Project description:One of the major players controlling RNA decay is the cytoplasmic 5’ to 3’ exoribonuclease, which is conserved among eukaryotic organisms. In Arabidopsis, the 5’ to 3’ exoribonuclease XRN4 is involved in disease resistance, the response to ethylene, RNAi and miRNA-mediated RNA decay. Curiously, XRN4 appears to display selectivity among its substrates because certain 3’ cleavage products formed by miRNA-mediated decay, such as from ARF10 mRNA, accumulate in the xrn4 mutant, whereas others, such as from AGO1, do not. To examine the nature of this selectivity, transcripts that differentially accumulate in xrn4 were identified by combining PARE and Affymetrix arrays. Certain functional categories, such as stamen-associated proteins and hydrolases, were over-represented among transcripts decreased in xrn4, whereas transcripts encoding nuclear-encoded chloroplast-targeted proteins and nucleic acid-binding proteins were over-represented in transcripts increased in xrn4. To ascertain if RNA sequence influences the apparent XRN4 selectivity, a series of chimeric constructs were generated where the miRNA-complementary sites and different portions of the surrounding sequences from AGO1 and ARF10 were interchanged. Analysis of the resulting transgenic plants revealed that the presence of a 150 nucleotide sequence downstream of the ARF10 miRNA-complementary site conferred strong accumulation of the 3’ cleavage products in xrn4. In addition, sequence analysis of differentially accumulating transcripts led to the identification of 27 hexamer motifs that were over-represented in transcripts or miRNA-cleavage products accumulating in xrn4. Taken together, the data indicate that specific mRNA sequences, like those in ARF10, and mRNAs from select functional categories are attractive targets for XRN4-mediated decay. Mixed-stage inflorescences from Col-0 and xrn4-5 plants were harvested. Total RNA was extracted and hybridized to the ATH1 array to determine genes differentially expressed in xrn4-5 compared to Col-0. 2 replicates each.

Project description:Post-transcriptional gene silence (PTGS) is employed in plants to shut down transgenes, invading viral genes and a certain group of endogenous genes. Meanwhile, it is not clear how the risk of expansive PTGS from endogenous genes featured by transitive siRNA production is minimized. Here we demonstrate two essential components of the SKI complex in cytoplasmic 3’-5’ mRNA decay pathway, SKI2 and SKI3, function as negative regulators of transgene PTGS in Arabidopsis. The ski2 mutants manifested severe synthetic phenotypes with a 5’-3’ exoribonuclease mutant, ein5, which were substantially suppressed by the PTGS mutants, rdr6 and ago1. RDR6 is essential for the altered gene expression in ein5 ski2 on a transcriptome-wide scale. mRNA-seq approach was used to investigate the physiological relevance veiled by the myriad developmental phenotypes in Col-0 (C), ein5-1 (e), ski2-3 (s), ein5-1 ski2-3 (es), rdr6-11 (r) and rdr6-11 ein5-1 ski2-3 (res). Compared with Col-0, 4394 genes exhibited differential expression in ein5-1 ski2-3, much more than those in the ein5-1 (1138 genes) or ski2-3 (1040 genes) single mutant (2-fold cutoff, p < 0.01, FDR < 0.05), suggesting a largely disturbed transcriptome in the absence of both EIN5 and SKI2. While a small overlap was found between the differentially expressed genes in e/C and s/C comparisons, the gene lists from es/C, es/e and es/s comparisons (2-fold cutoff, p < 0.01, FDR < 0.05) largely overlapped with each other, indicating a collaborative function of EIN5 and SKI2 on a transcriptome-wide scale. The 1670 genes overlapped in the es/C, es/e and es/s comparisons included 1306 upregulated genes and 360 downregulated genes with only 4 genes as exception. 994 of the 1306 upregulated genes (76.1%) and 273 of the 360 downregulated genes (75.8%) were differentially expressed in the es/res comparison like that in es/C, es/e and es/s, indicating a substantial supression of the redundant function of EIN5 and SKI2 by RDR6. Taken together, our study brings to light a dual-safeguard system in preventing the expansive siRNA production by the 5’-3’ and 3’-5’ cytoplasmic mRNA decay pathways.

Project description:Post-transcriptional gene silence (PTGS) is employed in plants to shut down transgenes, invading viral genes and a certain group of endogenous genes. Meanwhile, it is not clear how the risk of expansive PTGS from endogenous genes featured by transitive siRNA production is minimized. Here we demonstrate two essential components of the SKI complex in cytoplasmic 3’-5’ mRNA decay pathway, SKI2 and SKI3, function as negative regulators of transgene PTGS in Arabidopsis. The ski2 mutants manifested severe synthetic phenotypes with a 5’-3’ exoribonuclease mutant, ein5, which were substantially suppressed by the PTGS mutants, rdr6 and ago1. RDR6 is essential for the altered gene expression in ein5 ski2 on a transcriptome-wide scale. mRNA-seq approach was used to investigate the physiological relevance veiled by the myriad developmental phenotypes in Col-0 (C), ein5-1 (e), ski2-3 (s), ein5-1 ski2-3 (es), rdr6-11 (r) and rdr6-11 ein5-1 ski2-3 (res). Compared with Col-0, 4394 genes exhibited differential expression in ein5-1 ski2-3, much more than those in the ein5-1 (1138 genes) or ski2-3 (1040 genes) single mutant (2-fold cutoff, p < 0.01, FDR < 0.05), suggesting a largely disturbed transcriptome in the absence of both EIN5 and SKI2. While a small overlap was found between the differentially expressed genes in e/C and s/C comparisons, the gene lists from es/C, es/e and es/s comparisons (2-fold cutoff, p < 0.01, FDR < 0.05) largely overlapped with each other, indicating a collaborative function of EIN5 and SKI2 on a transcriptome-wide scale. The 1670 genes overlapped in the es/C, es/e and es/s comparisons included 1306 upregulated genes and 360 downregulated genes with only 4 genes as exception. 994 of the 1306 upregulated genes (76.1%) and 273 of the 360 downregulated genes (75.8%) were differentially expressed in the es/res comparison like that in es/C, es/e and es/s, indicating a substantial supression of the redundant function of EIN5 and SKI2 by RDR6. Taken together, our study brings to light a dual-safeguard system in preventing the expansive siRNA production by the 5’-3’ and 3’-5’ cytoplasmic mRNA decay pathways. Examination of transcriptomes in 6 genotypes.

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A link between RNA metabolism and silencing affecting Arabidopsis development

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