Genomic Analysis of MicroRNA Promoters and Their Cis-Acting Elements in Soybean

Advances in the Study of the Transcriptional Regulation Mechanism of Plant miRNAs

MicroRNAs (miRNA) are a class of endogenous, non-coding, small RNAs with about 22 nucleotides (nt), that are widespread in plants and are involved in various biological processes, such as development, flowering phase transition, hormone signal transduction, and stress response. The transcriptional regulation of miRNAs is an important process of miRNA gene regulation, and it is essential for miRNA biosynthesis and function. Like mRNAs, miRNAs are transcribed by RNA polymerase II, and these transcription processes are regulated by various transcription factors and other proteins. Consequently, the upstream genes regulating miRNA transcription, their specific expression, and the regulating mechanism were reviewed to provide more information for further research on the miRNA regulatory mechanism and help to further understand the regulatory networks of plant miRNAs.

Endogenous small RNA clusters in plants

In plants, small RNAs (sRNAs) usually refer to non-coding RNAs (ncRNAs) with lengths of 20–24 nucleotides. sRNAs are involved in the regulation of many essential processes related to plant development and environmental responses. sRNAs in plants are mainly grouped into microRNAs (miRNAs) and small interfering RNAs (siRNAs), and the latter can be further classified into trans-acting siRNAs (ta-siRNAs), repeat-associated siRNAs (ra-siRNAs), natural anti-sense siRNAs (nat-siRNAs), etc. Many sRNAs exhibit a clustered distribution pattern in the genome. Here, we summarize the features and functions of cluster-distributed sRNAs, aimed to not only provide a thorough picture of sRNA clusters (SRCs) in plants, but also shed light on the identification of new classes of functional sRNAs.

Analysis of promoters of microRNAs from a Glycine max degradome library

OBJECTIVE

MicroRNAs (miRNAs) are genome-encoded, small non-coding RNAs that play important functions in development, biotic and abiotic stress responses, and other processes. Our aim was to explore the regulation of miRNA expression.

METHODS

We used bioinformatics methods to predict the core promoters of 440 miRNAs identified from a soybean (Glycine max) degradome library and to analyze cis-acting elements for 369 miRNAs.

RESULTS

The prediction results showed that 83.86% of the 440 miRNAs contained promoters in their upstream sequences, and 8.64% (38 loci) in their downstream sequences. The distributions of two core promoter elements, TATA-boxes and transcription start sites (TSSs), were similar. The cis-acting elements were examined to provide clues to the function and regulation of spatiotemporal expression of the miRNAs. Analyses of miRNA cis-elements and targets indicated a potential auxin response factor (ARF)- and gibberellin response factor (GARF)-mediated negative feedback loop for miRNA expression.

CONCLUSIONS

The features of miRNAs from a Glycine max degradome library obtained here provide insights into the transcription regulation and functions of miRNAs in soybean.