New Cottons “Pack a Punch” Against Fungi

Agricultural Research Service scientists are testing new cotton lines whose seed may pack a knockout punch against microbial attackers.

The plants' “punch” is a small protein called a peptide. Shown for the first time in test tube trials, leaf and seed extracts from cotton plants expressing the synthetic peptide D4E1 inhibited up to 100 percent of germinating Aspergillus flavus and other fungi within 30 minutes of exposure. The next step is to inoculate the cotton bolls with the fungus to see if D4E1 stops it from germinating on the seed, according to Thomas Cleveland, who leads ARS’ Food and Feed Safety Research Unit in New Orleans.

A. flavus, one of 25 fungi and bacteria that succumb to D4E1, is of particular interest because it can contaminate cottonseed with aflatoxin. Because it’s harmful to humans and other animals, aflatoxin threatens the marketability of cottonseed, which is processed into edible oil, a high-protein meal, and other products valued at $500-700 million annually.

Eventually, according to Cleveland, the peptides could offer a surrogate defense for cotton plants lacking sufficient resistance to microbial infection. This also could offset the need for chemical fungicides.

To engineer the cotton, ARS biologists Kanniah Rajasekaran and Jeffrey Cary first synthesized a gene for making D4E1 using a blueprint of amino acids — the building blocks of all protein — from Demegen, Inc. Dow AgroSciences LLC subsequently licensed the technology and is collaborating with ARS under a 1998 cooperative research and development agreement to develop disease resistant cottons.

The researchers used the microbe Agrobacterium tumefaciens to insert D4E1 into cotton seedling cells and developed a clump of genetically transformed callus material. From this, they regenerated 100 to 150 plants, but chose only 10 for further propagation and progeny testing.

The ARS-Dow AgroSciences LLC team is using specialized antibodies and mass spectrometry techniques to determine how much D4E1 is made by cottonseed, and pinpoint its location inside cotton cells. ARS is the U.S. Department of Agriculture's chief scientific agency.

Scientific contacts: Thomas Cleveland or Kanniah “Rajah” Rajasekaran, ARS Food and Feed Safety Research Unit, Southern Regional Research Center (SRRC), New Orleans, La., Cleveland: phone (504) 286-4200, fax (504) 286-4419, eclevela@srrc.ars.usda.gov. Rajasekaran: phone (504) 286-4482, fax (504) 286-4217, krajah@srrc.ars.usda.gov. Richard Ekstrom, Demegen, Inc., (412) 241-2150, fax (421) 241-2161, rdekstrom@demegen.com.