Genome duplication and angiosperm diversification: combining experimental and fossil evidence.

开花植物(被子植物)是最多样化和进化最晚的植物群，有25万种以上，其次是蕨类植物(蕨类植物)，约有10000种。被子植物的辐射、多样性和优势度的上升发生在很短的地质时间内。在这种辐射期间，被子植物从那里的祖先的水生/潮湿的栖息地转移到更干旱的环境中。解释这一事件背后的机制仍然是古植物学研究中尚未回答的关键问题之一。我们对现存植物基因组理解的进展表明，许多被子植物在其历史上可能经历了几次基因组复制(多倍体)。与它们的祖先相比，基因组的复制导致植物活力和适合度的增加。这一现象的一个众所周知的例子是现代农作物与它们的野生近亲相比的杂交活力。对模式植物拟南芥基因组复制事件的测年表明，这些事件之一发生在被子植物最初的辐射期间。这表明基因组大小的变化可能在推动这种多样性方面发挥了重要作用。然而，到目前为止，这一假设只用一种现存植物的基因组进行了验证，而且还没有对化石植物基因组大小的直接测量。因此，尽管这一想法很吸引人，但它仍然是投机性的。最近的研究表明，保卫细胞(叶表面控制气体交换的特殊细胞)的长度是活植物基因组大小的一个强有力的积极预测因素。树叶有很好的化石记录，从化石样本中获得保卫细胞的长度是直截了当的。这表明保卫细胞长度可以作为化石植物基因组大小的替代测量。我计划利用这种关系来检验这一假设，即基因组大小的增加伴随着早期被子植物的多样化。在这项植物化石调查的同时，还设计了一系列实验，以评估多倍体在与被子植物起源相关的大气二氧化碳浓度升高的干旱条件下生长时，对植物健康的影响。鉴于很大比例的农作物是多倍体，这项工作对更广泛的科学界具有相关性和重要性。

The flowering plants (angiosperms) are the most diverse and most recently evolved plant group with more than 250 000 species compared to second most diverse group, the ferns (pteridophytes) with ~10 000 species. The angiosperm radiation, diversification and rise to dominance occurred over a very short period of geological time. During this radiation the angiosperms to moved away from there ancestral aquatic/ moist habitat to more arid environments. Explaining the underpinng mechanisms behind this event remains one of the key unanswered questions in the palaeobotanical research. Advances in our understanding of the genome of living plants shows that many angiosperms may have undergone several episodes of genome duplication (polyploidy) during their history. Duplication of the genome leads to an increase in plant vigour and fitness, when compared to their ancestors. A well known example of this phenomenon is the hybrid vigour of modern crop plants when compared to their wild relatives. Dating of genome duplication events in the model plant Arabidopsis thaliana shows one of these events occurred during the initial angiosperms radiation. This suggests that changes in genome size may have played an important role in driving this diversification. However, to date this hypothesis has only been tested using the genome of one extant plant, furthermore no direct measure of the size of the genome of fossil plants exists. Consequently, although fascinating, this idea remains speculative. Recent work has shown the length of guard cells (specialised cell on the leaf surface that control gas exchange) are a strong positive predictor of genome size of living plants. Leaves have an excellent fossil record and obtaining the length of guard cells from fossil specimens is straight forward. This suggests that guard cell length could be used as a proxy measure of genome size on fossil plants. I plan to use this relationship to test the hypothesis that increase in genome size accompanied the diversification of the early angiosperms. A suite of experiments are designed to run along side this fossil plant investigation to assess how polyploidy impacts on plant health when grown in drought conditions at elevated atmospheric CO2 concentrations relevant to when the angiosperms originated. This work is relevance and importance to the wider scientific community given that a large proportion of crop plant are polyploids.