Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, China.
PLoS One. 2013 May 27;8(5):e64981. doi: 10.1371/journal.pone.0064981. Print 2013.
The genus Camellia, belonging to the family Theaceae, is economically important group in flowering plants. Frequent interspecific hybridization together with polyploidization has made them become taxonomically "difficult taxa". The DNA content is often used to measure genome size variation and has largely advanced our understanding of plant evolution and genome variation. The goals of this study were to investigate patterns of interspecific and intraspecific variation of DNA contents and further explore genome size evolution in a phylogenetic context of the genus.
METHODOLOGY/PRINCIPAL FINDINGS: The DNA amount in the genus was determined by using propidium iodide flow cytometry analysis for a total of 139 individual plants representing almost all sections of the two subgenera, Camellia and Thea. An improved WPB buffer was proven to be suitable for the Camellia species, which was able to counteract the negative effects of secondary metabolite and generated high-quality results with low coefficient of variation values (CV) <5%. Our results showed trivial effects on different tissues of flowers, leaves and buds as well as cytosolic compounds on the estimation of DNA amount. The DNA content of C. sinensis var. assamica was estimated to be 1C = 3.01 pg by flow cytometric analysis, which is equal to a genome size of about 2940 Mb.
Intraspecific and interspecific variations were observed in the genus Camellia, and as expected, the latter was larger than the former. Our study suggests a directional trend of increasing genome size in the genus Camellia probably owing to the frequent polyploidization events.
山茶属（Camellia），隶属于山茶科（Theaceae），是开花植物中具有重要经济价值的一个属。种间频繁的杂交和多倍化使它们成为分类上的“困难类群”。DNA 含量常用于衡量基因组大小的变化，在很大程度上促进了我们对植物进化和基因组变异的理解。本研究的目的是调查山茶属种间和种内 DNA 含量的变化模式，并进一步在系统发育背景下探讨基因组大小的进化。
方法/主要发现：使用碘化丙啶流式细胞术分析对代表两个亚属，即山茶亚属和茶亚属几乎所有组的 139 个个体植物的 DNA 量进行了测定。证明 WPB 缓冲液改良剂适合山茶属物种，可以抵消次生代谢物的负面影响，产生变异系数（CV）<5%的高质量结果。我们的结果表明，不同组织（花、叶和芽）以及细胞质化合物对 DNA 含量的估计几乎没有影响。通过流式细胞术分析，估计 assamica 型的中国茶（C.sinensis var.assamica）的 DNA 含量为 1C=3.01pg，相当于大约 2940 Mb 的基因组大小。
在山茶属中观察到种内和种间的变异，正如预期的那样，后者大于前者。我们的研究表明，山茶属的基因组大小可能存在增加的趋势，这可能是由于频繁的多倍化事件。
