United States Department of Agriculture, Forest Service, Southern Research Station, Southern Institute of Forest Genetics, Forest Tree Molecular Cytogenetics Laboratory, College Station, TX, 77843, USA.
United States Department of Agriculture, Agricultural Research Service, Thad Cochran Southern Horticultural Laboratory, 810 Hwy 26W, Poplarville, MS, 39470, USA.
Sci Rep. 2020 Aug 6;10(1):13174. doi: 10.1038/s41598-020-68697-6.
The African baobab (Adansonia digitata L.), also referred to as the "Tree of Life", is a majestic, long-lived and multipurpose tree of sub-Saharan Africa. Internationally, a growing demand for baobab products in the food, pharmaceutical and cosmetics industries has been observed. Considering this, there is a need for scientific information on the genetics and breeding of A. digitata, including cytogenetics, genetic diversity and reproductive biology. The objectives of our cytogenetic research were to determine the genome size, chromosome number, and organization of ribosomal DNA (45S and 5SrDNA) of A. digitata. Flow cytometry analysis revealed a 2C-DNA value of 3.8 ± 0.6 pg (1Cx monoploid genome size 919.1 ± 62.9 Mbp). Using our improved chromosome preparation technique, we were able to unequivocally count the chromosomes resulting in 2n = 4x = 168, a revised chromosome number for A. digitata. Fluorescent in situ hybridization (FISH) analysis revealed two massively large variants of 45S rDNA and their corresponding nucleolus organizer regions (NOR). The NOR variants were about two to four times larger than the main body of their respective chromosomes. To our knowledge, this is the first report of this phenomenon in a plant species. Furthermore, we found that FISH analysis using the Arabidopsis-type telomere repeat sequence probe clarified and confirmed the new chromosome number and characterized the 45S rDNA structural organization.
非洲猴面包树（Adansonia digitata L.），也被称为“生命之树”，是一种雄伟的、长寿的、多用途的撒哈拉以南非洲树种。国际上，食品、制药和化妆品行业对猴面包树产品的需求不断增长。有鉴于此，需要了解有关 A. digitata 的遗传学和育种的科学信息，包括细胞遗传学、遗传多样性和生殖生物学。我们的细胞遗传学研究旨在确定 A. digitata 的基因组大小、染色体数目和核糖体 DNA（45S 和 5SrDNA）的组织。流式细胞术分析显示 2C-DNA 值为 3.8±0.6 pg（1Cx 单倍体基因组大小为 919.1±62.9 Mbp）。使用我们改进的染色体制备技术，我们能够明确地计算出染色体的数量，得出 2n=4x=168，这是 A. digitata 的修正染色体数目。荧光原位杂交（FISH）分析显示了两个巨大的 45S rDNA 变体及其相应的核仁组织者区域（NOR）。NOR 变体比各自染色体的主体大两到四倍。据我们所知，这是在植物物种中首次报道这种现象。此外，我们发现使用拟南芥型端粒重复序列探针的 FISH 分析阐明并证实了新的染色体数目，并描述了 45S rDNA 结构组织。
