate and strengthen the protein-protein interactions. Therefore, our de novo datasets would provide information for investigating other differentially expressed candidate transcripts. In addition, functional conservation of LFMADSs appears to be vital in floral transition and floral organ identity.
Highlights
Flowering functions as a switch from vegetative to reproductive growth in angiosperms, through which shoot apical meristems turn into floral meristems and develop as floral organs [1,2]
All high-quality reads were assembled de novo by using the Trinity program, producing 41,848 unigenes in ALL transcriptome dataset which was the combined results of the PH-FB and PH-LF transcriptome datasets
Our results revealed that the expression patterns of these LFMADS1-7 genes in 2-cm floral organs or mature leaves correlate well with the expression profiles from our differential gene expression (DGE) analysis, indicating the reliability of our assays
Summary
Flowering functions as a switch from vegetative to reproductive growth in angiosperms, through which shoot apical meristems turn into floral meristems and develop as floral organs [1,2]. The MADS (MCM1/AGAMOUS/DEFICIENS/SRF)-box transcription factor (TF) family genes were shown earlier to play crucial roles in controlling plant and animal development [12]. These TFs have been classified into two types (type I and type II) based on sequence relationships and structural features [13]. In the four-whorled flower of Arabidopsis, type II MADS box genes (MIKC-type) work together to specify the identity of floral organs [14,15]. In Arabidopsis, 107 MADS-box genes have been reported previously, including 39 of the MIKC-type [18], whereas 75 genes have been annotated in rice, of which 38 are MIKC-type [19]. The potential functional role of MADS-box TFs in the regulation of flower formation is still not clear
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