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News Article

Protein target suppresses citrus tree disease


Citrus greening has devastated citrus production in Florida over the last decade

A group of researchers have made progress in finding a treatment for a disease called Huanglongbing, also known as citrus greening, that has been decimating citrus trees across Florida. They identified a small protein from the Wolbachia bacterium which lives in the disease-transmitting Asian citrus psyllid (Diaphorina citri), that can move to another bacterium within these insects to block the so-called “prophage genes” that contain viral material in the second bacterium, which helps to prevent an insect immune reaction that could be harmful to both bacteria.

The researchers found that the protein could be used as a potential target to develop spray treatments that can protect trees against the psyllids as well as potentially helping the trees themselves fight off bacterial invasion, according to senior study author Professor Dean W. Gabriel, from the University of Florida. Wolbachia is a bacterium present in up to 60 percent of all insect species.

“In this case, one bacterium is doing a favour to the whole bacterial community living within the psyllid by shutting down a potential threat to survival of the insect host,” said Gabriel.

The citrus greening disease causes leave to turn a blotchy, mottled yellow colour. The fruits produced are smaller, with an unpleasant taste and the yield is significantly reduced. The disease has devastated Florida over the last 10 years and as a result, the state’s total citrus production has declined by about 60 percent within the last six years.

Researchers have been seeking a way to interrupt citrus greening. The disease is caused when psyllids carrying a bacteria called Candidatus Liberibacter feed on healthy trees and inject the bacteria into the trees phloem. It affects the tree from its roots to the shoots and has a long incubation period. “By the time disease is detected in one tree, the entire grove is thoroughly infested and much more difficult to treat,”
said Gabriel.

By conducting a series of laboratory experiments, the team noticed that the expression of proteins that help drive the spread of the Candidatus bacteria were suppressed when treated with extracts from the psyllids. Through further study, the researchers identified a fragment of the protein that was involved in part of the suppression, as encoded by the Wolbachia strain and secreted into the insect. This protein could move into the Candidatus bacteria, causing greening, fix itself to a genetic region that would normally promote prophage activity and inhibit these genes.

The research team have obtained a grant from the U.S. Department of Agriculture that enables them to grow the Candidatus Liberibacter bacterium in culture. Until now, this process has been difficult to achieve because, once removed from its host, the bacterium historically has destroyed itself. However, according to Gabriel, now that a protein target has been identified, it can be commercially produced and added to culture media, where the bacterium is more likely to grow.

Further information on the Asian Citrus Psyllid and Citrus Greening Disease is available on CABI’s open-access Invasive Species Compendium.

The Forest Science database, available to subscribers, has further information on citrus greening disease, by using the term huanglongbing yields 68 results.

Journal reference

Mukesh Jain, Laura A. Fleites, Dean W. Gabriel. A Small Wolbachia Protein Directly Represses Phage Lytic Cycle Genes in “ Candidatus Liberibacter asiaticus” within PsyllidsmSphere, 2017; 2 (3): e00171-17 DOI: 10.1128/mSphereDirect.00171-17

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 12 June 2017
  • Source
  • American Society for Microbiology
  • Subject(s)
  • Environment
  • Forest trees