Abstract
RNA polymerase III (RNAPIII) contains 17 subunits forming 4 functional domains that control the different stages of RNAPIII transcription and are dedicated to the synthesis of small RNAs such as 5S rRNA and tRNAs. Here, we identified 23 genes encoding these subunits in Arabidopsis (Arabidopsis thaliana) and further analyzed 5 subunits (NRPC2, NRPC3, NRPC8, NRPABC1, and NRPABC2) encoded by 6 genes with different expression patterns and belonging to different sub-complexes. The knockdown of these genes repressed the expression of 5S rRNA and tRNAs, causing seed developmental arrest at different stages. Among these knockdown mutants, RNA-seq analysis revealed 821 common differentially expressed genes (DEGs), significantly enriched in response to stress, abscisic acid, cytokinins, and the jasmonic acid signaling pathway. Weighted gene co-expression network analysis (WGCNA) revealed several hub genes involved in embryo development, carbohydrate metabolic and lipid metabolic processes. We identified numerous unique DEGs between the mutants belonging to pathways, including cell proliferation, ribosome biogenesis, cell death, and tRNA metabolic processes. Thus, NRPC2, NRPC3, NRPC8, NRPABC1, and NRPABC2 control seed development in Arabidopsis by influencing RNAPIII activity and, thus, hormone signaling. Reduced expression of these subunit genes causes an insufficient accumulation of the total RNAPIII, leading to the phenotypes observed following the genetic knockdown of these subunits.
Highlights
Published: 20 October 2021In Arabidopsis (Arabidopsis thaliana), seed development starts with a double fertilization event that is followed by rapid proliferation and the expansion of the endosperm
NRPC7, NRPC10, NRPC4, NRPABC3, and NRPABC5 were confirmed to participate in a protein–protein interaction with NRPC3, and NRPC8 physically interacted with NRPC6, NRPC9, NRPAC1, NRPAC2, and NRPABC2 (Figure 3A). Together these results show that NRPC2, NRPC3, NRPC8, and NRPABC2 all interact with other subunits of the RNA polymerase III (RNAPIII) complex
In 10 days after flowering (DAF) nrpc3-2 seeds, the transcript levels of 5S rRNA and 16 tRNAs were reduced by more than fivefold relative to wild-type seeds. These results indicate that NRPC2, NRPC3, NRPC8, NRPABC1, and NRPABC2 regulate the transcription of 5S rRNA and tRNAs in Arabidopsis seeds (Figure 3B)
Summary
In Arabidopsis (Arabidopsis thaliana), seed development starts with a double fertilization event that is followed by rapid proliferation and the expansion of the endosperm It ends when embryo growth takes place at the expense of the endosperm. This process is controlled by several signaling pathways, including the G-protein signaling, the IKU pathway, the mitogen-activated protein kinase signaling pathway, the ubiquitin–proteasome pathway, and the pathways involving phytohormones and transcriptional regulatory factors [1,2,3]. The enzymatic core is structurally conserved across eukaryotic RNA polymerases and contains ten subunits: NRPC1, NRPC2, NRPABC1, NRPABC2, NRPABC3, NRPABC4, NRPABC5, NRPAC1, NRPAC2, and NRPC10 [6]; RNAPIII subunits 1 (NRPC1) and
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