Endosymbiosis of unicellular eukaryotic algae into previously nonphotosynthetic eukaryotes has established chloroplasts in several eukaryotic lineages. In addition, certain unicellular organisms in several different lineages ingest algae and utilize them as temporal chloroplasts (kleptoplasts) for weeks to months before digesting them. Among these organisms, the dinoflagellate Nusuttodinium aeruginosum ingests the cryptomonad Chroomonas sp. and enlarges the kleptoplast with the aid of the cryptomonad nucleus. To understand how the cryptomonad nucleus is remodeled in the dinoflagellate, here we examined changes in the transcriptome and ploidy of the ingested nucleus. We show that, after ingestion, genes involved in metabolism, translation, and DNA replication are upregulated while those involved in sensory systems and cell motility are downregulated. In the dinoflagellate cell, the cryptomonad nucleus undergoes polyploidization that correlates with an increase in the mRNA levels of upregulated genes. In addition, the ingested nucleus almost loses transcriptional responses to light. Because polyploidization and loss of transcriptional regulation are also known to have occurred during the establishment of endosymbiotic organelles, these changes are probably a common trend in endosymbiotic evolution. Furthermore, we show that the kleptoplast and dinoflagellate are more susceptible to high light than the free-living cryptomonad but that the ingested nucleus reduces this damage.

单细胞真核藻类与先前非光合作用的真核生物的内共生已经在几个真核谱系中建立了叶绿体。此外，几种不同谱系的某些单细胞生物会摄入藻类，并将其用作颞叶绿体（盗贼质体），持续数周至数月，然后再消化它们。在这些生物体中，甲藻Nusuttodinium aeruginosum摄入隐单胞菌Chroomonas sp。并在隐单胞核的帮助下扩大盗贼体。为了了解隐藻核在甲藻中如何重塑，我们在这里检查了摄入核的转录组和倍性的变化。我们发现，摄入后，涉及代谢、翻译和 DNA 复制的基因上调，而涉及感觉系统和细胞运动的基因下调。在甲藻细胞中，隐藻核经历多倍化，这与上调基因 mRNA 水平的增加相关。此外，被摄入的细胞核几乎失去了对光的转录反应。由于在内共生细胞器建立过程中也发生了多倍化和转录调控的丧失，因此这些变化可能是内共生进化的共同趋势。此外，我们发现窃贼体和甲藻比自由生活的隐单胞菌更容易受到强光的影响，但摄入的细胞核会减少这种损害。