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Alternative polyadenylation (APA) is a widespread post-transcriptional modification method that changes the 3' ends of transcripts by altering poly(A) site usage. However, the longitudinal transcriptomic 3' end profile and its mechanism of action are poorly understood. We applied diurnal time-course poly(A) tag sequencing (PAT-seq) for Arabidopsis and identified 3284 genes that generated both rhythmic and arrhythmic transcripts. These two classes of transcripts appear to exhibit dramatic differences in expression and translation activisty. The asynchronized transcripts derived by APA are embedded with different poly(A) signals, especially for rhythmic transcripts, which contain higher AAUAAA and UGUA signal proportions. The Pol II occupancy maximum is reached upstream of rhythmic poly(A) sites, while it is present directly at arrhythmic poly(A) sites. Integrating H3K9ac and H3K4me3 time-course data analyses revealed that transcriptional activation of histone markers may be involved in the differentiation of rhythmic and arrhythmic APA transcripts. These results implicate an interplay between histone modification and RNA 3'-end processing, shedding light on the mechanism of transcription rhythm and alternative polyadenylation.

Eukaryotic histone deacetylation, critical for maintaining nucleosome structure and regulating gene expression, is mediated by histone deacetylases (HDACs). Although nucleosomes have been reported to regulate mRNA polyadenylation in humans, the role of HDACs in regulating polyadenylation has not been uncovered. Taking advantage of phenotypic studies on Arabidopsis, HDA6 (one of HDACs) was found to be a critical part of many biological processes. Here, we report that HDA6 affects mRNA polyadenylation in Arabidopsis. Poly(A) sites of up-regulated transcripts are closer to the histone acetylation peaks in hda6 compared to the wild-type Col-0. HDA6 is required for the deacetylation of histones around DNA on nucleosomes, which solely coincides with up-regulated or uniquely presented poly(A) sites in hda6. Furthermore, defective HDA6 results in an overrepresentation of the canonical poly(A) signal (AAUAAA) usage. Chromatin loci for generating AAUAAA-type transcripts have a comparatively low H3K9K14ac around poly(A) sites when compared to other noncanonical poly(A) signal–containing transcripts. These results indicate that HDA6 regulates polyadenylation in a histone deacetylation–dependent manner in Arabidopsis.

Mangrove plants adapt to coastal tidal mudflats with specially evolved viviparity seed development. However, very little is known about the genetic and molecular mechanisms of mangrove viviparity. Here, we tested a hypothesis that plant hormone abscisic acid (ABA) plays a significant role in precocious germination of viviparous Kandelia obovata seeds by exogenous applications. Through transcriptome analysis of ABA treated seeds, it was found that ABA repressed mangrove fruit growth and development, and there were thousands of genes differentially expressed. As a result, dynamics of the pathways were dramatically altered. In particular, “Plant hormone signal transduction” and “MAPK signaling pathway” were represented significantly. Among differentially expressed genes, some key genes of ABA signal transduction were induced, while ABA biosynthesis genes were repressed. Take ABI1 and ABI2, key negative regulators in ABA signal pathway, as examples, homologous alignment and a phylogenetic tree in various species showed that ABI1 and ABI2 are highly conserved among various species. The functional similarity of these genes was confirmed by transgenic work in Arabidopsis. Taken together, ABA inhibited mangrove viviparity, but mangroves developed a mechanism to prevent accidently increase of ABA in the harsh environment for maintaining viviparous reproductive strategy.

Auxin is widely involved in plant growth and development. However, the molecular mechanism on how auxin carries out this work is unclear. In particular, the effect of auxin on pre-mRNA post-transcriptional regulation is mostly unknown. By using a poly(A) tag (PAT) sequencing approach, mRNA alternative polyadenylation (APA) profiles after auxin treatment were revealed. We showed that hundreds of poly(A) site clusters (PACs) are affected by auxin at the transcriptome level, where auxin reduces PAC distribution in 5'-untranslated region (UTR), but increases in the 3'UTR. APA site usage frequencies of 42 genes were switched by auxin, suggesting that auxin affects the choice of poly(A) sites. Furthermore, poly(A) signal selection was altered after auxin treatment. For example, a mutant of poly(A) signal binding protein CPSF30 showed altered sensitivity to auxin treatment, indicating interactions between auxin and the poly(A) signal recognition machinery. We also found that auxin activity on lateral root development is likely mediated by altered expression of ARF7, ARF19 and IAA14 through poly(A) site switches. Our results shed light on the molecular mechanisms of auxin responses relative to its interactions with mRNA polyadenylation.