RNA SPLICING FACTOR1 (SF1) is responsible for recognizing the branch point site (BPS) sequence in introns and is critical for pre-mRNA splicing. In Arabidopsis (Arabidopsis thaliana), splicing factor1 (AtSF1) has been shown to retain the conserved function, but it is unexpected that null atsf1 mutants are viable. Here, we identified an allele of atsf1, named suppressor of thf1-4 (sot4), from suppressor screening for leaf variegation of thylakoid formation1. The sot4 mutant resulting from the G-to-R mutation at the highly conserved 198th amino acid residue within the functionally unknown domain exhibits leaf virescence associated with less accumulation of mature plastid ribosomal RNA, particularly under cold stress. Interestingly, the same point mutation in yeast Saccharomyces cerevisiae MUD synthetic-lethal 5p (SF1/Msl5p) also causes hypersensitivity to coldness and a low splicing activity for the introns with suboptimal BPS sequences. Transcriptomic profiling and reverse-transcription quantitative PCR analyses showed that expression of many genes were up- or downregulated in atsf1 via insufficient intron splicing. Our search for a BPS consensus from the retained introns in atsf1 transcriptomes, combined with RNA electrophoresis mobility shift assays, revealed that AtSF1 directly binds to the BPS consensus containing 5'-CU(U/A)AU-3'. Taken together, our data provide insight into a role for AtSF1 in regulating intron splicing efficiency, which helps plants acclimate to coldness.

RNA 剪接因子 1 (SF1) 负责识别内含子中的分支点位点 (BPS) 序列，对于前 mRNA 剪接至关重要。在拟南芥 ( Arabidopsis thaliana ) 中，剪接因子 1 (AtSF1) 已被证明保留了保守功能，但令人意外的是，无效的atsf1突变体也能存活。在这里，我们通过类囊体形成叶片杂色的抑制子筛选，鉴定了一个atsf1等位基因，称为thf1-4 抑制子( sot4 )。由功能未知结构域内高度保守的第 198 个氨基酸残基处的 G-to-R 突变产生的sot4突变体表现出与成熟质体核糖体 RNA 积累较少相关的叶绿化，特别是在冷胁迫下。有趣的是，酿酒酵母MUD 合成致死 5p (SF1/Msl5p) 中的相同点突变也会导致对寒冷的过敏以及具有次优 BPS 序列的内含子的低剪接活性。转录组分析和逆转录定量 PCR 分析表明， atsf1中许多基因的表达因内含子剪接不足而上调或下调。我们从atsf1转录组中保留的内含子中寻找 BPS 共有序列，并结合 RNA 电泳迁移率变动分析，结果表明 AtSF1 直接与包含 5'-CU(U/A)AU-3' 的 BPS 共有序列结合。总而言之，我们的数据深入了解了 AtSF1 在调节内含子剪接效率中的作用，这有助于植物适应寒冷。