The transcription and export complex THO/TREX contributes to transcription termination in plants

Abstract

<jats:title>Abstract</jats:title><jats:p>Transcription termination has important regulatory functions, impacting mRNA stability, localization and translation potential. Failure to appropriately terminate transcription can also lead to read-through transcription and the synthesis of antisense RNAs which can have profound impact on gene expression. The Transcription-Export (THO/TREX) protein complex plays an important role in coupling transcription with splicing and export of mRNA. However, little is known about the role of the THO/TREX complex in the control of transcription termination. In this work, we show that two proteins of the THO/TREX complex, namely TREX COMPONENT 1 (TEX1 or THO3) and HYPER RECOMBINATION1 (HPR1 or THO1) contribute to the correct transcription termination at several loci in <jats:italic>Arabidopsis thaliana</jats:italic>. We first demonstrate this by showing defective termination in <jats:italic>tex1</jats:italic> and <jats:italic>hpr1</jats:italic> mutants at the nopaline synthase (NOS) terminator present in a T-DNA inserted between exon 1 and 3 of the <jats:italic>PHO1</jats:italic> locus in the <jats:italic>pho1-7</jats:italic> mutant. Read-through transcription beyond the NOS terminator and splicing-out of the T-DNA resulted in the generation of a near full-length <jats:italic>PHO1</jats:italic> mRNA (minus exon 2) in the <jats:italic>tex1 pho1-7</jats:italic> and <jats:italic>hpr1 pho1-7</jats:italic> double mutants, with enhanced production of a truncated PHO1 protein that retained phosphate export activity. Consequently, the strong reduction of shoot growth associated with the severe phosphate deficiency of the <jats:italic>pho1-7</jats:italic> mutant was alleviated in the <jats:italic>tex1 pho1-7</jats:italic> and <jats:italic>hpr1 pho1-7</jats:italic> double mutants. Additionally, we show that RNA termination defects in <jats:italic>tex1</jats:italic> and <jats:italic>hpr1</jats:italic> mutants leads to 3’UTR extensions in several plant genes. These results demonstrate that THO/TREX complex contributes to the regulation of transcription termination.</jats:p><jats:sec><jats:title>Author summary</jats:title><jats:p>Production of messenger RNAs (mRNAs) involves numerous steps including initiation of transcription, elongation, splicing, termination, as well as export out of the nucleus. All these steps are highly coordinated and failure in any steps has a profound impact on the level and identity of mRNAs produced. The THO/TREX protein complex is associated with nascent RNAs and contributes to several mRNA biogenesis steps, including splicing and export. However, the contribution of the THO/TREX complex to mRNA termination was poorly defined. We have identified a role for two components of the THO/TREX complex, namely the proteins TEX1 and HPR1, in the control of transcription termination in the plant <jats:italic>Arabidopsis thaliana</jats:italic>. We show that the <jats:italic>tex1</jats:italic> and <jats:italic>hpr1</jats:italic> mutants have defects in terminating mRNA at the nopaline synthase (NOS) terminator found in T-DNA insertion mutants leading to the transcriptional read-through pass the NOS terminator. We also show that <jats:italic>tex1</jats:italic> and <jats:italic>hpr1</jats:italic> mutants have defects in mRNA termination at several endogenous genes, leading to the production of 3’UTR extensions. Together, these results highlight a role for the THO/TREX complex in mRNA termination.</jats:p></jats:sec>