Overview of miRNA biogenesis and applications in plants

Mechanism of action of microRNA166 on nitric oxide in alfalfa (Medicago sativa L.) under drought stress

BACKGROUND

Alfalfa is a perennial forage crop of high importance, but its cultivation is often affected by drought stress. Currently, the investigation of drought-related small RNAs is a popular research topic to uncover plant drought resistance mechanisms. Among these small RNAs, microRNA166 (miR166) is associated with drought in numerous plant species. Initial small RNA sequencing studies have shown that miR166 is highly responsive to exogenous nitric oxide (NO) and drought. Therefore, analyzing the expression of Msa-miR166 under nitric oxide and drought treatment is significant.

RESULT

Bioinformatics analysis revealed that the miR166 family is widely distributed among plants, ranging from mosses to eudicots, with significant distribution differences between species. The evolutionary degree of Msa-miR166s is highly similar to that of Barrel medic (Medicago truncatula) and Soybean (Glycine max), but significantly different from the model plant Arabidopsis (Arabidopsis thaliana). It is suggested that there are no significant differences in miR166s within the species, and members of Msa-miR166s can form a typical stem-loop. The lowest level of exogenous nitric oxide was observed in Msa-miR166s under drought stress, followed by individual drought, and the highest level was observed after removing endogenous nitric oxide.

CONCLUSION

In response to short-term drought, Msa-miR166s down-regulate expression in alfalfa (Medicago sativa L.). Exogenous nitric oxide can reduce the expression of Msa-miR166s in response to short-term drought. These findings suggest that Msa-miR166e-5p is responsive to environmental changes. The expression levels of target genes showed an opposite trend to Msa-miR166s, verifying the accuracy of Degradome sequencing in the early stage. This suggests that alfalfa experiences drought stress when regulated by exogenous nitric oxide, targeting HD ZIP-III, FRI, and CoA ligase genes. Additionally, the expression of Msa-miR166s in response to drought stress varies between leaves and roots, indicating spatiotemporal specificity.

FvemiR160-FveARF18A-FveAP1/FveFUL module regulates flowering time in woodland strawberry

Flowering is an indicator of plant transformation from vegetative to reproductive growth. miR160 has been shown to have a significant effect on the growth and development of fruits, leaves, and roots of plants or their stress response to environment, but the participation of miR160 in regulating flowering time in plants is unclear. In this study, we found that two FvemiR160s (FvemiR160a/FvemiR160b) mature sequences in strawberry (Fragaria vesca) were consistent. It was displayed that the miR160 mature sequence is highly conserved in various species, and the miR160 mature sequence formed by the 5' arm of the MIR160 precursor was more conserved. Three FveARFs in woodland strawberry were negatively regulated by FvemiR160a, among which FveARF18A was the most significant. Phylogenetic analysis indicated that FvemiR160 is closely related to apple (Malus domestica), grape (Vitis vinifera), and Arabidopsis thaliana, while FveARF18A is closely related to RcARF18. Subsequently, we demonstrated that FvemiR160a can target cutting FveARF18A to negatively regulate its expression by RLM-5' RACE, cleavage site mutation, and GFP fluorescence assay. Moreover, we observed that FveMIR160a overexpressed plants have advanced flowering, while mFveARF18A overexpressed plants have delayed flowering. We also verified that FveARF18A negatively regulates the expression of FveAP1 and FveFUL by binding their promoters by yeast one-hybrid, LUC, and GUS assay, and FveAP1 and FveFUL transgenic Arabidopsis showed early flowering phenotype. In addition, the expression level of FvemiR160a was decreased obviously while that of FveARF18A was increased obviously by MeJA, GA and IAA. In conclusion, our study reveals the important role of the FvemiR160-FveARF18A-FveAP1/FveFUL module in the flowering process of woodland strawberry and provides a new pathway for studying flowering.

Genome-wide identification of the longan R2R3-MYB gene family and its role in primary and lateral root

R2R3-MYB is an important transcription factor family that regulates plant growth and development. Root development directly affects the absorption of water and nutrients by plants. Therefore, to understand the regulatory role of R2R3-MYB transcription factor family in root development of longan, this study identified the R2R3-MYB gene family members at the genome-wide level, and analyzed their phylogenetic characteristics, physical and chemical properties, gene structure, chromosome location and tissue expression. The analysis identified 124 R2R3-MYB family members in the longan genome. Phylogenetic analysis divided these members into 22 subfamilies, and the members of the unified subfamily had similar motifs and gene structures. The result of qRT-PCR showed that expression levels of DlMYB33, DlMYB34, DlMYB59, and DlMYB77 were significantly higher in main roots than in lateral as opposed to those of DlMYB35, DlMYB69, DlMYB70, and DlMYB83, which were significantly lower. SapBase database prediction and miRNAs sequencing results showed that 34 longan miRNAs could cleave R2R3-MYB, including 17 novel miRNAs unique to longan. The qRT-PCR and subcellular localization experiments of DlMYB92 and DlMYB98 showed that DlMYB92 is a key factor that regulates transcription in the nucleus and participates in the regulation of longan lateral root development. Longan also has a conserved miRNA-MYB-lateral root development regulation mechanism. This study provides a reference for further research on the transcriptional regulation of the miRNA-R2R3-MYB module in the root development of longan.

miRNAs for crop improvement

Climate change significantly impacts crop production by inducing several abiotic and biotic stresses. The increasing world population, and their food and industrial demands require focused efforts to improve crop plants to ensure sustainable food production. Among various modern biotechnological tools, microRNAs (miRNAs) are one of the fascinating tools available for crop improvement. miRNAs belong to a class of small non-coding RNAs playing crucial roles in numerous biological processes. miRNAs regulate gene expression by post-transcriptional target mRNA degradation or by translation repression. Plant miRNAs have essential roles in plant development and various biotic and abiotic stress tolerance. In this review, we provide propelling evidence from previous studies conducted around miRNAs and provide a one-stop review of progress made for breeding stress-smart future crop plants. Specifically, we provide a summary of reported miRNAs and their target genes for improvement of plant growth and development, and abiotic and biotic stress tolerance. We also highlight miRNA-mediated engineering for crop improvement and sequence-based technologies available for the identification of miRNAs associated with stress tolerance and plant developmental events.

Overview of Repressive miRNA Regulation by Short Tandem Target Mimic (STTM): Applications and Impact on Plant Biology

The application of miRNA mimic technology for silencing mature miRNA began in 2007. This technique originated from the discovery of the INDUCED BY PHOSPHATE STARVATION 1 (IPS1) gene, which was found to be a competitive mimic that prevents the cleavage of the targeted mRNA by miRNA inhibition at the post-transcriptional level. To date, various studies have been conducted to understand the molecular mimic mechanism and to improve the efficiency of this technology. As a result, several mimic tools have been developed: target mimicry (TM), short tandem target mimic (STTM), and molecular sponges (SPs). STTM is the most-developed tool due to its stability and effectiveness in decoying miRNA. This review discusses the application of STTM technology on the loss-of-function studies of miRNA and members from diverse plant species. A modified STTM approach for studying the function of miRNA with spatial-temporal expression under the control of specific promoters is further explored. STTM technology will enhance our understanding of the miRNA activity in plant-tissue-specific development and stress responses for applications in improving plant traits via miRNA regulation.