The nuclear exosome subunit HEN2 acts independently of the core exosome to assist transcription in Arabidopsis.

Regulation of gene expression is at the frontier of plant responses to various external stimuli including stress. RNA polymerase-based transcription and post-transcriptional degradation of RNA play vital roles in this regulation. Here, we show that HUA ENHANCER 2 (HEN2), a co-factor of the nuclear exosome complex, influences RNAPII transcription elongation in Arabidopsis (Arabidopsis thaliana) under cold conditions. Our results demonstrate that a hen2 mutant is cold sensitive and undergoes substantial transcriptional changes compared to wild type when exposed to cold conditions. We found an accumulation of 5' fragments from a subset of genes (including C-repeat binding factors 1-3 [CBF1-3]) that do not carry over to their 3' ends. In fact, hen2 mutants have lower levels of full-length mRNA for a subset of genes. This distinct 5'-end accumulation and 3'-end depletion was not observed in other NEXT complex members or core exosome mutants, highlighting HEN2's distinctive role. We further used RNAPII-associated nascent RNA to confirm that the transcriptional phenotype is a result of lower active transcription specifically at the 3' end of these genes in a hen2 mutant. Taken together, our data point to the unique role of HEN2 in maintaining RNAPII transcription dynamics especially highlighted under cold stress.