Reconstructing the Transcriptional Ontogeny of Maize and Sorghum Supports an Inverse Hourglass Model of Inflorescence Development

First author: Samuel Leiboff; Affiliations: University of California, Berkeley (加利福尼亚大学伯克利分校): Albany, USA

Corresponding author: Samuel Leiboff

Assembling meaningful comparisons between species is a major limitation in studying the evolution of organismal form. To understand development in maize and sorghum, closely related species with architecturally distinct inflorescences, we collected RNA-seq profiles encompassing inflorescence body-plan specification in both species. We reconstructed molecular ontogenies from 40 B73 maize tassels and 47 BTx623 sorghum panicles and separated them into transcriptional stages. To discover new markers of inflorescence development, we used random forest machine learning to determine stage by RNA-seq. We used two descriptions of transcriptional conservation to identify hourglass-like stages during inflorescence development. Despite a relatively short 12 million years since their last common ancestor, we found maize and sorghum inflorescences are most different during their hourglass-like stages of development, following an inverse-hourglass model of development. We discuss whether agricultural selection may account for the rapid divergence signatures in these species and the observed separation of evolutionary pressure and developmental reprogramming.

取得不同物种之间有意义的比较组合是研究生物形态演化的主要制约因素。为了理解两个近缘但花序结构各有特色的农作物玉米和高粱的发育，作者对两个物种分别进行了包含整个花序体轴特化过程的RNA-seq图谱构建。作者根据40个玉米B73雄穗和47个高粱BTx623花序重建了分子发生，并将他们分别划分为不同的转录阶段。为了发现新的花序发育标记，作者采用了随机森林机器学习的方法通过RNA-seq数据来划分发育阶段。作者利用两个转录保守性描述来鉴定花序发育过程中的类沙漏阶段。尽管玉米和高粱的祖先分化时间相对较短，大概在12个百万年左右，但作者发现这两个作物花序的类沙漏发育阶段明显不同，并且遵循一个“反沙漏”模型。作者进一步讨论了农作物的选择是否能够解释这两个物种之间快速的分化信号以及所观察到的演化压力和发育重编程之间的分离。

P.S. “hourglass model”，沙漏模型，指的是某个连续的发育过程中，早、晚期阶段各物种之间的差异明显， 而中期阶段物种之间差异趋同。

有关“沙漏模型”：

动物参考: Kalinka et al. (2010) Gene expression divergence recapitulates the developmental hourglass model. Nature, doi: https://doi.org/10.1038/nature09634

植物参考（胚胎发生）: Quint et al. (2012) A transcriptomic hourglass in plant embryogenesis. Nature, doi: https://doi.org/10.1038/nature11394

植物参考（后胚胎发生）: Drost et al. (2016) Post-embryonic Hourglass Patterns Mark Ontogenetic Transitions in Plant Development. Molecular Biology & Evolution, doi: https://doi.org/10.1093/molbev/msw039

有关“反沙漏模型”：

动物参考: Levin et al. (2016) The mid-developmental transition and the evolution of animal body plans. Nature, doi: https://doi.org/10.1038/nature16994

有关动、植物“沙漏模型”协同演化综述: Cridge et al. (2016) Convergent occurrence of the developmental hourglass in plant and animal embryogenesis? Annals of Botany, doi: https://doi.org/10.1093/aob/mcw024

通讯：Samuel Leiboff (https://www.linkedin.com/in/samuel-leiboff)

个人简介：2008-2010年，美国加利福尼亚大学伯克利分校，学士；2011-2016年，美国康奈尔大学，博士；20016年-至今，美国加利福尼亚大学伯克利分校，博士后。

研究方向：通过转录组学、高通量成像和发育遗传学研究农作物（玉米和高粱）如何形成功能性叶片和花序。

doi: https://doi.org/10.1016/j.cub.2019.08.044

Journal: Current Biology

Published date: October 03, 2019