Maize Varieties From Ancient Mexico

Sequencing of ancient corn landraces to ensure genetic diversity and resources

Maize was first domesticated in the highlands of Mexico about 10,000 years ago and is now one of the most important crop plants in the world. It is a member of the grass family, which also hosts the world's other major crops including rice, wheat, barley, sorghum, and sugar cane. As early agriculturalists selected plants with desirable traits, they were also selecting genes important for transforming a wild grass into a food plant. Since that time, Mexican farmers have created thousands of varieties suitable for cultivation in the numerous environments in the Mexican landscape—from dry, temperate highlands to moist, tropical lowlands. Because of its importance as food, the need to improve yield, and the challenges presented by changing climate, the maize genome of the B73 cultivar is being sequenced. However, because maize has a complex genome and many varieties, the genome sequence from just one variety will not be adequate to represent the diversity of maize worldwide. Mexican scientists are also sequencing and analyzing the genomes of the ancient landraces to recapture the full genetic diversity of this complex and adaptable crop.

Dr. Vielle-Calzada and his colleagues, Octavio Martinez de la Vega, Julio Vega-Arrenguin, Gustavo Hernandez-Guzman, Enrique Ibarra-Laclette, Beatriz Jimenez-Moraila, Guilermo Corona-Armenta, Cesar Alvarez-Mejia, Araceli Fernandez-Cortes, Gustavo de la Riva, Alfredo Herrera-Estrella, and Luis Herrera-Estrella, are in the process of sequencing one of the ancient popcorn races, Palomero, and analyzing its molecular and functional diversity relative to other maize races. Dr. Vielle-Calzada, of the National Laboratory of Genomics for Biodiversity, Cinvestav, Mexico, will be presenting this work at a symposium on Maize Biology at the annual meeting of the American Society of Plant Biologists in Mérida, Mexico (June 28, 11:30 AM).

Like other varieties of maize, the popcorn landraces are used throughout the world. Archeological evidence traces the earliest popcorn in the USA to New Mexico, suggesting an overland dispersal from the highlands of central Mexico into the northern plains of Mexico and then into the southwestern USA. Recent studies also support the hypothesis that popcorns are some of the oldest races of maize and group closely with teosinte in phylogenetic analyses.

Palomero is an ancient popcorn landrace of the Central and Northern Highlands Group. Vielle-Calzada and his colleagues estimated that its genome is about 22% smaller than that of B73. Their structural and functional analysis of this genome reveals a large number of unreported sequences, suggesting that the ancient landraces contain a large pool of unexplored genetic diversity that could be useful in new crop generation as well as the study of the evolution and domestication of maize and other cereals. Other studies in Mexico and elsewhere have shown that Mexican maize varieties are extraordinarily diverse.

Maize is a good model plant for studying the development of cereal crops because of its complex genome, numerous developmental mutants, and thousands of varieties. It is thought that as many as 1200 genes were selected in the process of transforming maize into a versatile food plant, and the process continues today. In regions throughout Mexico, farmers still cultivate local or criollo maize varieties in traditional ways as well as generating new varieties. They are thus contributing to conservation of the genetic diversity of maize and preserving traits that could be useful in yet unforeseen circumstances.

Many of the ancient varieties like Palomero were adaptations to different environmental conditions such as different soils, temperature, altitude, and drought. Preservation of these varieties and knowledge of their genetic and adaptive histories are of paramount importance as farmers around the world cope with changes in temperature and water availability and struggle to maintain a food supply for growing populations. These sequencing efforts are providing the data for genomic and mutant analyses that are needed for the genetic engineering of crops to improve yield as well as resistance to pests and tolerance for difficult growing conditions. The knowledge gained from these efforts can also be applied in crop and yield improvement efforts for other cereals.

Image from Velozramos

Contacts:
Dr. Jean-Philippe Vielle-Calzada
vielle@ira.cinvestav.mx
462- 623-9634
Fiesta Americana Merida : +52-999-942-1111

Brian Hyps
bhyps@aspb.org
240-354-5160
Contact: Dr. Jean-Philippe Vielle-Calzada
vielle@ira.cinvestav.mx
462-623-9634
American Society of Plant Biologists

Tags: Maize, grass family, maize genome, American Society of Plant Biologists, Palomero Maize, criollo maize

Survival Of Winged Seed, At The Age Of Global Warming.

(Kingston, ON) – The hardiest plants and those most likely to survive the climatic shifts brought about by global warming are now easier to identify, thanks to new research findings by a team from Queen's University.

"Predicting the speed at which plants are likely to migrate during climate warming could be key to ensuring their survival," says Queen's Biology professor Christopher Eckert.

Populations of plants growing at the outer edges of their natural "geographic range" exist in a precarious balance between extinction of existing populations and founding of new populations, via seed dispersal into vacant but suitable habitat. "Policy makers concerned with preserving plant species should focus not only on conserving land where species are now, but also where they may be found in the future," says Dr. Eckert.

This observation stems from his recent study – published in the scientific journal New Phytologist – which shows for the first time that natural selection gives a boost to the seed dispersal traits of those plants growing at the edges of their natural ranges.

If species are going to persist in the face of a changing climate, they must move to stay within the climate zone to which they are best adapted, Dr. Eckert explains. Their ability to relocate with shifts in regional climate brought about by global warming will largely depend on their capacity for dispersal, especially in populations near the limit of their geographical distributions.

With undergraduate student Emily Darling and PhD student Karen Samis, Dr. Eckert studied the geographic distribution and dispersal biology of Abronia umbellata (pink sand verbena), a flowering plant endemic to the Pacific coastal dunes of North America. By surveying plants throughout the 2000-km geographic range, and measuring seed dispersal with a wind tunnel in the Faculty of Applied Sciences, they showed that plants at range limits produce seeds with larger wings, thus increasing dispersal in the winds that commonly buffet costal habitats.

"The way evolution works at range limits has been brought into sharper focus by the debate over how species will respond via migration to climate warming," says Dr. Eckert. "It's clear that these marginal populations are adapted in ways that more central populations aren't."

According to Cornell University biologist Monica Geber, in an editorial focused on this new research, the Queen's team has "flipped the question of dispersal limitation on its head to ask whether range-edge populations have diverged, through adaptive evolution, from central populations to increase their colonizing ability."

There has been considerable debate as to whether these northern peripheral populations are worth conserving, Dr. Eckert notes. If they possess adaptations that will enhance their ability to expand their range during climate change, then the answer is yes, he says. His team has recently shown that in Vaccinium stamineum (deerberry) – a threatened plant related to the blueberry – the capacity for seed dispersal appears to increase sharply towards the range limit in Canada.

In addition, some threatened Canadian populations produce high-quality seeds that exhibit rapid germination and particularly high seedling growth.

"These observations are consistent with our work on coastal dune plants, suggesting that our results may have general relevance and significance for species conservation in changing global environments" says Dr. Eckert.

Contact: Nancy Dorrance
nancy.dorrance@queensu.ca
613-533-2869
Queen's University

Life on the edge: To disperse, or become extinct?

Plants existing at the edges of their natural habitats may enhance survival of the species during global warming, says Queen's professor.

Survival Of Winged Seed, At The Age Of Global Warming.

Tags: Winged Seed, Global Warming, Plant Science