Nozaki Tomonari, Shigenobu Shuji
Laboratory of Evolutionary Genomics, National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi, 444-8585, Japan.
Department of Basic Biology, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), 38 Nishigonaka, Myodaiji, Okazaki, Aichi, 444-8585, Japan.
Sci Rep. 2022 Jun 1;12(1):9111. doi: 10.1038/s41598-022-12836-8.
Aphids have evolved bacteriocytes or symbiotic host cells that harbor the obligate mutualistic bacterium Buchnera aphidicola. Because of the large cell size (approximately 100 μm in diameter) of bacteriocytes and their pivotal role in nutritional symbiosis, researchers have considered that these cells are highly polyploid and assumed that bacteriocyte polyploidy may be essential for the symbiotic relationship between the aphid and the bacterium. However, little is known about the ploidy levels and dynamics of aphid bacteriocytes. Here, we quantitatively analyzed the ploidy levels in the bacteriocytes of the pea-aphid Acyrthosiphon pisum. Image-based fluorometry revealed the hyper polyploidy of the bacteriocytes ranging from 16- to 256-ploidy throughout the lifecycle. Bacteriocytes of adult parthenogenetic viviparous females were ranged between 64 and 128C DNA levels, while those of sexual morphs (oviparous females and males) were comprised of 64C, and 32-64C cells, respectively. During post-embryonic development of viviparous females, the ploidy level of bacteriocytes increased substantially, from 16 to 32C at birth to 128-256C in actively reproducing adults. These results suggest that the ploidy levels are dynamically regulated among phenotypes and during development. Our comprehensive and quantitative data provides a foundation for future studies to understand the functional roles and biological significance of the polyploidy of insect bacteriocytes.
蚜虫进化出了含有专性共生细菌蚜虫内共生菌的含菌细胞或共生宿主细胞。由于含菌细胞的细胞体积较大（直径约100μm）且在营养共生中起关键作用，研究人员认为这些细胞是高度多倍体的，并推测含菌细胞多倍体可能对蚜虫与细菌之间的共生关系至关重要。然而，对于蚜虫含菌细胞的倍性水平和动态变化知之甚少。在此，我们定量分析了豌豆蚜豆无网长管蚜含菌细胞的倍性水平。基于图像的荧光测定法揭示了含菌细胞在整个生命周期中从16倍体到256倍体的超多倍体状态。孤雌生殖胎生雌成虫的含菌细胞DNA水平在64C和128C之间，而有性形态（卵生雌虫和雄虫）的含菌细胞分别由64C以及32C至64C的细胞组成。在胎生雌虫的胚后发育过程中，含菌细胞的倍性水平大幅增加，从出生时的16C增加到活跃繁殖成虫时的128C至256C。这些结果表明倍性水平在不同表型之间以及发育过程中受到动态调节。我们全面且定量的数据为未来研究理解昆虫含菌细胞多倍体的功能作用和生物学意义奠定了基础。
