| Viburnum macrocephalum f. keteleeri have special flower shapes, which usually comprised an outer ring of eight large sterile flowers surrounding a centre of small fertile flowers. However, the research on the development and control mechanism of V. macrocephalum f. Keteleeri is still little. Here, we used the high-throughput sequencing platform combined with bioinformatics method for the transcriptomics analysis of sterile and fertile flowers of V. macrocephalum f. Keteleeri, from the level of mRNA, to generate the highly differentially expressed genes of floral organ growth; we also used cell biology and anatomical structure to observe the morphological changes of sterile and fertile flowers during floral organ growth and development. The main results were summarized as following:(1) The floral characters, anatomy of sterile and fertile flowers of V. macrocephalum f. keteleeri were studied. The difference of morphological development between the two types of flowers were analyzed at both histologic and cytologic level.(2) Total RNAs were extracted from sterile and fertile flowers of V. macrocephalum f. Keteleeri. After the quality of the RNAs were qualified, the total RNAs were used for transcriptome sequencing. Based on Illumina HiSeqTM 2500 platform, Illumina RNA sequencing generated a total of 278,909,605 raw reads. After stringent quality checks and data cleaning, we obtained 267,723,356 clean reads of high quality. Based on these clean reads, the Trinity software generated 132,788 transcripts with a mean length of 740 bp, and 105683 unigenes were achieved.(3) Unigenes annotation was performed by BLAST searching (E-value ≤10-5) against the Nr (NCBI non-redundant protein sequences), Nt (NCBI nucleotide sequences), Pfam (protein family), KOG (euKaryotic Ortholog Groups), SwissProt (A manually annotated and reviewed protein sequence database), KEGG (Kyoto Encyclopedia of Genes and Genomes) and GO (Gene Ontology) databases. A total of 38224 unigenes (36.16% of all unigenes) were annotated with a significant BLAST result in the Nr database; 26744 unigenes were annotated in Swiss-Prot database; and 13637 unigenes (12.9%) were annotated in KOG databases; and 30381 unigenes (28.74%) were annotated in GO databases. In total,105683 unigenes were annotated in the seven databases.(4) On the basis of the threshold criteria (padj<0.05),5,765 genes (5.37% of all genes) were identified as significant DEGs between the sterile and fertile flowers. Compared with fertile flowers, there were 1,908 up-regulated genes and 3,767 down-regulated genes in sterile flowers.(5) Through screening in the DEG library between sterile flowers and fertile flowers, those genes related to floral organ development were selected, including genes related to plant growth and development. Among them, genes related to flower organ size are mainly concentrated in the aspects of cell proliferation and expansion and hormone regulation. And plant fertility related genes are mainly about flower pistil and stamen abortion, including the tapetum male sterility, programmed cell death, pollen and anther development gene, embryo sac and female gametophyte development related genes, indicating the molecular mechanisms of abortion. Meanwhile, qRT-PCR results were confirmed that significantly differentially expressed genes between the sterile and fertile flowers during the same developmental period contributed to regulating different growth and development process in the two types of flowers.(6) In this study, we found that 2,072 genes were putatively identified as Transcription factors (TFs) genes and attached to 79 TF families. Among these TF families, the MYB super-family members were the most abundant, followed by AP2-EREBP family, C2H2 domain family, bHLH family. Among identified TFs, a total of 377 TFs displayed differential expression between the fertile flowers and sterile flowers, and were classified into 54 TF families. The MADS-box TFs family involed in development of the two types of flowers were specially analyzed. |
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