HOS15 Modulates Alternative Splicing Homeostasis Under Cold Stress in Arabidopsis Thaliana

Alternative splicing (AS) is a key regulatory mechanism that enhances transcript diversity and plays a crucial role in plant stress responses. In this study, we investigate the role of HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15) in AS regulation under cold stress in Arabidopsis thaliana. RNA-seq analysis revealed that while cold stress is the primary driver of AS events, the absence of HOS15 amplifies splicing alterations, suggesting its involvement in maintaining splicing homeostasis. Differential alternative splicing (DAS) and differential transcript usage (DTU) analyses identified extensive AS events in hos15-2 mutant, particularly under cold stress. Yeast two-hybrid assays showed that HOS15 interacts with key spliceosome components, including serine/arginine-rich (SR) proteins (RS40, RS41, RSZ22a) and small nuclear ribonucleoproteins (snRNPs) (U1A, U2B), suggesting its role in modulating spliceosome function. Additionally, isoform switching analysis identified stress-responsive genes exhibiting splicing alterations independent of cold stress, reinforcing HOS15’s role beyond stress adaptation. Given its established role in chromatin remodelling, HOS15 may integrate chromatin modifications with splicing regulation, possibly influencing splice site selection via histone modifications. Our findings highlight HOS15 as a modulator of AS, ensuring splicing fidelity under normal and stress conditions. While cold stress is the dominant factor driving AS changes, HOS15 functions as a regulatory checkpoint, buffering excessive splicing alterations.