Genome size variation and evolution in Dipterocarpaceae

Background: Dipterocarpaceae is a pantropical tree family that plays an important role in our understanding of the ecology of Asian tropical rain forests. However, genome sizes for members of the Dipterocarpaceae are still poorly known.
Aims: To report the genome size of 115 dipterocarp species and examine the variation and evolution of genome size in this family.
Methods: Genome size was estimated using flow cytometry. Both the rpoB and trnL intron were sequenced to uncover the evolution of genome size within a phylogenetic framework.
Results: The 1C genome size varied between 0.267 and 0.705 pg in Shorea hemsleyana and Shorea ovalis, respectively, a 2.64-fold variation across the family. Most dipterocarps are characterised by very small genomes with a mean 1C value of 0.416 pg (sd = 0.075) and five polyploids are recorded. The ancestral genome size for dipterocarps was reconstructed as 1Cx = 0.481 pg (95% CI = 0.433–0.534).
Conclusions: Genome size variation in dipterocarps was characterised by very small values with a narrow range. Overall, genome size reduction from the ancestral state is a general trend in Dipterocarpaceae.

背景：龙脑香科（Dipterocarpaceae）是一类泛热带乔木类群，对于我们认识亚洲热带雨林的生态系统具有重要意义。但目前学界对该科植物的基因组大小仍缺乏充分认知。
研究目的：本研究报道115种龙脑香科植物的基因组大小，并探究该科植物基因组大小的变异模式与演化规律。
研究方法：采用流式细胞术估算基因组大小；通过测序rpoB基因与trnL内含子序列，在系统发育框架下解析基因组大小的演化历程。
研究结果：本研究涉及的娑罗双属（Shorea）植物中，赫姆斯利娑罗双（Shorea hemsleyana）与椭圆叶娑罗双（Shorea ovalis）的1C基因组大小分别为0.267 pg与0.705 pg，龙脑香科整体的基因组大小变异幅度达2.64倍。多数龙脑香科植物拥有极小的基因组，平均1C值为0.416 pg（标准差=0.075），本研究共记录到5个多倍体类群。龙脑香科植物的祖先基因组大小经重建为1Cx=0.481 pg（95%置信区间CI=0.433–0.534）。
研究结论：龙脑香科植物的基因组大小变异以数值偏小且分布范围狭窄为典型特征。整体而言，相较于祖先基因组大小，基因组尺寸的缩减是龙脑香科的普遍演化趋势。