National Institute for Basic Biology, Okazaki, Japan.
Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyu, Okinawa, Japan.
Elife. 2021 Apr 27;10:e60176. doi: 10.7554/eLife.60176.
Some sea slugs sequester chloroplasts from algal food in their intestinal cells and photosynthesize for months. This phenomenon, kleptoplasty, poses a question of how the chloroplast retains its activity without the algal nucleus. There have been debates on the horizontal transfer of algal genes to the animal nucleus. To settle the arguments, this study reported the genome of a kleptoplastic sea slug, , and found no evidence of photosynthetic genes encoded on the nucleus. Nevertheless, it was confirmed that light illumination prolongs the life of mollusk under starvation. These data presented a paradigm that a complex adaptive trait, as typified by photosynthesis, can be transferred between eukaryotic kingdoms by a unique organelle transmission without nuclear gene transfer. Our phylogenomic analysis showed that genes for proteolysis and immunity undergo gene expansion and are up-regulated in chloroplast-enriched tissue, suggesting that these molluskan genes are involved in the phenotype acquisition without horizontal gene transfer.
有些食草软体动物会从藻类食物中摄取叶绿体，并在肠道细胞中进行光合作用长达数月。这种现象被称为盗食质体，它提出了一个问题，即叶绿体在没有藻类细胞核的情况下如何保持其活性。关于藻类基因如何横向转移到动物细胞核的争论一直存在。为了解决这些争论，本研究报道了一种盗食质体的海蛞蝓的基因组，并发现细胞核上没有编码光合作用基因的证据。然而，它被证实，光照可以延长饥饿状态下软体动物的寿命。这些数据提供了一个范例，即一个复杂的适应性特征，如光合作用，可以通过一种独特的细胞器传递，而无需核基因转移，在真核生物界之间转移。我们的系统发育基因组分析表明，与蛋白质水解和免疫相关的基因发生了基因扩张，并在富含叶绿体的组织中上调表达，这表明这些软体动物基因参与了表型的获得，而没有水平基因转移。
