Alternative 3′ UTRs contributes to post-transcriptional gene expression regulation under high salt stress

High salt stress continually challenges growth and survival of many plants, but the underlying molecular basis is not fully explored. Alternative polyadenylation (APA) produces mRNAs with different 3′UTRs (alternative 3′UTRs) to regulate gene expression at post-transcriptional level. However, the roles of such process in response to salt stress remain elusive. Here, we reported that alternative 3′UTRs responded to high salt stress in the halophyte- Spartina alterniflora , which tolerant to hash salt environment. High salt stress induced the global APA and increased the prevalence of APA events. Strikingly, high salt stress significantly led to 3′ UTR lengthening of 207 transcripts through increasing the usage of distal poly(A) sites. Transcripts with alternative 3′ UTRs were mainly enriched in salt stress related ion transporters. Alternative 3′ UTRs of SaHKT1 increased RNA stability and protein synthesis in vivo . Regulatory AU-rich elements were identified in the alternative 3′ UTRs and alternative 3′ UTRs increased protein level of SaHKT1 in an AU-rich element dependent manner. Finally, 3′ UTR lengthening might result from variations in poly(A) signals and poly(A) factors. Overall, these results suggest that APA is a potential novel high salt stress responsive mechanism by modulating mRNA 3′ UTR length. These results also reveal complex regulator roles of alternative 3′ UTRs coupling alternative polyadenylation and regulatory elements at post-transcriptional level in plants. One sentence summary Alternative 3′ UTRs acts as a potential novel mechanism in gene expression regulation of high salt tolerant genes ### Competing Interest Statement The authors have declared no competing interest.