Alternative Polyadenylation in response to temperature stress contributes to gene regulation in Populus trichocarpa

Genome-wide change of polyadenylation (polyA) sites (also known as alternative polyadenylation, APA) is emerging as an important strategy of gene regulation in response to stress in plants. But little is known in woody perennials that are persistently dealing with multiple abiotic stresses.

Here, we performed a genome-wide profiling of polyadenylation sites under heat and cold treatments in Populus trichocarpa. Through a comprehensive analysis of polyA tail sequences, we identified 25,919 polyA-site clusters (PACs), and revealed 3429 and 3139 genes shifted polyA sites under heat and cold stresses respectively. We found that a small proportion of genes possessed APA that affected the open reading frames; and some shifts were commonly identified. Functional analysis of genes displaying shifted polyA tails suggested that pathways related to RNA metabolism were linked to regulate the APA events under both heat and cold stresses. Interestingly, we found that the heat stress induced a significantly more antisense PACs comparing to cold and control conditions. Furthermore, we showed that a unique cis-element (AAAAAA) was predominately enriched downstream of PACs in P. trichocarpa genes; and this sequence signal was only absent in shifted PACs under the heat condition, indicating a distinct APA mechanism responsive to heat tolerance.

This work provides a comprehensive picture of global polyadenylation patterns in response to temperatures stresses in trees. We show that the frequent change of polyA tail is a potential mechanism of gene regulation responsive to stress, which are associated with distinctive sequence signatures.