To help develop a therapeutic treatment for citrus greening disease, a bacterial infection that threatens the future of the U.S. citrus industry, the United States Department of Agriculture Specialty Crop Research Initiative has awarded a diverse group of researchers a $10 million grant.
"We have put together a strong team of researchers from eight institutions to combat this disease. We are taking a systems approach to bring newfound knowledge from our laboratory studies to the orchard quickly and safely," said group leader Susan Brown of Kansas State.
Citrus greening disease is poised to decimate the U.S. citrus industry. The infection weakens and sometimes kills citrus trees and often causes small, unripe fruits. Though the disease has afflicted trees in Asia since the early 1900s, where it is called huanglongbing (HLB), the causative bacterium first surfaced in the U.S. in Florida in 2005. The plague has since permeated citrus groves throughout the state, where more than 70 percent of trees may be affected. Growers in Texas have already made isolated reports of infected trees.
A bacterial species called Candidatus Liberibacter asiaticus, or CLas, causes the infection and a sap-sucking insect called the Asian citrus psyllid spreads the bacterium as it feeds. Farmers have attempted to slow its advance through increased pesticide use, but this strategy has failed to stop it.
In an effort to block the transmission of CLas between trees, while curing existing infections, the researchers will use a comprehensive, multi-pronged approach that considers every gene, protein and metabolite within all three components of the problem: the bacterium, insect and citrus. Using proteomics, the study of every protein within an organism, genomics the study of all DNA in the genome, and metabolomics, the study of all metabolites, the researchers can find — and potentially block — interactions between specific molecules required to move the bacterium from tree to insect to tree.
Michelle Cilia of the Boyce Thompson Institute at Cornell University and a Research Molecular Biologist at the USDA Agricultural Research Service (ARS), along with Robert Shatters, of the USDA ARS station in Fort Pierce, Florida and Professor John Lis of Cornell University are developing targeted therapies that will kill the Asian citrus psyllid when it feeds on the plant or will block the bacterium from colonizing the psyllid when it enters the gut.
Cilia will use proteomics approaches to identify key protein interactions that occur during transmission and will test resulting therapeutic compounds in the greenhouse. "These protein or RNA molecules can be delivered from within the tree so that the psyllids get these blockers as they're feeding," said Cilia.
To handle the masses of the "omics" data that the group will generate, bioinformaticists in the laboratory of Lukas Mueller at the Boyce Thompson Institute at Cornell University are building a citrus greening portal (http://citrusgreening.org/) that will visualize connections among the proteomic, metabolomic and genomic data from the bacterium, psyllid and citrus. Mueller's group has experience building databases for individual organisms, such as cassava, but this is the first database that will link all three organisms involved in citrus greening.
The citrus greening portal will also make this data available to the public, and most importantly, to citrus growers. A vital component of the project will be reaching out to growers to give them a voice in deciding how the treatments are developed and applied. The citrus industry is deeply involved in finding a solution and has contributed large amounts of funding to support citrus greening research.
In the long-term, researchers hope to create citrus varieties that are resistant to the infection, using biotechnological approaches. USDA ARS horticulturist and geneticist Ed Stover is already working on transgenic plants that will deliver a treatment to the psyllid through the phloem—the tubes that transport nutrients to all parts of the plant—where the psyllids feed.
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