Yun, D.-J. | Search bioRxiv

bioRxiv2026

The STA1-DOT2 interaction promotes nuclear speckle formation and splicing robustness in growth and heat stress responses

Pre-mRNA splicing is carried out by the spliceosome, a large and dynamic ribonucleoprotein complex. The spliceosome is known to be stored in nuclear speckles (NS), which are now recognized as active subnuclear organelles for splicing. However, it remains poorly understood how spliceosomal protein-protein interactions are functionally coupled to NS organization to maintain splicing robustness in plants. Here, we report the functional significance of a specific interaction between two U4/U6{middle dot}U5 tri-snRNP components of the spliceosome, STA1 and DOT2, in regulating NS organization, pre-mRNA splicing, and heat stress responses in Arabidopsis. We identified a missense mutation in DOT2 (a Snu66/SART1 homolog) from a genetic suppressor of the PRP6 homolog mutant sta1-1 (named S307). This mutation restored the weakened interaction between STA1 and DOT2 in the sta1-1 mutant background. Genetic, biochemical, and cell biological analyses showed that variation in the strength of the STA1-DOT2 interaction was closely associated with changes in NS formation, splicing efficiency, as well as growth and heat tolerance. Pharmacological inhibition of STA1-associated NS formation by tubercidin recapitulated sta1-1-like phenotypes and splicing defects, supporting a functional link between NS organization and splicing outcomes. In addition, heat-induced weakening of the STA1-DOT2 interaction was accompanied by reduced NS formation and increased intron retention at the transcriptome-wide level including key heat-responsive transcripts. Based on these observations, we propose that the STA1-DOT2 interaction, likely reflecting the assembly state of the U4/U6{middle dot}U5 tri-snRNP, functions as a heat-sensitive interaction node that couples spliceosome assembly to NS organization and splicing robustness under stress conditions.

plant biology↗

bioRxiv2021

A Calcium/Palmitoylation Switch Interfaces the Signaling Networks of Stress Response and Transition to Flowering

The precise timing of flowering in adverse environments is critical for plants to secure reproductive success. We report a novel mechanism controlling the time of flowering by which the palmitoylation-dependent nuclear import of protein SOS3/CBL4, a Ca2+-signaling intermediary in the plant response to salinity, results in the selective stabilization of the flowering time regulator GIGANTEA inside the nucleus under salt stress, while degradation of GIGANTEA in the cytosol releases the protein kinase SOS2 to achieve salt tolerance. S-acylation of SOS3 was critical for its nuclear localization and the promotion of flowering, but dispensable for salt tolerance. SOS3 interacted with the photoperiodic flowering components GIGANTEA and FKF1 on the CONSTANS gene promoter to sustain the transcription of CO and FT under salinity. Thus, SOS3 acts as a Ca2+- and palmitoylation-dependent molecular switch that fine-tunes flowering in a saline environment through the shared spatial separation and selective stabilization of GIGANTEA. The SOS3 protein connects two signaling networks to co-regulate stress adaptation and time of flowering. Short summaryS-acylation promoted the nuclear import of SOS3/CBL4 for the selective stabilization of the photoperiodic floral regulator GIGANTEA to fine-tune flowering time in a saline environment. Spatial separation of SOS3 acts as a molecular switch co-regulating stress adaptation and time of flowering.

plant biology↗