阿拉伯芥中MOS4參與在生理時鐘調控的角色

Abstract

MOS4-Associated Complex (MAC)為阿拉伯芥中參與mRNA剪接的蛋白複合體，在植物防禦病原菌上扮演重要的角色。然而，對於MAC在植物生長發育中的作用卻鮮少有相關的研究。MOS4 (Modifier of SNC1, 4)為MAC中的核心蛋白。mos4突變體植株對於光週期不敏感，在長日照情況下相較於野生型為晚開花，在短日照情況下則為提早開花。而扮演植物生理時鐘輸出者的GIGANTEA (GI)在mos4突變體植株中的表現較野生型延緩，導致下游促進開花的激活者CONSTANS (CO)也跟著延遲了表現。最終，使得開花整合者FLOWERING LOCUS T (FT)在傍晚仍維持著低表現量。另一方面，生理時鐘之中於白天表現的調控者PSEUDO-RESPONSE REGULATORS (PRRs)也出現了延遲的現象。其中，PRR7跟PRR9更被進一步挑選來觀察選擇性剪接的現象，結果顯示兩者的選擇性剪接情形在mos4突變體植株中都有增加。總合以上結果，我們的研究指出MOS4透過調控生理時鐘基因的剪接來影響到開花時間。

MOS4 (Modifier of SNC1, 4) is the core protein of the MOS4-associated complex (MAC) involved in mRNA splicing in Arabidopsis. The function of MAC in pathogen resistance has been well studied. However, the pleotropic developmental defects in the mutants of MAC members imply that MAC may also participate in many processes of plant development. Here, we found that the mos4 knock-out mutants are insensitive to photoperiod. mos4 plants display a late flowering phenotype under long-day conditions but are early flowering under short-day conditions. The expression phase of the circadian output GIGANTEA (GI) is shifted in mos4 mutants, resulting delayed expression of the flowering activator CONSTANS (CO). Consequently, the flowering integrator FLOWERING LOCUS T (FT) maintains in a low expression level in the evening. The morning loop genes are essential for maintaining the circadian clock in plants and their expression is delayed about 3 hours in mos4 mutants. Two of the morning loop members, PSEUDO-RESPONSE REGULATORS7 (PRR7) and PRR9, were further analyzed on their alternative splicing events. The alternatively spliced transcripts of PRR7 and PRR9 are increased in mos4 mutants. Taken together, our studies indicate that MOS4 may play an essential role in flowering time control through regulating the splicing of circadian clock genes.