Abstract
BackgroundSterile and fertile flowers are important evolutionary developmental phenotypes in angiosperm flowers. The development of floral organs, critical in angiosperm reproduction, is regulated by microRNAs (miRNAs). However, the mechanisms underpinning the miRNA regulation of the differentiation and development of sterile and fertile flowers remain unclear.ResultsHere, based on investigations of the morphological differences between fertile and sterile flowers, we used high-throughput sequencing to characterize the miRNAs in the differentiated floral organs of Viburnum macrocephalum f. keteleeri. We identified 49 known miRNAs and 67 novel miRNAs by small RNA (sRNA) sequencing and bioinformatics analysis, and 17 of these known and novel miRNA precursors were validated by polymerase chain reaction (PCR) and Sanger sequencing. Furthermore, by comparing the sequencing results of two sRNA libraries, we found that 30 known and 39 novel miRNA sequences were differentially expressed, and 35 were upregulated and 34 downregulated in sterile compared with fertile flowers. Combined with their predicted targets, the potential roles of miRNAs in V. macrocephalum f. keteleeri flowers include involvement in floral organogenesis, cell proliferation, hormonal pathways, and stress responses. miRNA precursors and targets were further validated by quantitative real-time PCR (qRT-PCR). Specifically, miR156a-5p, miR156g, and miR156j expression levels were significantly higher in fertile flowers than in sterile flowers, while SPL genes displayed the opposite expression pattern. Considering that the targets of miR156 are predicted to be SPL genes, we propose that miR156 may be involved in the regulation of stamen development in V. macrocephalum f. keteleeri.ConclusionsWe identified miRNAs differentially expressed between fertile and sterile flowers in V. macrocephalum f. keteleeri and provided new insights into the important regulatory roles of miRNAs in the differentiation and development of fertile and sterile flowers.
Highlights
Sterile and fertile flowers are important evolutionary developmental phenotypes in angiosperm flowers
After the Early stage (ES), sterile flowers expanded rapidly; in the Middle stage (MS), the petal area of the sterile flowers increased from 325.331 mm2 to 1028.181 mm2, whereas the fertile flower petal area increased by only 14 mm2
Relative to the normal pistils of fertile flowers, the pistils in sterile flowers lacked normal embryo sacs (Fig. 2c–f ). These results indicate that sterile flowers have remarkably low fertility, with degraded stamens and pistils, whereas the stamens and pistils are normal, displaying healthy fertility, in fertile flowers of V. macrocephalum f. keteleeri
Summary
Sterile and fertile flowers are important evolutionary developmental phenotypes in angiosperm flowers. The development of floral organs, critical in angiosperm reproduction, is regulated by microRNAs (miRNAs). Sterile flowers cannot produce fruits or seeds for the generation, they play roles in improving pollination quality by attracting pollinators and reducing the reproductive costs associated with large floral displays, enhancing reproductive success [8, 9]. MADS-box transcription factors and Zinc finger family proteins are involved in male fertile and sterile development, according to floral transcriptomic analyses [12]. Some genes, such as TCP and the GRFs family, regulate floral organ size [13]
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