Grupo de Desarrollo Reproductivo y Apomixis, Unidad de Genómica Avanzada, Laboratorio Nacional de Genómica para la Biodiversidad, Cinvestav, Irapuato 36821 Guanajuato, Mexico.
Grupo de Interacción Núcleo-Mitocondrial y Paleogenómica, Unidad de Genómica Avanzada, Laboratorio Nacional de Genómica para la Biodiversidad, Cinvestav, Irapuato 36821 Guanajuato, Mexico.
Proc Natl Acad Sci U S A. 2022 Apr 26;119(17):e2110245119. doi: 10.1073/pnas.2110245119. Epub 2022 Apr 18.
Efforts to understand the phenotypic transition that gave rise to maize from teosinte have mainly focused on the analysis of aerial organs, with little insights into possible domestication traits affecting the root system. Archeological excavations in San Marcos cave (Tehuacán, Mexico) yielded two well-preserved 5,300 to 4,970 calibrated y B.P. specimens (SM3 and SM11) corresponding to root stalks composed of at least five nodes with multiple nodal roots and, in case, a complete embryonic root system. To characterize in detail their architecture and anatomy, we used laser ablation tomography to reconstruct a three-dimensional segment of their nodal roots and a scutellar node, revealing exquisite preservation of the inner tissue and cell organization and providing reliable morphometric parameters for cellular characteristics of the stele and cortex. Whereas SM3 showed multiple cortical sclerenchyma typical of extant maize, the scutellar node of the SM11 embryonic root system completely lacked seminal roots, an attribute found in extant teosinte and in two specific maize mutants: root with undetectable meristem1 (rum1) and rootless concerning crown and seminal roots (rtcs). Ancient DNA sequences of SM10—a third San Marcos specimen of equivalent age to SM3 and SM11—revealed the presence of mutations in the transcribed sequence of both genes, offering the possibility for some of these mutations to be involved in the lack of seminal roots of the ancient specimens. Our results indicate that the root system of the earliest maize from Tehuacán resembled teosinte in traits important for maize drought adaptation.
为了理解从类蜀黍到玉米的表型转变，人们主要集中在对空气器官的分析上，而对可能影响根系的驯化特征则知之甚少。在圣马科斯洞穴（墨西哥特瓦坎）的考古挖掘中，出土了两个保存完好的 5300 到 4970 校准年 BP 的样本（SM3 和 SM11），它们对应着由至少五个节点组成的根干，具有多个节点根，并且在某些情况下，还具有完整的胚胎根系。为了详细描述它们的结构和解剖结构，我们使用激光烧蚀断层扫描技术重建了它们的节点根和盾状节的三维片段，揭示了内部组织和细胞结构的精美保存，并为木质部和皮层的细胞特征提供了可靠的形态计量参数。虽然 SM3 显示出多个现生玉米典型的皮质厚壁组织，但 SM11 胚胎根系的盾状节完全缺乏现生类蜀黍和两个特定的玉米突变体中的种脐根，这一属性在现生类蜀黍和根无分生组织 1（rum1）和冠和种脐无根（rtcs）的两个特定玉米突变体中都有发现。SM10 的古代 DNA 序列——与 SM3 和 SM11 年龄相当的第三个圣马科斯标本——显示了这两个基因转录序列的突变存在，这为这些突变中的一些可能参与古代标本中种脐根的缺失提供了可能性。我们的结果表明，特瓦坎最早的玉米根系在与玉米抗旱性相关的重要性状上与类蜀黍相似。
