Novel and conserved microRNAs in soybean floral whorls

MicroRNAs (miRNAs) correspond to a class of endogenous small non-coding RNAs (19-24 nt) that regulates the gene expression, through mRNA target cleavage or translation inhibition. In plants, miRNAs have been shown to play pivotal roles in a wide variety of metabolic and biological processes like plant growth, development, and response to biotic and abiotic stress. Soybean is one of the most important crops worldwide, due to the production of oil and its high protein content. The reproductive phase is considered the most important for soybean yield, which is mainly intended to produce the grains. The identification of miRNAs is not yet saturated in soybean, and there are no studies linking them to the different floral organs. In this study, three different mature soybean floral whorls were used in the construction of sRNA libraries. The sequencing of petal, carpel and stamen libraries generated a total of 10,165,661 sequences. Subsequent analyses identified 200 miRNAs sequences, among which, 41 were novel miRNAs, 80 were conserved soybean miRNAs, 31 were new antisense conserved soybean miRNAs and 46 were soybean miRNAs isoforms. We also found a new miRNA conserved in other plant species, and finally one miRNA-sibling of a soybean conserved miRNA. Conserved and novel miRNAs were evaluated by RT-qPCR. We observed a differential expression across the three whorls for six miRNAs. Computational predicted targets for miRNAs analyzed by RT-qPCR were identified and present functions related to reproductive process in plants. In summary, the increased accumulation of specific and novel miRNAs in different whorls indicates that miRNAs are an important part of the regulatory network in soybean flower.