The heterodimeric complex SPT4/SPT5 is a transcript elongation factor (TEF) that directly interacts with RNA polymerase II (RNAPII) to regulate messenger RNA synthesis in the chromatin context. We provide biochemical evidence that in Arabidopsis, SPT4 occurs in a complex with SPT5, demonstrating that the SPT4/SPT5 complex is conserved in plants. Each subunit is encoded by two genes SPT4-1/2 and SPT5-1/2. A mutant affected in the tissue-specifically expressed SPT5-1 is viable, whereas inactivation of the generally expressed SPT5-2 is homozygous lethal. RNAi-mediated downregulation of SPT4 decreases cell proliferation and causes growth reduction and developmental defects. These plants display especially auxin signalling phenotypes. Consistently, auxin-related genes, most strikingly AUX/IAA genes, are downregulated in SPT4–RNAi plants that exhibit an enhanced auxin response. In Arabidopsis nuclei, SPT5 clearly localizes to the transcriptionally active euchromatin, and essentially co-localizes with transcribing RNAPII. Typical for TEFs, SPT5 is found over the entire transcription unit of RNAPII-transcribed genes. In SPT4–RNAi plants, elevated levels of RNAPII and SPT5 are detected within transcribed regions (including those of downregulated genes), indicating transcript elongation defects in these plants. Therefore, SPT4/SPT5 acts as a TEF in Arabidopsis, regulating transcription during the elongation stage with particular impact on the expression of certain auxin-related genes.

3 ABSTRACT 49The regulated transport of mRNAs from the cell nucleus to the cytosol is a critical step 50 linking transcript synthesis and processing with translation. However, in plants, only few of 51 the factors that act in the mRNA export pathway have been functionally characterised. 52Flowering plant genomes encode several members of the ALY protein family, which function 53 as mRNA export factors in other organisms. Arabidopsis thaliana ALY1-4 are commonly 54 detected in root and leaf cells, but are differentially expressed in reproductive tissue. 55Moreover, the subnuclear distribution of ALY1/2 differs from that of ALY3/4. ALY1 binds 56 with higher affinity to ssRNA than dsRNA and ssDNA, and interacts preferentially with 5- THO rather than that of yeast (Yelina et al. 2010). Likewise, THO associates with UAP56, 99ALYs and MOS11 (the orthologue of CIP29) in Arabidopsis cells (Sørensen et al. 2017 (Germain et al. 2010;Lu et al. 2010;Pan et al. 2012;Xu et al. 2015; 114 Sørensen et al. 2017), but so far none of the ALY mRNA export adaptor candidates have been 115shown to function in nucleo-cytosolic transport of mRNAs in plants. 116In this study, we have systematically studied the Arabidopsis ALY proteins including their RESULTS 126 ALY proteins in Arabidopsis and other plants 127First, we compared the amino acid sequences of the four Arabidopsis ALY proteins (ALY1- sequence identity) as well as ALY3 and ALY4 (70% amino acid sequence identity) share a 137 high degree of sequence similarity, whereas the similarity of ALY1/2 versus ALY3/4 is 138 clearly lower (<42% amino acid sequence identity) (Supplemental Fig. S1B (Fig. 1A). ALY1 and truncated versions of the protein were expressed in 157 E. coli as 6xHis-GB1 fusion proteins, purified by two-step chromatography, and examined by 158 SDS-PAGE (Fig. 1B). For comparison we also used the unfused 6xHis-GB1 tag. The purified (Fig. 1C, Student's t-test, P < 0.05 and P < 0.001, respectively). The unfused 6xHis-GB1 165 tag did not exhibit affinity for ssRNA. To examine which domains of ALY1 contribute to the 166 RNA interactions, the binding to ssRNA of the different recombinant ALY1 versions was 167 measured (Fig. 1D (Fig. 3C, D). Therefore, the four ALY proteins and UAP56 228 are widely expressed in sporophytic cells of Arabidopsis plants. 229The subnuclear localisation of the ALY-GFP fusions was inspected in more detail by 230 CLSM in comparison to the UAP56-GFP and GFP-NLS controls. GFP-NLS (Antosch et al. immunofluorescence microscopy analysis (Kammel et al. 2013 (Table S1). In leaf cells, the nucleoplasmic distribution of 238 the ALY proteins appeared more heterogeneous than in root cells particularly for ALY4 that 239 partially localised to nucleoplasmic foci (Fig. 4B). Notably, the nucleolar enrichment of 253In view of the apparently ubiquitous expression of the four ALY-GFP proteins in 254 sporophytic cells, their occurrence was analysed in male and female gametophytes by CLSM. 255In mature pollen grains (Fig. 5A), the fluorescent signal of ALY1-...

We identify proteins that associate with the THO core complex, and show that the TEX1 and MOS11 components functionally interact, affecting mRNA export and splicing as well as plant development. TREX (TRanscription-EXport) is a multiprotein complex that plays a central role in the coordination of synthesis, processing and nuclear export of mRNAs. Using targeted proteomics, we identified proteins that associate with the THO core complex of Arabidopsis TREX. In addition to the RNA helicase UAP56 and the mRNA export factors ALY2-4 and MOS11 we detected interactions with the mRNA export complex TREX-2 and multiple spliceosomal components. Plants defective in the THO component TEX1 or in the mRNA export factor MOS11 (orthologue of human CIP29) are mildly affected. However, tex1 mos11 double-mutant plants show marked defects in vegetative and reproductive development. In tex1 plants, the levels of tasiRNAs are reduced, while miR173 levels are decreased in mos11 mutants. In nuclei of mos11 cells increased mRNA accumulation was observed, while no mRNA export defect was detected with tex1 cells. Nevertheless, in tex1 mos11 double-mutants, the mRNA export defect was clearly enhanced relative to mos11. The subnuclear distribution of TEX1 substantially overlaps with that of splicing-related SR proteins and in tex1 plants the ratio of certain alternative splicing events is altered. Our results demonstrate that Arabidopsis TEX1 and MOS11 are involved in distinct steps of the biogenesis of mRNAs and small RNAs, and that they interact regarding some aspects, but act independently in others.

The DEAD-box protein UAP56 (U2AF65-associcated protein) is an RNA helicase that in yeast and metazoa is critically involved in mRNA splicing and export. In Arabidopsis, two adjacent genes code for an identical UAP56 protein, and both genes are expressed. In case one of the genes is inactivated by a T-DNA insertion, wild type transcript level is maintained by the other intact gene. In contrast to other organisms that are severely affected by elevated UAP56 levels, Arabidopsis plants that overexpress UAP56 have wild type appearance. UAP56 localises predominantly to euchromatic regions of Arabidopsis nuclei, and associates with genes transcribed by RNA polymerase II independently from the presence of introns, while it is not detected at non-transcribed loci. Biochemical characterisation revealed that in addition to ssRNA and dsRNA, UAP56 interacts with dsDNA, but not with ssDNA. Moreover, the enzyme displays ATPase activity that is stimulated by RNA and dsDNA and it has ATP-dependent RNA helicase activity unwinding dsRNA, whereas it does not unwind dsDNA. Protein interaction studies showed that UAP56 directly interacts with the mRNA export factors ALY2 and MOS11, suggesting that it is involved in mRNA export from plant cell nuclei.

In eukaryotes, the regulated transport of mRNAs from the nucleus to the cytosol through nuclear pore complexes represents an important step in the expression of protein-coding genes. In plants, the mechanism of nucleocytosolic mRNA transport and the factors involved are poorly understood. The Arabidopsis (Arabidopsis thaliana) genome encodes two likely orthologs of UAP56interacting factor, which acts as mRNA export factor in mammalian cells. In yeast and plant cells, both proteins interact directly with the mRNA export-related RNA helicase UAP56 and the interaction was mediated by an N-terminal UAP56-binding motif. Accordingly, the two proteins were termed UAP56-INTERACTING EXPORT FACTOR1 and 2 (UIEF1/2). Despite lacking a known RNA-binding motif, recombinant UIEF1 interacted with RNA, and the C-terminal part of UIEF1 mainly contributed to the RNA interaction. Mutation of UIEF1, UIEF2, or both in the double-mutant 2xuief caused modest growth defects. A cross between the 2xuief and 4xaly (defective in the four ALY1-4 mRNA export factors) mutants produced the sextuple mutant 4xaly 2xuief, which displayed more severe growth impairment than the 4xaly plants. Developmental defects including delayed bolting and reduced seed set were observed in the 4xaly but not the 2xuief plants. Analysis of the cellular distribution of polyadenylated mRNAs revealed more pronounced nuclear mRNA accumulation in 4xaly 2xuief than in 2xuief and 4xaly cells. In conclusion, the results indicate that UIEF1 and UIEF2 act as mRNA export factors in plants and that they cooperate with ALY1-ALY4 to mediate efficient nucleocytosolic mRNA transport.

Formalin-fixed, paraffin-embedded (FFPE) patient tissue samples stored globally in pathology archives represent an invaluable biobank for clinical research. Unfortunately, nucleic acids isolated from FFPE tissues tend to be fragmented and chemically modified, interfering with many classical molecular analyses. Since massively parallel sequencing (MPS) technologies rely on randomly fragmented nucleic acids, we have focused a systematic study on the potential use of FFPE samples in MPS-based clinical studies. Available FFPE extraction kits were evaluated with respect to purification of RNA and DNA from different tissue types. Although the quality of the extracted nucleic acids was found to be highly dependent on the purification method used, it was possible to isolate high molecular DNA and RNA from recent FFPE specimen (fixed within one year). Extracted DNA and RNA from matching cryopreserved and FFPE specimens were successfully used for the preparation of targeted genomic (Exome-Seq) and whole transcriptome (RNA-Seq) sequencing libraries. Illumina's TruSeq exome preparation protocol was used for the preparation of Exome-Seq libraries and sequence analysis revealed that between 95.0 and 98.8 % of the reads mapped to the human genome with mismatch rates from 0.29 to 0.78 %. The preparation of RNA-Seq libraries from FFPE RNA using classical methods based on poly(dA) selection combined with oligo(dT) and random priming of cDNA synthesis is problematic due to the RNA degradation and results in 3′ biases and uneven sequence coverage. In this study, multiplexed RNA-Seq libraries were prepared using the ScriptSeq kit in combination with Ribo-Zero technology (both from Epicentre). In brief, ribosomal RNA was depleted from fragmented total RNA using Ribo-Zero followed by tagged random primed cDNA synthesis, terminal tagged second-strand synthesis, multiplexed amplification and purification. This approach results in strand-specific and paired-end sequences of coding and non-coding RNA. Sequence analysis of RNA-Seq libraries prepared from RNA isolated from a human lung tumor revealed that 96 - 98 % of the reads could be mapped and that the directional protocol worked correctly for at least 99 % of the reads. Surprisingly, more than half of the mapped reads were found to be non-human, mapping primarily to bacterial rRNA. As bacterial contamination is a potential issue in many tissue samples, we are presently testing improved versions of Ribo-Zero, including probes to bacterial rRNA. These results will, together with results from applying MPS to older matched FFPE and cryopreserved specimens, be presented at the AACR meeting. This preliminary work demonstrates the potential application of MPS to study FFPE samples. The results are promising regarding the possible use of the concealed information of archived FFPE specimens for large scale retrospective MPS-based genomic studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3181. doi:1538-7445.AM2012-3181