Species within the green algal order Cladophorales have an unconventional plastome structure where individual coding regions or small numbers of genes occur as linear single‐stranded DNAs folded into hairpin structures. Another group of photosynthetic organisms with an equivalently reduced chloroplast genome are the peridinin dinoflagellates of the Alveolata eukaryotic lineage whose plastomes are mini‐circles carrying one or a few genes required for photosynthesis. One unusual aspect of the Alveolata is the polyuridylylation of mRNA 3′ ends among peridinin dinoflagellates and the chromerid algae. This study was conducted to understand if an unconventional highly reduced plastome structure co‐occurs with unconventional RNA processing. To address this, the 5′ and 3′ mRNA termini of the known chloroplast genes of Pithophora roettleri (order Cladophorales) were analyzed for evidence of post‐transcriptional processing. Circular Reverse Transcriptase PCR (cRT‐PCR) followed by deep sequencing of the amplicons was used to analyze 5′ and 3′ mRNA termini. Evidence of several processing events were collected, most notably the 3′ termini of six of the eight genes were polyuridylylated, which has not been reported for any lineage outside of the Alveolata. Other processing events include poly(A) and heteropolymeric 3′ additions, 5′ primary transcript start sites, as well as the presence of circularized RNAs. Five other species representing other green algal lineages were also tested and poly(U) additions appear to be limited to the order Cladophorales. These results demonstrate that chloroplast mRNA polyuridylylation is not the sole provenance of photosynthetic alveolates and may have convergently evolved in two distinct photosynthetic lineages.

中文翻译：

---

叶绿体mRNA在绿藻Pithophora roettleri（Cladophorales）中被3'多尿苷酸化。

绿色藻类枝甲内的物种具有非常规的质体结构，其中单个编码区或少量基因作为线性单链DNA折叠成发夹结构而出现。另一组叶绿体基因组减少的光合作用生物是肺泡真核细胞系的peridinin dinoflagellates，其质体为带有一个或几个光合作用基因的微圆。肺泡的一个不寻常的方面是peridinin dinoflagellates和chromerid藻类之间的mRNA 3'末端的多尿苷酸化。进行这项研究是为了了解非常规高度还原的质体结构是否与非常规RNA加工同时发生。为了解决这个问题，已知的叶绿体基因的5'和3'mRNA末端罗氏（订单号）进行了转录后处理的证据分析。循环逆转录酶PCR（cRT-PCR），然后对扩增子进行深度测序，用于分析5'和3'mRNA末端。收集到一些加工事件的证据，最显着的是八个基因中六个基因的3'末端被多尿苷酸化，尚未见到肺泡外任何谱系的报道。其他加工事件包括poly（A）和3'杂聚合，5'初级转录起始位点以及环化RNA的存在。还测试了代表其他绿色藻类谱系的其他五个物种，并且poly（U）的添加似乎仅限于枝甲目。