Investigation into the miRNA/5' isomiRNAs function and drought-mediated miRNA processing in rice

Switching action modes of miR408-5p mediates auxin signaling in rice

MicroRNAs (miRNAs) play fundamental roles in many developmental and physiological processes in eukaryotes. MiRNAs in plants generally regulate their targets via either mRNA cleavage or translation repression; however, which approach plays a major role and whether these two function modes can shift remains elusive. Here, we identify a miRNA, miR408-5p that regulates AUXIN/INDOLE ACETIC ACID 30 (IAA30), a critical repressor in the auxin pathway via switching action modes in rice. We find that miR408-5p usually inhibits IAA30 protein translation, but in a high auxin environment, it promotes the decay of IAA30 mRNA when it is overproduced. We further demonstrate that IDEAL PLANT ARCHITECTURE1 (IPA1), an SPL transcription factor regulated by miR156, mediates leaf inclination through association with miR408-5p precursor promoter. We finally show that the miR156-IPA1-miR408-5p-IAA30 module could be controlled by miR393, which silences auxin receptors. Together, our results define an alternative auxin transduction signaling pathway in rice that involves the switching of function modes by miR408-5p, which contributes to a better understanding of the action machinery as well as the cooperative network of miRNAs in plants.

Delineating the tissue-mediated drought stress governed tuning of conserved miR408 and its targets in rice

Engineering drought tolerance in rice needs to focus on regulators that enhance tolerance while boosting plant growth and vigor. The present study delineated the concealed function and tissue-mediated interplay of the miR408/target module in imparting drought stress tolerance in rice. The plant miR408 family comprises three dominant mature forms (21 nt), including a distinct monocot variant (F-7 with 5' C) and is divided into six groups. miR408 majorly cleaves genes belonging to the blue copper protein in addition to several other species-specific targets in plants. Comparative sequence analysis in 4726 rice accessions identified 22 sequence variants (SNP and InDELs) in its promoter (15) and pre-miR408 region. Haplotype analysis of the sequence variants indicated eight haplotypes (three: Japonica-specific and five: Indica-specific) of the miR408 promoter. In drought-tolerant Nagina 22, miR408 follows flag leaf preferential expression. Under drought conditions, its levels are upregulated in flag leaf and roots which seems to be regulated by a differential fraction of methylated cytosines (mCs) in the precursor region. The active pool of miR408 regulated targets under control and drought conditions is impacted by the tissue type. Comparative expression analysis of the miR408/target module under different sets of conditions features 83 targets exhibiting antagonistic expression in rice, out of which 12 genes, including four PLANTACYANINS (OsUCL6, 7, 9 and 30), PIRIN, OsLPR1, OsCHUP1, OsDOF12, OsBGLU1, glycine-rich cell wall gene, OsDUT, and OsERF7, are among the high confidence targets. Further, overexpression of MIR408 in drought-sensitive rice cultivar (PB1) leads to the massive enhancement of vegetative growth in rice with improved ETR and Y(II) and enhanced dehydration stress tolerance. The above results suggest that miR408 is likely to act as a positive regulator of growth and vigor, as well as dehydration stress, making it a potential candidate for engineering drought tolerance in rice.

Dynamic Regulation of Grapevine's microRNAs in Response to Mycorrhizal Symbiosis and High Temperature

MicroRNAs (miRNAs) are non-coding small RNAs that play crucial roles in plant development and stress responses and can regulate plant interactions with beneficial soil microorganisms such as arbuscular mycorrhizal fungi (AMF). To determine if root inoculation with distinct AMF species affected miRNA expression in grapevines subjected to high temperatures, RNA-seq was conducted in leaves of grapevines inoculated with either Rhizoglomus irregulare or Funneliformis mosseae and exposed to a high-temperature treatment (HTT) of 40 °C for 4 h per day for one week. Our results showed that mycorrhizal inoculation resulted in a better plant physiological response to HTT. Amongst the 195 identified miRNAs, 83 were considered isomiRs, suggesting that isomiRs can be biologically functional in plants. The number of differentially expressed miRNAs between temperatures was higher in mycorrhizal (28) than in non-inoculated plants (17). Several miR396 family members, which target homeobox-leucine zipper proteins, were only upregulated by HTT in mycorrhizal plants. Predicted targets of HTT-induced miRNAs in mycorrhizal plants queried to STRING DB formed networks for Cox complex, and growth and stress-related transcription factors such as SQUAMOSA promoter-binding-like-proteins, homeobox-leucine zipper proteins and auxin receptors. A further cluster related to DNA polymerase was found in R. irregulare inoculated plants. The results presented herein provide new insights into miRNA regulation in mycorrhizal grapevines under heat stress and can be the basis for functional studies of plant-AMF-stress interactions.

Unravelling the treasure trove of drought-responsive genes in wild-type peanut through transcriptomics and physiological analyses of root

Peanut is one of the most valuable legumes, grown mainly in arid and semi-arid regions, where its production may be hindered by the lack of water. Therefore, breeding drought tolerant varieties is of great importance for peanut breeding programs around the world. Unlike cultivated peanuts, wild peanuts have greater genetic diversity and are an important source of alleles conferring tolerance/resistance to abiotic and biotic stresses. To decipher the transcriptome changes under drought stress, transcriptomics of roots of highly tolerant Arachis duranensis (ADU) and moderately susceptible A. stenosperma (AST) genotypes were performed. Transcriptome analysis revealed an aggregate of 1465 differentially expressed genes (DEGs), and among the identified DEGs, there were 366 single nucleotide polymorphisms (SNPs). Gene ontology and Mapman analyses revealed that the ADU genotype had a higher number of transcripts related to DNA methylation or demethylation, phytohormone signal transduction and flavonoid production, transcription factors, and responses to ethylene. The transcriptome analysis was endorsed by qRT-PCR, which showed a strong correlation value (R² = 0.96). Physio-biochemical analysis showed that the drought-tolerant plants produced more osmolytes, ROS phagocytes, and sugars, but less MDA, thus attenuating the effects of drought stress. In addition, three SNPs of the gene encoding transcription factor NFAY (Aradu.YE2F8), expansin alpha (Aradu.78HGD), and cytokinin dehydrogenase 1-like (Aradu.U999X) exhibited polymorphism in selected different genotypes. Such SNPs could be useful for the selection of drought-tolerant genotypes.

Regulatory non-coding RNAs: a new frontier in regulation of plant biology

Beyond the most crucial roles of RNA molecules as a messenger, ribosomal, and transfer RNAs, the regulatory role of many non-coding RNAs (ncRNAs) in plant biology has been recognized. ncRNAs act as riboregulators by recognizing specific nucleic acid targets through homologous sequence interactions to regulate plant growth, development, and stress responses. Regulatory ncRNAs, ranging from small to long ncRNAs (lncRNAs), exert their control over a vast array of biological processes. Based on the mode of biogenesis and their function, ncRNAs evolved into different forms that include microRNAs (miRNAs), small interfering RNAs (siRNAs), miRNA variants (isomiRs), lncRNAs, circular RNAs (circRNAs), and derived ncRNAs. This article explains the different classes of ncRNAs and their role in plant development and stress responses. Furthermore, the applications of regulatory ncRNAs in crop improvement, targeting agriculturally important traits, have been discussed.

mi-IsoNet: systems-scale microRNA landscape reveals rampant isoform-mediated gain of target interaction diversity and signaling specificity

MicroRNA (miRNA) is not a single sequence, but a series of multiple variants (also termed isomiRs) with sequence and expression heterogeneity. Whether and how these isoforms contribute to functional variation and complexity at the systems and network levels remain largely unknown. To explore this question systematically, we comprehensively analyzed the expression of small RNAs and their target sites to interrogate functional variations between novel isomiRs and their canonical miRNA sequences. Our analyses of the pan-cancer landscape of miRNA expression indicate that multiple isomiRs generated from the same miRNA locus often exhibit remarkable variation in their sequence, expression and function. We interrogated abundant and differentially expressed 5' isomiRs with novel seed sequences via seed shifting and identified many potential novel targets of these 5' isomiRs that would expand interaction capabilities between small RNAs and mRNAs, rewiring regulatory networks and increasing signaling circuit complexity. Further analyses revealed that some miRNA loci might generate diverse dominant isomiRs that often involved isomiRs with varied seeds and arm-switching, suggesting a selective advantage of multiple isomiRs in regulating gene expression. Finally, experimental validation indicated that isomiRs with shifted seed sequences could regulate novel target mRNAs and therefore contribute to regulatory network rewiring. Our analysis uncovers a widespread expansion of isomiR and mRNA interaction networks compared with those seen in canonical small RNA analysis; this expansion suggests global gene regulation network perturbations by alternative small RNA variants or isoforms. Taken together, the variations in isomiRs that occur during miRNA processing and maturation are likely to play a far more complex and plastic role in gene regulation than previously anticipated.

Emerging Molecular Strategies for Improving Rice Drought Tolerance

Rice occupies a pre-eminent position as a food crop in the world. Its production, how- ever, entails up to 3000 liters of water per kilogram of grain produced. Such high demand makes rice prone to drought easily. Sustainable rice cultivation with limited water resources requires the deployment of a suitable strategy for better water use efficiency and improved drought tolerance. Several drought-related genes have been evaluated in rice for their mode of action in conferring drought tolerance. Manipulation of components of abscisic acid signal transduction, stomatal density, deposition of cuticular wax, and protein modification pathways are emerging as priority targets. Gene reprogramming by microRNAs is also being explored to achieve drought tolerance. Genetically dissected Quantitative Trait Loci (QTLs) and their constituent genes are being deployed to develop drought-tolerant rice varieties. Progressive research and challenges include a better understanding of crucial components of drought response and search for new targets and the deployment of improved varieties in the field.

Profiling of MicroRNAs and Their Targets in Roots and Shoots Reveals a Potential MiRNA-Mediated Interaction Network in Response to Phosphate Deficiency in the Forestry Tree Betula luminifera

Inorganic phosphate (Pi) is often lacking in natural and agro-climatic environments, which impedes the growth of economically important woody species. Plants have developed strategies to cope with low Pi (LP) availability. MicroRNAs (miRNAs) play important roles in responses to abiotic stresses, including nutrition stress, by regulating target gene expression. However, the miRNA-mediated regulation of these adaptive responses and their underlying coordinating signals are still poorly understood in forestry trees such as Betula luminifera. Transcriptomic libraries, small RNA (sRNA) libraries, and a mixed degradome cDNA library of B. luminifera roots and shoots treated under LP and normal conditions (CK) were constructed and sequenced using next-generation deep sequencing. A comprehensive B. luminifera transcriptome derived from its roots and shoots was constructed, and a total of 76,899 unigenes were generated. Analysis of the transcriptome identified 8,095 and 5,584 differentially expressed genes in roots and shoots, respectively, under LP conditions. sRNA sequencing analyses indicated that 66 and 60 miRNAs were differentially expressed in roots and shoots, respectively, under LP conditions. A total of 109 and 112 miRNA-target pairs were further validated in the roots and shoots, respectively, using degradome sequencing. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis of differential miRNA targets indicated that the "ascorbate and aldarate metabolism" pathway responded to LP, suggesting miRNA-target pairs might participating in the removing of reactive oxidative species under LP stress. Moreover, a putative network of miRNA-target interactions involved in responses to LP stress in B. luminifera is proposed. Taken together, these findings provide useful information to decipher miRNA functions and establish a framework for exploring P signaling networks regulated by miRNAs in B. luminifera and other woody plants. It may provide new insights into the genetic engineering of high use efficiency of Pi in forestry trees.