Authors

Lopez Valdivia Ivan Alden Perkins, Hannah Schneider, Miguel Vallebueno-Estrada, James Burridge, Eduardo González-Orozco, Aurora Montufar, Rafael Montiel, Jonathan Lynch, Jean-Philippe Vielle-Calzada

Source

PNAS 2022 Vol. 119 No. 17 e2110245119

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www.pnas.org with DOI number 10.1073/pnas.2110245119

Abstract

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 (Tehuacan, 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 maizemutants: root with undetectable

meristem1 (rum1) and rootless concerning crown and seminal roots (rtcs). Ancient DNA

sequences of SM10a third San Marcos specimen of equivalent age to SM3 and

SM11revealed 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 Tehuac an resembled teosinte in traits important for maize drought

adaptation.