在植物中，熱應(yīng)激誘導(dǎo)選擇性剪接的變化，包括內(nèi)含子保留；這些事件可以迅速改變蛋白質(zhì)或下調(diào)蛋白質(zhì)活性，產(chǎn)生非功能性亞型或誘導(dǎo)無義介導(dǎo)的mRNA衰變。親核環(huán)素（CYPs）是多細(xì)胞真核生物剪接體復(fù)合體中的輔助蛋白。然而，植物CYPs是否參與前體mRNA剪接仍不清楚。在這里，我們發(fā)現(xiàn)擬南芥CYP18-1對于有效去除內(nèi)含子是必需的，內(nèi)含子是在萌發(fā)過程中因熱應(yīng)激而保留的。CYP18-1與第二步剪接因子（PRP18a、PRP22和SMP1）相互作用，并與熱應(yīng)激時的U2和U5小核RNA相關(guān)。CYP18-1與磷酸化PRP18a結(jié)合，CYP18-1濃度的增加與PRP18a去磷酸化的增加有關(guān)。此外，相互作用和原生質(zhì)體轉(zhuǎn)染實驗顯示，CYP18-1和PP2A型磷酸酶PP2A B??共同調(diào)節(jié)PRP18a去磷酸化。熱應(yīng)激下，qpr-RNA剪接和qprt-seqns是必需的。總的來說，我們揭示了CYP18-1激活PRP18去磷酸化的作用機(jī)制，并表明CYP18-1對于植物中保留內(nèi)含子的有效剪接和對熱應(yīng)激的快速反應(yīng)至關(guān)重要。
In plants, heat stress induces changes in alternative splicing, including intron retention; these events can rapidly alter proteins or downregulate protein activity, producing non-functional isoforms or inducing nonsense-mediated decay of mRNA. Nuclear cyclophilins (CYPs) are accessory proteins in the spliceosome complexes of multicellular eukaryotes. However, whether plant CYPs are involved in pre-mRNA splicing remains unknown. Here, we found that Arabidopsis thaliana CYP18-1 is necessary for the efficient removal of introns that are retained in response to heat stress during germination. CYP18-1 interacts with step II splicing factors (PRP18a, PRP22, and SMP1) and associates with the U2 and U5 small nuclear RNAs in response to heat stress. CYP18-1 binds to phospho-PRP18a, and increasing concentrations of CYP18-1 are associated with increasing dephosphorylation of PRP18a. Furthermore, interaction and protoplast transfection assays revealed that CYP18-1 and the PP2A-type phosphatase PP2A B?? co-regulate PRP18a dephosphorylation. RNA-seq and RT-qPCR analysis confirmed that CYP18-1 is essential for splicing introns that are retained under heat stress. Overall, we reveal the mechanism of action by which CYP18-1 activates the dephosphorylation of PRP18 and show that CYP18-1 is crucial for the efficient splicing of retained introns and rapid responses to heat stress in plants.
