miR2118-triggered phased siRNAs are differentially expressed during the panicle development of wild and domesticated African rice species

Functional role of microRNA in the regulation of biotic and abiotic stress in agronomic plants

The increasing demand for food is the result of an increasing population. It is crucial to enhance crop yield for sustainable production. Recently, microRNAs (miRNAs) have gained importance because of their involvement in crop productivity by regulating gene transcription in numerous biological processes, such as growth, development and abiotic and biotic stresses. miRNAs are small, non-coding RNA involved in numerous other biological functions in a plant that range from genomic integrity, metabolism, growth, and development to environmental stress response, which collectively influence the agronomic traits of the crop species. Additionally, miRNA families associated with various agronomic properties are conserved across diverse plant species. The miRNA adaptive responses enhance the plants to survive environmental stresses, such as drought, salinity, cold, and heat conditions, as well as biotic stresses, such as pathogens and insect pests. Thus, understanding the detailed mechanism of the potential response of miRNAs during stress response is necessary to promote the agronomic traits of crops. In this review, we updated the details of the functional aspects of miRNAs as potential regulators of various stress-related responses in agronomic plants.

Genome-wide association analysis identifies natural allelic variants associated with panicle architecture variation in African rice, Oryza glaberrima Steud

African rice (Oryza glaberrima Steud), a short-day cereal crop closely related to Asian rice (Oryza sativa L.), has been cultivated in Sub-Saharan Africa for ∼ 3,000 years. Although less cultivated globally, it is a valuable genetic resource in creating high-yielding cultivars that are better adapted to diverse biotic and abiotic stresses. While inflorescence architecture, a key trait for rice grain yield improvement, has been extensively studied in Asian rice, the morphological and genetic determinants of this complex trait are less understood in African rice. In this study, using a previously developed association panel of 162 O. glaberrima accessions and new SNP variants characterized through mapping to a new version of the O. glaberrima reference genome, we conducted a genome-wide association study of four major morphological panicle traits. We have found a total of 41 stable genomic regions that are significantly associated with these traits, of which 13 co-localized with previously identified QTLs in O. sativa populations and 28 were unique for this association panel. Additionally, we found a genomic region of interest on chromosome 3 that was associated with the number of spikelets and primary and secondary branches. Within this region was localized the O. sativa ortholog of the PHYTOCHROME B gene (Oglab_006903/OgPHYB). Haplotype analysis revealed the occurrence of natural sequence variants at the OgPHYB locus associated with panicle architecture variation through modulation of the flowering time phenotype, whereas no equivalent alleles were found in O. sativa. The identification in this study of genomic regions specific to O. glaberrima indicates panicle-related intra-specific genetic variation in this species, increasing our understanding of the underlying molecular processes governing panicle architecture. Identified candidate genes and major haplotypes may facilitate the breeding of new African rice cultivars with preferred panicle traits.

Revitalizing miRNAs mediated agronomical advantageous traits improvement in rice

One of the key enigmas in conventional and modern crop improvement programmes is how to introduce beneficial traits without any penalty impairment. Rice (Oryza sativa L.), among the essential staple food crops grown and utilized worldwide, needs to improve genotypes in multifaceted ways. With the global view to feed ten billion under the climatic perturbation, only a potent functional master regulator can withstand with hope for the next green revolution and food security. miRNAs are such, miniature, fine tuners for crop improvement and provide a value addition in emerging technologies, namely large-scale genotyping, phenotyping, genome editing, marker-assisted selection, and genomic selection, to make rice production feasible. There has been surplus research output generated since the last decade on miRNAs in rice, however, recent functional knowledge is limited to reaping the benefits for conventional and modern improvements in rice to avoid ambiguity and redundancy in the generated data. Here, we present the latest functional understanding of miRNAs in rice. In addition, their biogenesis, intra- and inter-kingdom signaling and communication, implication of amiRNAs, and consequences upon integration with CRISPR-Cas9. Further, highlights refer to the application of miRNAs for rice agronomical trait improvements, broadly classified into three functional domains. The majority of functionally established miRNAs are responsible for growth and development, followed by biotic and abiotic stresses. Tabular cataloguing reveals and highlights two multifaceted modules that were extensively studied. These belong to miRNA families 156 and 396, orchestrate multifarious aspects of advantageous agronomical traits. Moreover, updated and exhaustive functional aspects of different supplemental miRNA modules that would strengthen rice improvement are also being discussed.

An insight into the roles of regulatory ncRNAs in plants: An abiotic stress and developmental perspective

Different environmental cues lead to changes in physiology, biochemistry and molecular status of plant's growth. Till date, various genes have been accounted for their role in regulating plant development and response to abiotic stress. Excluding genes that code for a functional protein in a cell, a large chunk of the eukaryotic transcriptome consists of non-coding RNAs (ncRNAs) which lack protein coding capacity but are still functional. Recent advancements in Next Generation Sequencing (NGS) technology have led to the unearthing of different types of small and large non-coding RNAs in plants. Non-coding RNAs are broadly categorised into housekeeping ncRNAs and regulatory ncRNAs which work at transcriptional, post-transcriptional and epigenetic levels. Diverse ncRNAs play different regulatory roles in nearly all biological processes including growth, development and response to changing environments. This response can be perceived and counteracted by plants using diverse evolutionarily conserved ncRNAs like miRNAs, siRNAs and lncRNAs to participate in complex molecular regimes by activating gene-ncRNA-mRNA regulatory modules to perform the downstream function. Here, we review the current understanding with a focus on recent advancements in the functional studies of the regulatory ncRNAs at the nexus of abiotic stresses and development. Also, the potential roles of ncRNAs in imparting abiotic stress tolerance and yield improvement in crop plants are also discussed with their future prospects.

The ABC of Flower Development in Monocots: The Model of Rice Spikelet

The initial seminal studies of flower developmental genetics were made from observations in several eudicot model species, particularly Arabidopsis and Antirrhinum. However, an increasing amount of research in monocot model and crop species is finally giving the credit that monocots deserve for their position in the evolutionary history of Angiosperms, their astonishing diversification and adaptation, their diversified floral structures, their pivotal function in most ecosystems on Earth and, finally, their importance in agriculture and farming, economy, landscaping and feeding mankind. Rice is a staple crop and the major monocot model to study the reproductive phase and flower evolution. Inspired by this, this chapter reviews a story of highly conserved functions related to the ABC model of flower development. Nevertheless, this model is complicated in rice by cases of gene neofunctionalization, like the recruitment of MADS-box genes for the development of the unique organs known as lemma and palea, subfunctionalization, and rewiring of conserved molecular pathways.

3D Imaging and In Situ Hybridization for Uncovering the Functions of MicroRNA in Rice Anther

Small RNAs specifically expressed in reproductive tissues are key regulators of germline development in eukaryotes. Rice microRNA2118 (miR2118), which is enriched during reproduction in grasses, is a trigger to produce phased small interfering RNAs (phasiRNAs). These phasiRNAs demonstrate the temporal regulation with premeiotic phasiRNAs and meiotic phasiRNAs in anther development. Furthermore, the site-specific regulation via miR2118 and phasiRNAs is of importance in soma and germ development in anthers. Accordingly, histological imaging methods are essential tools for understanding spatiotemporal regulation during reproduction and elucidating the reproductive roles of miRNAs and phasiRNAs. We successfully developed a method to visualize the three-dimensional (3D) structure of entire rice anthers, which can also be used for distinguishing the internal structure of the anthers in other plants. Here, we describe the detailed methods of in situ hybridization for miR2118 localization and the visualization of the 3D structure of entire anthers of rice.

Mechanism for the genomic and functional evolution of the MIR2118 family in the grass lineage

The MIR2118 family has undergone tremendous expansion in the grass lineage, in which the miRNA targets numerous noncoding PHAS loci to produce 21-nt phased small interfering RNAs (phasiRNAs) involved in male fertility. However, the evolutionary trajectory of the grass MIR2118 genes and the functions of phasiRNAs have not yet been fully elucidated. We conducted comparative genomic, molecular evolution, expression and parallel analysis of RNA ends (PARE) analyses of MIR2118 and the miR2118-mediated regulatory pathway in grasses, focusing on Oryza sativa. In total, 617 MIR2118 and eight MIR1859 novel members were identified. Phylogenetic analyses showed that grass MIR2118 genes form a distinct clade from the MIR482/2118 genes of nongrass species. We reconstructed hypothetical evolutionary histories of the grass MIR2118 clusters and its MIR1859 variants, and examined the polycistronic composition and the differential expression of the osa-MIR2118 clusters. PARE data showed that osa-miR2118 might also direct the cleavage of some protein-coding gene transcripts. Importantly, we found that PARE analysis is inherently prone to false-positive target predictions when a large number of small RNAs, such as phasiRNAs, are analysed. Our results revealed the evolution and diversification of the MIR2118 family, and provide new insights into the functions of phasiRNAs in the grasses.

Rice SEPALLATA genes OsMADS5 and OsMADS34 cooperate to limit inflorescence branching by repressing the TERMINAL FLOWER1-like gene RCN4

The spatiotemporal control of meristem identity is critical for determining inflorescence architecture, and thus yield, of cereal plants. However, the precise mechanisms underlying inflorescence and spikelet meristem determinacy in cereals are still largely unclear. We have generated loss-of-function and overexpression mutants of the paralogous OsMADS5 and OsMADS34 genes in rice (Oryza sativa), and analysed their panicle phenotypes. Using chromatin immunoprecipitation, electrophoretic mobility-shift and dual-luciferase assays, we have also identified RICE CENTRORADIALIS 4 (RCN4), a TFL1-like gene, as a direct downstream target of both OsMADS proteins, and have analysed RCN4 mutants. The osmads5 osmads34 mutant lines had significantly enhanced panicle branching with increased secondary, and even tertiary and quaternary, branches, compared to wild-type (WT) and osmads34 plants. The osmads34 mutant phenotype could largely be rescued by also knocking out RCN4. Moreover, transgenic panicles overexpressing RCN4 had significantly increased branching, and initiated development of c. 7× more spikelets than WT. Our results reveal a role for OsMADS5 in panicle development, and show that OsMADS5 and OsMADS34 play similar functions in limiting branching and promoting the transition to spikelet meristem identity, in part by repressing RCN4 expression. These findings provide new insights to better understand the molecular regulation of rice inflorescence architecture.

Spatiotemporal regulation and roles of reproductive phasiRNAs in plants

Since co-suppression was discovered as a pioneer silencing phenomenon of RNA interference (RNAi) in petunia in 1990, many types of small RNAs have been identified in the RNAi pathway among various eukaryotes. In plants, a large number of 21- or 24-nucleotide (nt) phased small interfering RNAs (phasiRNAs) are produced via processing of long RNA precursors by Dicer-like proteins. However, the roles of phasiRNAs remain largely unknown. The development of imaging technology and RNA profiling has clarified the spatiotemporal regulation of phasiRNAs, and subsequently the different functions of 21-nt trans-acting phasiRNAs and 24-nt cis-regulatory phasiRNAs during male organ development. This review focuses on the biogenesis, diversification, spatiotemporal expression pattern and function of phasiRNAs in plants.

PhasiRNAnalyzer: an integrated analyser for plant phased siRNAs

Phased siRNAs (phasiRNAs) are a class of small interfering RNAs (siRNAs) which play essential roles in plant development and defence. However, only a few phasiRNAs have been extensively studied due to the difficulties in identifying and characterizing plant phasiRNAs by plant biologists. Herein, we describe a comprehensive and multi-functional web server termed PhasiRNAnalyzer, which is able to identify all crucial components in plant phasiRNA's regulatory pathway (phase-initiator→PHAS gene→phasiRNA cluster→target gene). Currently, PhasiRNAnalyzer exhibits the following advantages: I) It is the most comprehensive platform which hosts 170 plant species with 256 genome data, 438 cDNA data and 271 degradome data. II) It can identify all crucial components in phasiRNA's regulatory pathway, and verify the interactions between phasiRNAs and their target genes based on degradome data. III) It can perform differential expression analysis of phasiRNAs on each PHAS gene locus between different samples conveniently. IV) It provides the user-friendly interfaces and introduces several improvements, primarily by making more accurate and efficient analysis when dealing with deep sequencing data. In summary, PhasiRNAnalyzer is a comprehensive and systemic phasiRNA analysis server with high sensitivity and efficiency. It can be freely accessed at https://cbi.njau.edu.cn/PPSA/.

Genome-Wide Analysis Identified a Set of Conserved lncRNAs Associated with Domestication-Related Traits in Rice

Crop domestication, which gives rise to a number of desirable agronomic traits, represents a typical model system of plant evolution. Numerous genomic evidence has proven that noncoding RNAs such as microRNAs and phasiRNAs, as well as protein-coding genes, are selected during crop domestication. However, limited data shows plant long noncoding RNAs (lncRNAs) are also involved in this biological process. In this study, we performed strand-specific RNA sequencing of cultivated rice Oryza sativa ssp. japonica and O. sativa ssp. indica, and their wild progenitor O. rufipogon. We identified a total of 8528 lncRNAs, including 4072 lncRNAs in O. rufipogon, 2091 lncRNAs in japonica rice, and 2365 lncRNAs in indica rice. The lncRNAs expressed in wild rice were revealed to be shorter in length and had fewer exon numbers when compared with lncRNAs from cultivated rice. We also identified a number of conserved lncRNAs in the wild and cultivated rice. The functional study demonstrated that several of these conserved lncRNAs are associated with domestication-related traits in rice. Our findings revealed the feature and conservation of lncRNAs during rice domestication and will further promote functional studies of lncRNAs in rice.

Role of phasiRNAs from two distinct phasing frames of GhMYB2 loci in cis- gene regulation in the cotton genome

BACKGROUND

Phased small interfering RNA (phasiRNA) is primarily derived from the 22-nt miRNA targeting loci. GhMYB2, a gene with potential roles in cotton fiber cell fate determination, is a target gene of miR828 and miR858 in the generation of phasiRNAs.

RESULTS

In the presented work, through the evaluation of phasing scores and phasiRNA distribution pattern, we found that phasiRNAs from GhMYB2 were derived from the 3' cleavage fragments of 22-nt miR828 and 21-nt miR858 respectively. These two miRNA targeting sites initiated two phasing frames on transcripts of one locus. By means of RNA ligase-mediated rapid amplification of cDNA ends (RLM-RACE), we further demonstrated that phasiRNAs derived from the two phasing frames played a role in cis-regulation of GhMYB2. The phasiRNAs derived from GhMYB2 were expressed in the somatic tissues, especially in anther and hypocotyl. We further employed our previous small RNA sequencing data as well as the degradome data of cotton fiber bearing ovules, anthers, hypocotyls and embryogenic calli tissues published in public databases, to validate the expression, phasing pattern and functions of phasiRNAs.

CONCLUSIONS

The presenting research provide insights of the molecular mechanism of phasiRNAs in regulation of GhMYB2 loci.

Loss of function of Oryza sativa Argonaute 18 induces male sterility and reduction in phased small RNAs

In this manuscript, we show that Oryza sativa indica Argonaute protein AGO18 is required for male gametophyte development likely to through a small RNA-mediated mechanism. Monocots have evolved unique gene silencing pathways due to the presence of unique members of Dicer-like and Argonaute (AGO) family members. Among the monocot AGO homologs, AGO18 occupies a unique position. Previous reports have implicated this protein in viral resistance as well as in gametogenesis, likely through its competition with AGO1 clade members for micro(mi)RNAs and other small (s)RNAs. Although expression of rice AGO18 in specific stages of male gametogenesis has been documented, its major functions in plant development remain poorly understood. Here, we show that Oryza sativa indica AGO18 is involved in male gametophyte development. Knockdown (KD) of AGO18 in transgenic rice lines resulted in stunted plants that are male sterile, whereas their carpels were functional. Transcriptome analysis revealed downregulation of several pollen development-associated genes in KD lines. sRNA sequencing in vegetative and reproductive tissues of KD lines indicated reduction of miRNAs and phased secondary sRNAs implicated in male gametophyte development. Our results indicate a distinct role for rice AGO18 in male fertility.

Advances in Molecular Genetics and Genomics of African Rice (Oryza glaberrima Steud)

African rice (Oryza glaberrima) has a pool of genes for resistance to diverse biotic and abiotic stresses, making it an important genetic resource for rice improvement. African rice has potential for breeding for climate resilience and adapting rice cultivation to climate change. Over the last decade, there have been tremendous technological and analytical advances in genomics that have dramatically altered the landscape of rice research. Here we review the remarkable advances in knowledge that have been witnessed in the last few years in the area of genetics and genomics of African rice. Advances in cheap DNA sequencing technologies have fuelled development of numerous genomic and transcriptomic resources. Genomics has been pivotal in elucidating the genetic architecture of important traits thereby providing a basis for unlocking important trait variation. Whole genome re-sequencing studies have provided great insights on the domestication process, though key studies continue giving conflicting conclusions and theories. However, the genomic resources of African rice appear to be under-utilized as there seems to be little evidence that these vast resources are being productively exploited for example in practical rice improvement programmes. Challenges in deploying African rice genetic resources in rice improvement and the genomics efforts made in addressing them are highlighted.

Traversing the Links between Heavy Metal Stress and Plant Signaling

Plants confront multifarious environmental stresses widely divided into abiotic and biotic stresses, of which heavy metal stress represents one of the most damaging abiotic stresses. Heavy metals cause toxicity by targeting crucial molecules and vital processes in the plant cell. One of the approaches by which heavy metals act in plants is by over production of reactive oxygen species (ROS) either directly or indirectly. Plants act against such overdose of metal in the environment by boosting the defense responses like metal chelation, sequestration into vacuole, regulation of metal intake by transporters, and intensification of antioxidative mechanisms. This response shown by plants is the result of intricate signaling networks functioning in the cell in order to transmit the extracellular stimuli into an intracellular response. The crucial signaling components involved are calcium signaling, hormone signaling, and mitogen activated protein kinase (MAPK) signaling that are discussed in this review. Apart from signaling components other regulators like microRNAs and transcription factors also have a major contribution in regulating heavy metal stress. This review demonstrates the key role of MAPKs in synchronously controlling the other signaling components and regulators in metal stress. Further, attempts have been made to focus on metal transporters and chelators that are regulated by MAPK signaling.

Non-coding RNAs and plant male sterility: current knowledge and future prospects

Latest outcomes assign functional role to non-coding (nc) RNA molecules in regulatory networks that confer male sterility to plants. Male sterility in plants offers great opportunity for improving crop performance through application of hybrid technology. In this respect, cytoplasmic male sterility (CMS) and sterility induced by photoperiod (PGMS)/temperature (TGMS) have greatly facilitated development of high-yielding hybrids in crops. Participation of non-coding (nc) RNA molecules in plant reproductive development is increasingly becoming evident. Recent breakthroughs in rice definitively associate ncRNAs with PGMS and TGMS. In case of CMS, the exact mechanism through which the mitochondrial ORFs exert influence on the development of male gametophyte remains obscure in several crops. High-throughput sequencing has enabled genome-wide discovery and validation of these regulatory molecules and their target genes, describing their potential roles performed in relation to CMS. Discovery of ncRNA localized in plant mtDNA with its possible implication in CMS induction is intriguing in this respect. Still, conclusive evidences linking ncRNA with CMS phenotypes are currently unavailable, demanding complementing genetic approaches like transgenics to substantiate the preliminary findings. Here, we review the recent literature on the contribution of ncRNAs in conferring male sterility to plants, with an emphasis on microRNAs. Also, we present a perspective on improved understanding about ncRNA-mediated regulatory pathways that control male sterility in plants. A refined understanding of plant male sterility would strengthen crop hybrid industry to deliver hybrids with improved performance.

De Novo Assemblies of Three Oryza glaberrima Accessions Provide First Insights about Pan-Genome of African Rices

Oryza glaberrima is one of the two cultivated species of rice, and harbors various interesting agronomic traits, especially in biotic and abiotic resistance, compared with its Asian cousin O. sativa. A previous reference genome was published but newer studies highlighted some missing parts. Moreover, global species diversity is known nowadays to be represented by more than one single individual. For that purpose, we sequenced, assembled and annotated de novo three different cultivars from O. glaberrima. After validating our assemblies, we were able to better solve complex regions than the previous assembly and to provide a first insight in pan-genomic divergence between individuals. The three assemblies shown large common regions, but almost 25% of the genome present collinearity breakpoints or are even individual specific.

Grass phasiRNAs and male fertility

Recent studies have indicated that a special type of small noncoding RNAs, phased small-interfering RNAs (phasiRNAs) play crucial roles in many cellular processes of plant development. PhasiRNAs are generated from long RNA precursors at intervals of 21 or 24 nt in plants, and they are produced from both protein-coding gene and long noncoding RNA genes. Different from those in eudicots, grass phasiRNAs include a special class of small RNAs that are specifically expressed in reproductive organs. These grass phasiRNAs are associated with gametogenesis, especially with anther development and male fertility. In this review, we summarized current knowledge on these small noncoding RNAs in male germ cells and their possible biological functions and mechanisms in grass species.

Response of microRNAs to cold treatment in the young spikes of common wheat

Background

MicroRNAs (miRNAs) are a class of small non-coding RNAs that play important roles in biotic and abiotic stresses by regulating their target genes. For common wheat, spring frost damage frequently occurs, especially when low temperature coincides with plants at early floral organ differentiation, which may result in significant yield loss. Up to date, the role of miRNAs in wheat response to frost stress is not well understood.

Results

We report here the sequencing of small RNA transcriptomes from the young spikes that were treated with cold stress and the comparative analysis with those of the control. A total of 192 conserved miRNAs from 105 families and nine novel miRNAs were identified. Among them, 34 conserved and five novel miRNAs were differentially expressed between the cold-stressed samples and the controls. The expression patterns of 18 miRNAs were further validated by quantitative real time polymerase chain reaction (qRT-PCR). Moreover, nearly half of the miRNAs were cross inducible by biotic and abiotic stresses when compared with previously published work. Target genes were predicted and validated by degradome sequencing. Gene Ontology (GO) enrichment analysis showed that the target genes of differentially expressed miRNAs were enriched for response to the stimulus, regulation of transcription, and ion transport functions. Since many targets of differentially expressed miRNAs were transcription factors that are associated with floral development such as ARF, SPB (Squamosa Promoter Binding like protein), MADS-box (MCM1, AG, DEFA and SRF), MYB, SPX (SYG1, Pho81 and XPR1), TCP (TEOSINTE BRANCHED, Cycloidea and PCF), and PPR (PentatricoPeptide Repeat) genes, cold-altered miRNA expression may cause abnormal reproductive organ development.

Conclusion

Analysis of small RNA transcriptomes and their target genes provide new insight into miRNA regulation in developing wheat inflorescences under cold stress. MiRNAs provide another layer of gene regulation in cold stress response that can be genetically manipulated to reduce yield loss in wheat.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3556-2) contains supplementary material, which is available to authorized users.

Differences in meristem size and expression of branching genes are associated with variation in panicle phenotype in wild and domesticated African rice

Background

The African rice Oryza glaberrima was domesticated from its wild relative Oryza barthii about 3000 years ago. During the domestication process, panicle complexity changed from a panicle with low complexity in O. barthii, to a highly branched panicle carrying more seeds in O. glaberrima. To understand the basis of this differential panicle development between the two species, we conducted morphological and molecular analyses of early panicle development.

Results

Using X-ray tomography, we analyzed the morphological basis of early developmental stages of panicle development. We uncovered evidence for a wider rachis meristem in O. glaberrima than in O. barthii. At the molecular level, spatial and temporal expression profiles of orthologs of O. sativa genes related to meristem activity and meristem fate control were obtained using in situ hybridization and qRT-PCR. Despite highly conserved spatial expression patterns between O. glaberrima and O. barthii, differences in the expression levels of these early acting genes were detected.

Conclusion

The higher complexity of the O. glaberrima panicle compared to that of its wild relative O. barthii is associated with a wider rachis meristem and a modification of expression of branching-related genes. Our study indicates that the expression of genes in the miR156/miR529/SPL and TAW1 pathways, along with that of their target genes, is altered from the unbranched stage of development. This suggests that differences in panicle complexity between the two African rice species result from early alterations to gene expression during reproductive development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13227-017-0065-y) contains supplementary material, which is available to authorized users.

Biogenesis of diverse plant phasiRNAs involves an miRNA-trigger and Dicer-processing

It has been almost 30 years since RNA interference (RNAi) was shown to silence genes via double-stranded RNAs (dsRNAs) in Caenorhabditis elegans (Fire et al. 1998). 20-30-nucleotide (nt) small non-coding RNAs are a key element of the RNAi machinery. Recently, phased small interfering RNAs (phasiRNAs), small RNAs that are generated from a long RNA precursor at intervals of 21 to 26-nt, have been identified in plants and animals. In Drosophila, phasiRNAs are generated by the endonuclease, Zucchini (Zuc), in germlines. These phasiRNAs, known as one of PIWI-interacting RNAs (piRNAs), mainly repress transposable elements. Similarly, reproduction-specific phasiRNAs have been identified in the family Poaceae, although DICER LIKE (DCL) protein-dependent phasiRNA biogenesis in rice is distinct from piRNA biogenesis in animals. In plants, phasiRNA biogenesis is initiated when 22-nt microRNAs (miRNAs) cleave single-stranded target RNAs. Subsequently, RNA-dependent RNA polymerase (RDR) forms dsRNAs from the cleaved RNAs, and dsRNAs are further processed by DCLs into 21 to 24-nt phasiRNAs. Finally, the phasiRNAs are loaded to ARGONAUTE (AGO) proteins to induce RNA-silencing. There are diverse types of phasiRNA precursors and the miRNAs that trigger the biogenesis. Their expression patterns also differ among plant species, suggesting that species-specific combinations of these triggers dictate the spatio-temporal pattern of phasiRNA biogenesis during development, or in response to environmental stimuli.