Most Popular: The First Domesticated Maize

Maize was domesticated from its wild ancestor more than 8700 years ago.

Studies confirmed some time ago that maize derived from teosinte, a large wild grass that has five species growing in Mexico, Guatemala and Nicaragua. This recent discovery in Mexico's Central Balsas River Valley is the oldest biological evidence of domesticated maize.

"We went to the area where the closest relative to maize grows, looked for the earliest maize and found it," said lead researcher Anthony Ranere of Temple University.

Researchers found maize and squash phytoliths -- rigid microscopic bodies found in many plants -- in lakeside sediments, and traces of maize starch in crevices of many of the tools that were unearthed in excavated sites which dated back at least 8700 years.

From the article:

Maize was domesticated from its wild ancestor more than 8700 years according to biological evidence uncovered by researchers in the Mexico's Central Balsas River Valley. This is the earliest dated evidence -- by 1200 years -- for the presence and use of domesticated maize.


The researchers, led by Anthony Ranere of Temple University and Dolores Piperno of the Smithsonian National Museum of Natural History, reported their findings in two studies -- "The Cultural and chronological context of early Holocene maize and squash domestication in the Central Balsas River Valley, Mexcio" and "Starch grain and phytolith evidence for early ninth millennium B.P. maize from the Central Balsas River Valley, Mexico" -- being published in the PNAS Early Edition, March 24. According to Ranere, recent studies have confirmed that maize derived from teosinte, a large wild grass that has five species growing in Mexico, Guatemala and Nicaragua. The teosinte species that is closest to maize is Balsas teosinte, which is native to Mexico's Central Balsas River Valley.


"We went to the area where the closest relative to maize grows, looked for the earliest maize and found it," said Ranere. "That wasn't surprising since molecular biologists had determined that Balsas teosinte was the ancestral species to maize. So it made sense that this was where we would find the earliest domestication of maize."


The study began with Piperno, a Temple University anthropology alumna, finding evidence in the form of pollen and charcoal in lake sediments that forests were being cut down and burned in the Central Balsas River Valley to create agricultural plots by 7000 years ago. She also found maize and squash phytoliths -- rigid microscopic bodies found in many plants -- in lakeside sediments.


Ranere, an archaeologist, joined in the study to find rock shelters or caves where people lived in that region thousands of years ago. His team carried out excavations in four of the 15 caves and rock shelters visited in the region, but only one of them yielded evidence for the early domestication of maize and squash.


Ranere excavated the site and recovered numerous grinding tools. Radiocarbon dating showed that the tools dated back at least 8700 years. Although grinding tools were found beneath the 8700 year level, the researchers were not able to obtain a radiocarbon date for the earliest deposits. Previously, the earliest evidence for the cultivation of maize came from Ranere and Piperno's earlier research in Panama where maize starch and phytoliths dated back 7600 years.


Ranere said that maize starch, which is different from teosinte starch, was found in crevices of many of the tools that were unearthed.


"We found maize starch in almost every tool that we analyzed, all the way down to the bottom of our site excavations," Ranere said. "We also found phytoliths that comes from maize or corn cobs, and since teosinte doesn't have cobs, we knew we had something that had changed from its wild form."
Ranere said that their findings also supported the premise that maize was domesticated in a lowland seasonal forest context, as opposed to being domesticated in the arid highlands as many researchers had once believed.


"For a long time, I though it strange that researchers argued about the location and age of maize domestication yet never looked in the Central Balsas River Valley, the homeland for the wild ancestor," said Ranere. "Dolores was the first one to do it.'

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In Fight Against Pathogens, Calcium Helps Plants Make Their Own Aspirin

Calcium builds strong bones, good teeth - and healthy plants, according to a new study from Washington State University.

Experiments show that calcium, when bound to a protein called calmodulin, prompts plants to make salicylic acid (SA) when threatened by infection or other danger. SA is a close chemical relative of aspirin. In plants, SA acts as a signal molecule that kicks off a series of reactions that help defend against external threats.

"That plants make salicylic acid has been known for more than 100 years," said B.W. Poovaiah, Regents Professor and director of the study, "but the role of calcium in signaling a plant to make SA has not been known before."

"We are now beginning to understand the molecular mechanism connecting the calcium/calmodulin signaling to plant immunity," said Poovaiah.

The study will appear in an upcoming issue of the journal Nature and is now available online at http://dx.doi.org/10.1038/nature07612.

Poovaiah said that in controlling salicylic acid level, calcium acts like a gatekeeper within the cells of a plant, directing incoming information and helping the plant respond to such dangers as pathogen attacks. Normal, healthy plants have a low level of SA in their cells. That level rises when the plant is threatened by infection or environmental stress.

"When we expect danger, we try to take precautions," said Poovaiah. "Plants cannot run away. Plants have to turn on their built-in system to protect themselves. The plant has to produce different signal molecules. One of them is salicylic acid."

According to lead author, assistant research professor Liqun Du, SA sets off defensive measures within the plant, such as the "hypersensitive reaction" in which cells around an infection site die, forming a barrier that keeps the pathogen from invading deeper into the plant. That provides protection against the immediate threat. SA also activates the plant's systemic acquired resistance, a form of immunity that protects the plant from further pathogen attacks.

But a rise in SA levels also causes the plant to slow its growth, perhaps saving its strength for the battle against the pathogen. That sets up a challenging situation for both the plant - grow faster or protect myself better? - and farmers, who might view SA as a tool to protect their plants from disease. A plant that makes high levels of SA all the time will be safe from infection but will grow slowly. A plant that makes little or no SA will grow like gangbusters but be very susceptible to infection.

"It's a fine balance," said Du. "Too much is bad; too little is bad."

Working with the small mustard plant Arabidopsis thaliana, Poovaiah¹s research team showed that the key step in this balancing act is the interaction between calcium/calmodulin and a protein called AtSR1, which suppresses the production of salicylic acid. Stress or infection causes a spike in calcium within the plant cells, which, in combination with calmodulin, acts as a specific signal controlling the activity of AtSR1 and the formation of SA.

In an environment with few pathogens, a plant will have low levels of SA. The plant lets its guard down and devotes more resources to growth. If it becomes infected, SA production goes up, and the plant dials back its growth and puts more resources into defense.

The importance of AtSR1 was especially clear in experiments in which plants were engineered to have more or less AtSR1 than normal. Plants that have extra AtSR1 make almost no SA. They grow larger and faster than a normal plant, but easily succumb to infection. Plants that lack the gene for AtSR1 develop high levels of SA and deploy their immune responses all the time. They are nearly impervious to infection, but small in size. The same is true of plants whose AtSR1 has been changed so it cannot bind to calcium/calmodulin, demonstrating the crucial role played in this system by calcium and calmodulin.

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