Institute of Evolutionary Biology, Faculty of Biology, Biological and Chemical Research Centre, University of Warsaw, Żwirki i Wigury 101, 02-089 Warsaw, Poland.
Zoology and Didactics of Biology, Faculty of Mathematics and Natural Sciences, Bergische University Wuppertal, Gaussstraße 20, Wuppertal 42119, Germany.
Mol Phylogenet Evol. 2022 May;170:107441. doi: 10.1016/j.ympev.2022.107441. Epub 2022 Feb 18.
Organellar genomes often carry group II introns, which occasionally encode proteins called maturases that are important for splicing. The number of introns varies substantially among various organellar genomes, and bursts of introns have been observed in multiple eukaryotic lineages, including euglenophytes, with more than 100 introns in their plastid genomes. To examine the evolutionary diversity and history of maturases, an essential gene family among euglenophytes, we searched for their homologs in newly sequenced and published plastid genomes representing all major euglenophyte lineages. We found that maturase content in plastid genomes has a patchy distribution, with a maximum of eight of them present in Eutreptiella eupharyngea. The most basal lineages of euglenophytes, Eutreptiales, share the highest number of maturases, but the lowest number of introns. We also identified a peculiar convoluted structure of a gene located in an intron, in a gene within an intron, within yet another gene, present in some Eutreptiales. Further investigation of functional domains of identified maturases show that most of them lost at least one of the functional domains, which implies that the patchy maturase distribution is due to frequent inactivation and eventual loss over time. Finally, we identified the diversified evolutionary origin of analysed maturases, which were acquired along with the green algal plastid or horizontally transferred. These findings indicate that euglenophytes' plastid maturases have experienced a surprisingly dynamic history due to gains from diversified donors, their retention, and loss.
细胞器基因组通常携带 II 组内含子，这些内含子偶尔会编码称为剪接体成熟酶的蛋白质，对于剪接至关重要。不同细胞器基因组中的内含子数量差异很大，并且在包括眼虫类在内的多个真核生物谱系中都观察到了内含子的爆发，其质体基因组中含有超过 100 个内含子。为了研究成熟酶这一眼虫类中必不可少的基因家族的进化多样性和历史，我们在新测序和已发表的代表所有主要眼虫类谱系的质体基因组中搜索了它们的同源物。我们发现质体基因组中成熟酶的含量分布不均，在 Eutreptiella eupharyngea 中最多存在 8 个。眼虫类中最基础的类群 Eutreptiales 共享最多数量的成熟酶，但内含子数量最少。我们还在一些 Eutreptiales 中鉴定到一个位于内含子中的基因、一个内含子内的基因、另一个基因内的特殊卷曲结构。对鉴定出的成熟酶的功能结构域的进一步研究表明，它们中的大多数至少失去了一个功能结构域，这意味着成熟酶分布不均是由于频繁失活和随时间推移的最终丢失所致。最后，我们确定了分析成熟酶的多样化进化起源，它们是随着绿藻质体的获得或水平转移而获得的。这些发现表明，由于来自多样化供体的获得、保留和丢失，眼虫类的质体成熟酶经历了一个令人惊讶的动态历史。
