RESUMO
Argonaute proteins use single-stranded RNA or DNA guides to target complementary nucleic acids. This allows eukaryotic Argonaute proteins to mediate RNA interference and long prokaryotic Argonaute proteins to interfere with invading nucleic acids. The function and mechanisms of the phylogenetically distinct short prokaryotic Argonaute proteins remain poorly understood. We demonstrate that short prokaryotic Argonaute and the associated TIR-APAZ (SPARTA) proteins form heterodimeric complexes. Upon guide RNA-mediated target DNA binding, four SPARTA heterodimers form oligomers in which TIR domain-mediated NAD(P)ase activity is unleashed. When expressed in Escherichia coli, SPARTA is activated in the presence of highly transcribed multicopy plasmid DNA, which causes cell death through NAD(P)+ depletion. This results in the removal of plasmid-invaded cells from bacterial cultures. Furthermore, we show that SPARTA can be repurposed for the programmable detection of DNA sequences. In conclusion, our work identifies SPARTA as a prokaryotic immune system that reduces cell viability upon RNA-guided detection of invading DNA.
Assuntos
Proteínas Argonautas , Células Procarióticas/fisiologia , Proteínas Argonautas/metabolismo , DNA/metabolismo , Células Procarióticas/citologia , Células Procarióticas/metabolismo , RNA Guia de CinetoplastídeosRESUMO
Animals face both external and internal dangers: pathogens threaten from the environment, and unstable genomic elements threaten from within. C. elegans protects itself from pathogens by "reading" bacterial small RNAs, using this information to both induce avoidance and transmit memories for four generations. Here, we found that memories can be transferred from either lysed animals or from conditioned media to naive animals via Cer1 retrotransposon-encoded virus-like particles. Moreover, Cer1 functions internally at the step of transmission of information from the germline to neurons and is required for learned avoidance. The presence of the Cer1 retrotransposon in wild C. elegans strains correlates with the ability to learn and inherit small-RNA-induced pathogen avoidance. Together, these results suggest that C. elegans has co-opted a potentially dangerous retrotransposon to instead protect itself and its progeny from a common pathogen through its inter-tissue signaling ability, hijacking this genomic element for its own adaptive immunity benefit.
Assuntos
Elementos de DNA Transponíveis/genética , Transferência Genética Horizontal/genética , Padrões de Herança/genética , Memória/fisiologia , Animais , Aprendizagem da Esquiva , Comportamento Animal , Caenorhabditis elegans/genética , Caenorhabditis elegans/fisiologia , Vesículas Extracelulares/metabolismo , Regulação da Expressão Gênica , Genoma , Células Germinativas/metabolismo , RNA/metabolismo , Interferência de RNA , Vírion/metabolismoRESUMO
It is unknown whether the activity of the nervous system can be inherited. In Caenorhabditis elegans nematodes, parental responses can transmit heritable small RNAs that regulate gene expression transgenerationally. In this study, we show that a neuronal process can impact the next generations. Neurons-specific synthesis of RDE-4-dependent small RNAs regulates germline amplified endogenous small interfering RNAs (siRNAs) and germline gene expression for multiple generations. Further, the production of small RNAs in neurons controls the chemotaxis behavior of the progeny for at least three generations via the germline Argonaute HRDE-1. Among the targets of these small RNAs, we identified the conserved gene saeg-2, which is transgenerationally downregulated in the germline. Silencing of saeg-2 following neuronal small RNA biogenesis is required for chemotaxis under stress. Thus, we propose a small-RNA-based mechanism for communication of neuronal processes transgenerationally.
Assuntos
Comportamento Animal , Caenorhabditis elegans , Neurônios/metabolismo , RNA de Helmintos , Pequeno RNA não Traduzido , Animais , Proteínas Argonautas/genética , Proteínas Argonautas/metabolismo , Caenorhabditis elegans/citologia , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Neurônios/citologia , RNA de Helmintos/biossíntese , RNA de Helmintos/genética , Pequeno RNA não Traduzido/biossíntese , Pequeno RNA não Traduzido/genéticaRESUMO
Transposon reactivation is an inherent danger in cells that lose epigenetic silencing during developmental reprogramming. In the mouse, long terminal repeat (LTR)-retrotransposons, or endogenous retroviruses (ERV), account for most novel insertions and are expressed in the absence of histone H3 lysine 9 trimethylation in preimplantation stem cells. We found abundant 18 nt tRNA-derived small RNA (tRF) in these cells and ubiquitously expressed 22 nt tRFs that include the 3' terminal CCA of mature tRNAs and target the tRNA primer binding site (PBS) essential for ERV reverse transcription. We show that the two most active ERV families, IAP and MusD/ETn, are major targets and are strongly inhibited by tRFs in retrotransposition assays. 22 nt tRFs post-transcriptionally silence coding-competent ERVs, while 18 nt tRFs specifically interfere with reverse transcription and retrotransposon mobility. The PBS offers a unique target to specifically inhibit LTR-retrotransposons, and tRF-targeting is a potentially highly conserved mechanism of small RNA-mediated transposon control.
Assuntos
Inativação Gênica , Pequeno RNA não Traduzido/metabolismo , RNA de Transferência/metabolismo , Retroviridae/genética , Células-Tronco/virologia , Animais , Células HeLa , Humanos , Camundongos , Sequências Repetidas TerminaisRESUMO
In the ciliated protozoan Paramecium tetraurelia, Piwi-associated small RNAs are generated upon the elimination of tens of thousands of short transposon-derived DNA segments as part of development. These RNAs then target complementary DNA for elimination in a positive feedback process, contributing to germline defense and genome stability. In this work, we investigate the formation of these RNAs, which we show to be transcribed directly from the short (length mode 27 bp) excised DNA segments. Our data support a mechanism whereby the concatenation and circularization of excised DNA segments provides a template for RNA production. This process allows the generation of a double-stranded RNA for Dicer-like protein cleavage to give rise to a population of small regulatory RNAs that precisely match the excised DNA sequences. VIDEO ABSTRACT.
Assuntos
DNA Concatenado , Paramecium tetraurellia/genética , Núcleo Celular/metabolismo , DNA Ligase Dependente de ATP/metabolismo , Elementos de DNA Transponíveis , Exodesoxirribonucleases/metabolismo , Paramecium tetraurellia/citologia , Paramecium tetraurellia/metabolismo , RNA/genética , Transcrição GênicaRESUMO
Despite the numerous sequencing methods available, the diversity in RNA size and chemical modification makes it difficult to capture all RNAs in a cell. We developed a method that combines quasi-random priming with template switching to construct sequencing libraries from RNA molecules of any length and with any type of 3' modifications, allowing for the sequencing of virtually all RNA species. Our ligation-independent detection of all types of RNA (LIDAR) is a simple, effective tool to identify and quantify all classes of coding and non-coding RNAs. With LIDAR, we comprehensively characterized the transcriptomes of mouse embryonic stem cells, neural progenitor cells, mouse tissues, and sperm. LIDAR detected a much larger variety of tRNA-derived RNAs (tDRs) compared with traditional ligation-dependent sequencing methods and uncovered tDRs with blocked 3' ends that had previously escaped detection. Therefore, LIDAR can capture all RNAs in a sample and uncover RNA species with potential regulatory functions.
RESUMO
PIWI-clade Argonaute proteins associate with PIWI-interacting RNAs (piRNAs) and silence transposable elements in animal gonads. Here, we report the crystal structure of a silkworm PIWI-clade Argonaute, Siwi, bound to the endogenous piRNA, at 2.4 Å resolution. Siwi adopts a bilobed architecture consisting of N-PAZ and MID-PIWI lobes, in which the 5' and 3' ends of the bound piRNA are anchored by the MID-PIWI and PAZ domains, respectively. A structural comparison of Siwi with AGO-clade Argonautes reveals notable differences in their nucleic-acid-binding channels, likely reflecting the distinct lengths of their guide RNAs and their mechanistic differences in guide RNA loading and cleavage product release. In addition, the structure reveals that Siwi and prokaryotic, but not eukaryotic, AGO-clade Argonautes share unexpected similarities, such as metal-dependent 5'-phosphate recognition and a potential structural transition during the catalytic-tetrad formation. Overall, this study provides a critical starting point toward a mechanistic understanding of piRNA-mediated transposon silencing.
Assuntos
Proteínas Argonautas/química , Bombyx/metabolismo , Proteínas de Insetos/química , RNA Interferente Pequeno/química , Animais , Proteínas Argonautas/isolamento & purificação , Bombyx/química , Bombyx/genética , Linhagem Celular , Cristalografia por Raios X , Elementos de DNA Transponíveis/genética , Inativação Gênica , Humanos , Proteínas de Insetos/isolamento & purificação , Conformação de Ácido Nucleico , RNA Interferente Pequeno/isolamento & purificaçãoRESUMO
Multiple division cycles without growth are a characteristic feature of early embryogenesis. The female germline loads proteins and RNAs into oocytes to support these divisions, which lack many quality control mechanisms operating in somatic cells undergoing growth. Here, we describe a small RNA-Argonaute pathway that ensures early embryonic divisions in C. elegans by employing catalytic slicing activity to broadly tune, instead of silence, germline gene expression. Misregulation of one target, a kinesin-13 microtubule depolymerase, underlies a major phenotype associated with pathway loss. Tuning of target transcript levels is guided by the density of homologous small RNAs, whose generation must ultimately be related to target sequence. Thus, the tuning action of a small RNA-catalytic Argonaute pathway generates oocytes capable of supporting embryogenesis. We speculate that the specialized nature of germline chromatin led to the emergence of small RNA-catalytic Argonaute pathways in the female germline as a post-transcriptional control layer to optimize oocyte composition.
Assuntos
Caenorhabditis elegans/embriologia , Caenorhabditis elegans/metabolismo , Embrião não Mamífero/metabolismo , Redes e Vias Metabólicas , Oócitos/metabolismo , Animais , Proteínas Argonautas/metabolismo , Sequência de Bases , Caenorhabditis elegans/citologia , Proteínas de Caenorhabditis elegans/metabolismo , Divisão Celular , Embrião não Mamífero/citologia , Desenvolvimento Embrionário , Feminino , Cinesinas/metabolismo , Microtúbulos/metabolismo , Dados de Sequência Molecular , Processamento Pós-Transcricional do RNARESUMO
Small ribonucleoproteins (sRNPs) target nascent precursor RNAs to guide folding, modification, and splicing during transcription. Yet, rapid co-transcriptional folding of the RNA can mask sRNP sites, impeding target recognition and regulation. To examine how sRNPs target nascent RNAs, we monitored binding of bacterial Hfqâ DsrA sRNPs to rpoS transcripts using single-molecule co-localization co-transcriptional assembly (smCoCoA). We show that Hfqâ DsrA recursively samples the mRNA before transcription of the target site to poise it for base pairing with DsrA. We adapted smCoCoA to precisely measure when the target site is synthesized and revealed that Hfqâ DsrA often binds the mRNA during target site synthesis close to RNA polymerase (RNAP). We suggest that targeting transcripts near RNAP allows an sRNP to capture a site before the transcript folds, providing a kinetic advantage over post-transcriptional targeting. We propose that other sRNPs may also use RNAP-proximal targeting to hasten recognition and regulation.
Assuntos
Proteínas de Escherichia coli , Pequeno RNA não Traduzido , Proteínas de Bactérias/metabolismo , Pequeno RNA não Traduzido/genética , Pequeno RNA não Traduzido/metabolismo , Escherichia coli/genética , Escherichia coli/metabolismo , RNA Mensageiro/metabolismo , Pareamento de Bases , RNA Bacteriano/metabolismo , Fator Proteico 1 do Hospedeiro/genética , Fator Proteico 1 do Hospedeiro/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Regulação Bacteriana da Expressão GênicaRESUMO
tRNA function is based on unique structures that enable mRNA decoding using anticodon trinucleotides. These structures interact with specific aminoacyl-tRNA synthetases and ribosomes using 3D shape and sequence signatures. Beyond translation, tRNAs serve as versatile signaling molecules interacting with other RNAs and proteins. Through evolutionary processes, tRNA fragmentation emerges as not merely random degradation but an act of recreation, generating specific shorter molecules called tRNA-derived small RNAs (tsRNAs). These tsRNAs exploit their linear sequences and newly arranged 3D structures for unexpected biological functions, epitomizing the tRNA "renovatio" (from Latin, meaning renewal, renovation, and rebirth). Emerging methods to uncover full tRNA/tsRNA sequences and modifications, combined with techniques to study RNA structures and to integrate AI-powered predictions, will enable comprehensive investigations of tRNA fragmentation products and new interaction potentials in relation to their biological functions. We anticipate that these directions will herald a new era for understanding biological complexity and advancing pharmaceutical engineering.
Assuntos
Aminoacil-tRNA Sintetases , RNA de Transferência , RNA de Transferência/metabolismo , Anticódon , Aminoacil-tRNA Sintetases/metabolismo , Ribossomos/metabolismo , RNA Mensageiro/genéticaRESUMO
In animals, PIWI-interacting RNAs (piRNAs) silence transposons, fight viral infections, and regulate gene expression. piRNA biogenesis concludes with 3' terminal trimming and 2'-O-methylation. Both trimming and methylation influence piRNA stability. Our biochemical data show that multiple mechanisms destabilize unmethylated mouse piRNAs, depending on whether the piRNA 5' or 3' sequence is complementary to a trigger RNA. Unlike target-directed degradation of microRNAs, complementarity-dependent destabilization of piRNAs in mice and flies is blocked by 3' terminal 2'-O-methylation and does not require base pairing to both the piRNA seed and the 3' sequence. In flies, 2'-O-methylation also protects small interfering RNAs (siRNAs) from complementarity-dependent destruction. By contrast, pre-piRNA trimming protects mouse piRNAs from a degradation pathway unaffected by trigger complementarity. In testis lysate and in vivo, internal or 3' terminal uridine- or guanine-rich tracts accelerate pre-piRNA decay. Loss of both trimming and 2'-O-methylation causes the mouse piRNA pathway to collapse, demonstrating that these modifications collaborate to stabilize piRNAs.
Assuntos
Proteínas Argonautas/metabolismo , RNA Interferente Pequeno/metabolismo , Animais , Separação Celular , Drosophila melanogaster , Feminino , Citometria de Fluxo , Expressão Gênica , Inativação Gênica , Técnicas Genéticas , Masculino , Metilação , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Processamento de Proteína Pós-Traducional , RNA de Cadeia Dupla , Espermatócitos/metabolismo , Espermatogônias/metabolismo , Testículo/metabolismoRESUMO
Epigenetic reprogramming occurs during gametogenesis as well as during embryogenesis to reset the genome for early development. In flowering plants, many heterochromatic marks are maintained in sperm, but asymmetric DNA methylation is mostly lost. Asymmetric DNA methylation is dependent on small RNA but the re-establishment of silencing in embryo is not well understood. Here we demonstrate that small RNAs direct the histone H3 lysine 9 dimethylation during Arabidopsis thaliana embryonic development, together with asymmetric DNA methylation. This de novo silencing mechanism depends on the catalytic domain of SUVH9, a Su(Var)3-9 homolog thought to be catalytically inactive.
Assuntos
Arabidopsis/genética , Arabidopsis/metabolismo , Metilação de DNA/genética , Histonas/metabolismo , RNA de Plantas/metabolismo , Sementes/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Epigênese Genética/genética , Inativação Gênica , Sementes/genéticaRESUMO
As one of the most abundant and conserved RNA species, transfer RNAs (tRNAs) are well known for their role in reading the codons on messenger RNAs and translating them into proteins. In this review, we discuss the noncanonical functions of tRNAs. These include tRNAs as precursors to novel small RNA molecules derived from tRNAs, also called tRNA-derived fragments, that are abundant across species and have diverse functions in different biological processes, including regulating protein translation, Argonaute-dependent gene silencing, and more. Furthermore, the role of tRNAs in biosynthesis and other regulatory pathways, including nutrient sensing, splicing, transcription, retroelement regulation, immune response, and apoptosis, is reviewed. Genome organization and sequence variation of tRNA genes are also discussed in light of their noncanonical functions. Lastly, we discuss the recent applications of tRNAs in genome editing and microbiome sequencing.
Assuntos
RNA de Transferência/genética , Animais , Edição de Genes/métodos , Humanos , Biossíntese de Proteínas/genética , Splicing de RNA/genética , RNA Mensageiro/genética , Transcrição Gênica/genéticaRESUMO
Small regulatory RNA (sRNAs) are key mediators of posttranscriptional gene control in bacteria. Assisted by RNA-binding proteins, a single sRNA often modulates the expression of dozens of genes, and thus sRNAs frequently adopt central roles in regulatory networks. Posttranscriptional regulation by sRNAs comes with several unique features that cannot be achieved by transcriptional regulators. However, for optimal network performance, transcriptional and posttranscriptional control mechanisms typically go hand-in-hand. This view is reflected by the ever-growing class of mixed network motifs involving sRNAs and transcription factors, which are ubiquitous in biology and whose regulatory properties we are beginning to understand. In addition, sRNA activity can be antagonized by base-pairing with sponge RNAs, adding yet another layer of complexity to these networks. In this article, we summarize the regulatory concepts underlying sRNA-mediated gene control in bacteria and discuss how sRNAs shape the output of a network, focusing on several key examples.
Assuntos
RNA Bacteriano , Pequeno RNA não Traduzido , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , Regulon , Pequeno RNA não Traduzido/genética , Pequeno RNA não Traduzido/metabolismo , Regulação Bacteriana da Expressão Gênica , Bactérias/genética , Bactérias/metabolismo , Bactérias Gram-Negativas/genética , Bactérias Gram-Negativas/metabolismoRESUMO
It has been well documented that mutations in coding DNA or cis-regulatory elements underlie natural phenotypic variation in many organisms. However, the development of sophisticated functional tools in recent years in a wide range of traditionally non-model systems have revealed many 'unusual suspects' in the molecular bases of phenotypic evolution, including upstream open reading frames (uORFs), cryptic splice sites, and small RNAs. Furthermore, large-scale genome sequencing, especially long-read sequencing, has identified a cornucopia of structural variation underlying phenotypic divergence and elucidated the composition of supergenes that control complex multi-trait polymorphisms. In this review article we highlight recent studies that demonstrate this great diversity of molecular mechanisms producing adaptive genetic variation and the panoply of evolutionary paths leading to the 'grandeur of life'.
Assuntos
Evolução Molecular , Fases de Leitura Aberta , Fenótipo , Fases de Leitura Aberta/genética , Humanos , Animais , Variação Genética/genética , MutaçãoRESUMO
The obligate anaerobic, enteric pathogen Clostridioides difficile persists in the intestinal tract by forming antibiotic-resistant endospores that contribute to relapsing and recurrent infections. Despite the importance of sporulation for C. difficile pathogenesis, environmental cues and molecular mechanisms that regulate sporulation initiation remain ill-defined. Here, by using RIL-seq to globally capture the Hfq-dependent RNA-RNA interactome, we discovered a network of small RNAs that bind to mRNAs encoding sporulation-related genes. We show that two of these small RNAs, SpoX and SpoY, regulate translation of the master regulator of sporulation, Spo0A, in an opposing manner, which ultimately leads to altered sporulation rates. Infection of antibiotic-treated mice with SpoX and SpoY deletion mutants revealed a global effect on gut colonization and intestinal sporulation. Our work uncovers an elaborate RNA-RNA interactome controlling the physiology and virulence of C. difficile and identifies a complex post-transcriptional layer in the regulation of spore formation in this important human pathogen.
Assuntos
Clostridioides difficile , Clostridioides , Animais , Humanos , Camundongos , Clostridioides/genética , Clostridioides/metabolismo , Clostridioides difficile/genética , Clostridioides difficile/metabolismo , Antibacterianos , RNA/metabolismo , Esporos Bacterianos/genética , Esporos Bacterianos/metabolismo , Proteínas de Bactérias/metabolismo , Regulação Bacteriana da Expressão GênicaRESUMO
Argonaute-bound microRNAs silence mRNA expression in a dynamic and regulated manner to control organismal development, physiology, and disease. We employed metabolic small RNA sequencing for a comprehensive view on intracellular microRNA kinetics in Drosophila. Based on absolute rate of biogenesis and decay, microRNAs rank among the fastest produced and longest-lived cellular transcripts, disposing up to 105 copies per cell at steady-state. Mature microRNAs are produced within minutes, revealing tight intracellular coupling of biogenesis that is selectively disrupted by pre-miRNA-uridylation. Control over Argonaute protein homeostasis generates a kinetic bottleneck that cooperates with non-coding RNA surveillance to ensure faithful microRNA loading. Finally, regulated small RNA decay enables the selective rapid turnover of Ago1-bound microRNAs, but not of Ago2-bound small interfering RNAs (siRNAs), reflecting key differences in the robustness of small RNA silencing pathways. Time-resolved small RNA sequencing opens new experimental avenues to deconvolute the timescales, molecular features, and regulation of small RNA silencing pathways in living cells.
Assuntos
Proteínas Argonautas/metabolismo , Proteínas de Drosophila/metabolismo , Homeostase/fisiologia , MicroRNAs/metabolismo , Análise de Sequência de RNA , Animais , Proteínas Argonautas/genética , Linhagem Celular , Proteínas de Drosophila/genética , Drosophila melanogaster , MicroRNAs/genéticaRESUMO
Despite the relevance of Argonaute proteins in RNA silencing, little is known about the structural steps of small RNA loading to form RNA-induced silencing complexes (RISCs). We report the 1.9 Å crystal structure of human Argonaute4 with guide RNA. Comparison with the previously determined apo structure of Neurospora crassa QDE2 revealed that the PIWI domain has two subdomains. Binding of guide RNA fastens the subdomains, thereby rearranging the active-site residues and increasing the affinity for TNRC6 proteins. We also identified two water pockets beneath the nucleic acid-binding channel that appeared to stabilize the mature RISC. Indeed, mutating the water-pocket residues of Argonaute2 and Argonaute4 compromised RISC assembly. Simulations predict that internal water molecules are exchangeable with the bulk solvent but always occupy specific positions at the domain interfaces. These results suggest that after guide RNA-driven conformational changes, water-mediated hydrogen-bonding networks tie together the converged domains to complete the functional RISC structure.
Assuntos
Proteínas Argonautas/química , Fatores de Iniciação em Eucariotos/química , Proteínas de Ligação a RNA/química , Complexo de Inativação Induzido por RNA/química , Animais , Cristalografia por Raios X , Células HEK293 , Humanos , Estrutura Quaternária de Proteína , Células Sf9 , SpodopteraRESUMO
PIWI-interacting RNAs (piRNAs) silence transposons in Drosophila ovaries, ensuring female fertility. Two coupled pathways generate germline piRNAs: the ping-pong cycle, in which the PIWI proteins Aubergine and Ago3 increase the abundance of pre-existing piRNAs, and the phased piRNA pathway, which generates strings of tail-to-head piRNAs, one after another. Proteins acting in the ping-pong cycle localize to nuage, whereas phased piRNA production requires Zucchini, an endonuclease on the mitochondrial surface. Here, we report that Armitage (Armi), an RNA-binding ATPase localized to both nuage and mitochondria, links the ping-pong cycle to the phased piRNA pathway. Mutations that block phased piRNA production deplete Armi from nuage. Armi ATPase mutants cannot support phased piRNA production and inappropriately bind mRNA instead of piRNA precursors. We propose that Armi shuttles between nuage and mitochondria, feeding precursor piRNAs generated by Ago3 cleavage into the Zucchini-dependent production of Aubergine- and Piwi-bound piRNAs on the mitochondrial surface.
Assuntos
Proteínas Argonautas/genética , Proteínas de Drosophila/genética , Mitocôndrias/genética , Fatores de Iniciação de Peptídeos/genética , RNA Helicases/genética , RNA Interferente Pequeno/genética , Animais , Drosophila melanogaster/genética , Endorribonucleases/genética , Feminino , Fertilidade/genética , Células Germinativas/metabolismo , Mitocôndrias/metabolismo , Mutação , Ovário/crescimento & desenvolvimento , Ovário/metabolismo , Proteínas de Ligação a RNA/genéticaRESUMO
Reproductive phasiRNAs (phased, small interfering RNAs) are broadly present in angiosperms and play crucial roles in sustaining male fertility. While the premeiotic 21-nt (nucleotides) phasiRNAs and meiotic 24-nt phasiRNA pathways have been extensively studied in maize (Zea mays) and rice (Oryza sativa), a third putative category of reproductive phasiRNAs-named premeiotic 24-nt phasiRNAs-have recently been reported in barley (Hordeum vulgare) and wheat (Triticum aestivum). To determine whether premeiotic 24-nt phasiRNAs are also present in maize and related species and begin to characterize their biogenesis and function, we performed a comparative transcriptome and degradome analysis of premeiotic and meiotic anthers from five maize inbred lines and three teosinte species/subspecies. Our data indicate that a substantial subset of the 24-nt phasiRNA loci in maize and teosinte are already highly expressed at the premeiotic phase. The premeiotic 24-nt phasiRNAs are similar to meiotic 24-nt phasiRNAs in genomic origin and dependence on DCL5 (Dicer-like 5) for biogenesis, however, premeiotic 24-nt phasiRNAs are unique in that they are likely i) not triggered by microRNAs, ii) not loaded by AGO18 proteins, and iii) not capable of mediating PHAS precursor cleavage. In addition, we also observed a group of premeiotic 24-nt phasiRNAs in rice using previously published data. Together, our results indicate that the premeiotic 24-nt phasiRNAs constitute a unique class of reproductive phasiRNAs and are present more broadly in the grass family (Poaceae) than previously known.