Accumulation dynamics of ARGONAUTE proteins during meiosis in Arabidopsis

Abstract

Meiosis is a specialized cell division that is key for reproduction and genetic diversity in sexually reproducing plants. Recently, different RNA silencing pathways have been proposed to carry a specific activity during meiosis, but the pathways involved during this process remain unclear. Here, we explored the subcellular localization of different ARGONAUTE (AGO) proteins, the main effectors of RNA silencing, during male meiosis in Arabidopsis thaliana using immunolocalizations with commercially available antibodies. We detected the presence of AGO proteins associated with posttranscriptional gene silencing (AGO1, 2, and 5) in the cytoplasm and the nucleus, while AGOs associated with transcriptional gene silencing (AGO4 and 9) localized exclusively in the nucleus. These results indicate that the localization of different AGOs correlates with their predicted roles at the transcriptional and posttranscriptional levels and provide an overview of their timing and potential role during meiosis.

The clade-specific target recognition mechanisms of plant RISCs

“…Clade 2 AGOs (AGO2, AGO3, and AGO7) also mainly induce post-transcriptional gene silencing (PTGS) in the cytoplasm (30,(36)(37)(38)(39). However, there have also been reports indicating that clade 1 and clade 2 AGOs can function in transcription activation, DNA repair, and DNA methylation in the nucleus (40)(41)(42).…”

“…The model plant, Arabidopsis thaliana, encodes ten different AGOs classified into three clades based on amino acid sequence similarity (Figure 1C) (25). AGO4, AGO6, and AGO9, which belong to clade 3 along with AGO8, known to be a pseudogene, incorporate 24-nt small interfering RNAs (siRNAs) in the cytoplasm and subsequently bind to the newly synthesized transcripts of the plant-specific RNA polymerase Pol V in the nucleus (26)(27)(28)(29)(30). These clade 3 RISCs recruit the DNA methyltransferase DOMAIN REARRANGED METHYLTRANSFERASE 2 (DRM2), promoting sequence-specific DNA methylation, a mechanism known as RNA-directed DNA methylation (RdDM), which leads to transcriptional gene silencing (TGS) (26,31).…”

“…These clade 3 RISCs recruit the DNA methyltransferase DOMAIN REARRANGED METHYLTRANSFERASE 2 (DRM2), promoting sequence-specific DNA methylation, a mechanism known as RNA-directed DNA methylation (RdDM), which leads to transcriptional gene silencing (TGS) (26, 31). In contrast, AGO1, AGO5, and AGO10, which belong to clade 1, form complexes with 20–22 nt microRNAs (miRNAs) and siRNAs to primarily carry out target RNA cleavage and translation inhibition in the cytoplasm (23, 27, 30, 32–35). Clade 2 AGOs (AGO2, AGO3, and AGO7) also mainly induce post-transcriptional gene silencing (PTGS) in the cytoplasm (30, 36–39).…”

“…In contrast, AGO1, AGO5, and AGO10, which belong to clade 1, form complexes with 20–22 nt microRNAs (miRNAs) and siRNAs to primarily carry out target RNA cleavage and translation inhibition in the cytoplasm (23, 27, 30, 32–35). Clade 2 AGOs (AGO2, AGO3, and AGO7) also mainly induce post-transcriptional gene silencing (PTGS) in the cytoplasm (30, 36–39). However, there have also been reports indicating that clade 1 and clade 2 AGOs can function in transcription activation, DNA repair, and DNA methylation in the nucleus (40–42).…”

The clade-specific target recognition mechanisms of plant RISCs

“…These clade 3 RISCs recruit the DNA methyltransferase DOMAIN REARRANGED METHYLTRANSFERASE 2 (DRM2), promoting sequence-specific DNA methylation, a mechanism known as RNA-directed DNA methylation (RdDM), which leads to transcriptional gene silencing (TGS) ( 26 , 31 ). In contrast, AGO1, AGO5 and AGO10, which belong to clade 1, form complexes with 20–22 nt microRNAs (miRNAs) and siRNAs to primarily carry out target RNA cleavage and translation inhibition in the cytoplasm ( 23 , 27 , 30 , 32–35 ). Clade 2 AGOs (AGO2, AGO3 and AGO7) also mainly induce post-transcriptional gene silencing (PTGS) in the cytoplasm ( 30 , 36–39 ).…”