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Developmental Plasticity and Crop Plant Evolution
Fundamental new insights about the origin of phenotypic variation and novel traits are arising from the related fields of evolutionary developmental biology (a recent merging of evolutionary and developmental biology) and phenotypic (developmental) plasticity. This and other research is leading to a broadening of the Modern Synthesis and a revolution in our understanding of how evolution works. However, these concepts, which encompass plastic responses by organisms to perturbations in their external and internal environments through developmentally-mediated changes in gene expression have not been applied to the domestication of plants. Piperno and colleagues at STRI Klaus Winter, Irene Holst, and Owen McMillan, and Jeff Ross-Ibarra at University of California, Davis recently started an investigation of the effects of environmental change on phenotypic characteristics in maize’s wild ancestor teosinte (Zea mays ssp. parviglumis). Environmental growing chambers at the STRI are being used to re-create the atmospheric CO2 and temperature conditions that characterized those of the late-glacial and terminal Pleistocene periods, shortly before maize and other crops were taken under cultivation and domesticated (see image). Among the questions we are asking is if environmental inductions caused either by natural or human factors could have been directly responsible for some of the important phenotypic traits that separate wild and domesticated maize. These domestication traits have traditionally been considered a result of human selection during cultivation that acted on genetic mutations. Under the scenario investigated here, human influence would have begun after nature and gene expression engineered some of the phenotypic steps by re-organizing pre-existing variation early in plant development.
This research will continue for at least the next six years and will incorporate necessary molecular and other work. Gene expression studies focusing on whole transcriptome work will be carried out in Ross-Ibarra’s laboratory with new methods such as RNA-Seq to investigate whether phenotypic changes are a result of plastic responses to environmental perturbation and not to mutational changes, and to examine broader characteristics of the transcriptome-related features associated with domestication in the plants. In addition, we will carry out artificial selection studies on interesting phenotypes, in part to test a concept called genetic assimilation, which could plausibly account for the heritability of the phenotypes and ultimately their expression in all environments. This concept was advanced by some prominent scholars during the early period of the Modern Synthesis, but was shoved out of the mainstream of evolutionary thinking when population genetics began to ascend. It is envisioned that other wild progenitors of important crops may be similarly studied in this research in the future.
This research will also provide some of the first information on phenotypic and other characteristics of plants (e.g., growth rates and developmental strategies; seed size/morphology, fertility, and yield; pollen, starch, and phytolith characteristics; pollen production and fertility) in ice age environments, which world-wide contained 33% less ambient CO2 concentrations and were much cooler and drier than today’s over much of the planet. Many plants in addition to wild progenitors of domesticated species existed in these conditions for 80% of the time during the past two million years. Because future phenotypic and physiological responses by plants to environmental change will be largely effected through gene expression, results will also shed light on possible effects of future climate change.
For image description, click the letter "i" above the image.
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