The Genome-Wide Profiling of Alternative Splicing in Willow under Salt Stress

Alternative splicing (AS) is an important post-transcriptional regulatory model that can change the normal transcript expression level and possibly result in protein diversity. In this study, we conducted the full-length transcript sequencing of Salix matsudana Koidz 9901 leaves under salt treatment using the PromethION platform. A total of 4786 AS genes (9307 AS events) were determined, accounting for 7.45% of all the transcribed genes. Of them, intron retention (IR) events accounted for the most AS events (46.05%), followed by alternative 3 ' splice sites (A3SS). During salt stress, the percentage of IR events decreased, and the percentage of the others increased. Statistical results showed that 5 ' GG was the most common motif at the 5 ' end of the intron in the AS events, and GG3 ' was the most common motif at the 3 ' end. 5 ' GG-AG3 ' was the most common splice mode in the AS events. The occurrence of AS events was significantly related to the exon number, exon length, intron length, GC content, and expression abundance of the genes. During salt stress, the number of AS genes gradually increased, and they mainly participated in purine and chlorophyll metabolism, RNA transport, and autophagy. Meanwhile, the AS sites of the gene increased during salt treatment, indicating the complexity of the AS events by salt stress. A comparison of differentially expressed genes (DEGs) and differentially alternative splicing (DAS) genes during salt stress revealed that they had a different mechanism of gene expression regulation when subjected to salt stress. These results expand our knowledge of AS events and shed light on and improve our understanding of plant resistance to salt tolerance in willow.