Pathogen effectors for early detection of citrus greening disease

Authors: CANO MOGROVEJO, LILIANA - UNIVERSITY OF FLORIDA; PITINO, MARCO - UNIVERSITY OF FLORIDA; SHI, QINGCHUN; STOVER, EDDIE; Shatters, Robert - Bob

Submitted to: U.S. Patent and Trademark Office
Publication Type: Pct (patent Cooperation Treaty)
Publication Acceptance Date: 5/1/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Citrus huanglongbing (HLB), also known as citrus greening, is a devastating disease with high economic costs to the worldwide citrus industry. The disease is caused by three species of alpha-proteobacterium, “Candidatus Liberibacter asiaticus (Las),” “Ca. L. africanus,” and “Ca. L. americanus.” Las, the most widespread pathogen, is vectored by the Asian Citrus Psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae). Las attacks all species and hybrids in the Citrus genus, and upon infection, resides in the phloem of the host causing a systemic disease and can eventually kill the tree. Early infections are hard to detect because trees do not show symptoms for up to two years after infection. Also, during this early time, the bacterium is not systemically distributed within the plant so sampling for plant tissues that contain the bacterium is difficult. However, during this early infection period, the bacteria in the plant can be picked up by the insect vector and transmitted to other plants, thus spreading the disease. A potential strategy for detection, in particular early detection, of HLB in citrus would be detection of biological components (proteins, sugars, nucleic acids, and such) of the Las bacteria that are produced and secreted by the bacterium early after initial infection. Such molecules are much smaller than the bacteria and move more quickly through the plant, thus reducing the chance of sampling tissue that would not contain signs of the bacterial presence. Genes encoding small secreted proteins (identified as putative effectors) were found though data mining the published genomes of the Las bacteria. Furthermore, experiments were conducted to show that these proteins are synthesized by the bacterium during the first few days after infection. These are presented as targets for early detection using immunodetection methods routinely used in various diagnostic assays. Such early detection will allow growers to make important decisions regarding management practices for their citrus and ultimately reduce the rate of spread of the disease.

Technical Abstract: Citrus huanglongbing (HLB), also known as citrus greening, is a devastating disease with high economic costs to the worldwide citrus industry. The disease is caused by three species of alpha-proteobacterium, “Candidatus Liberibacter asiaticus (Las),” “Ca. L. africanus,” and “Ca. L. americanus.” Las, the most widespread pathogen, is vectored by the Asian Citrus Psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae). Las attacks all species and hybrids in the Citrus genus, and upon infection, resides in the phloem of the host causing a systemic disease and can eventually kill the tree. Early infections are hard to detect because trees do not show symptoms for up to two years after infection. Also, during this early time, the bacterium is not systemically distributed within the plant so sampling for plant tissues that contain the bacterium is difficult. However, during this early infection period, the bacteria in the plant can be picked up by the insect vector and transmitted to other plants, thus spreading the disease. A potential strategy for detection, in particular early detection, of HLB in citrus would be detection of biological components (proteins, sugars, nucleic acids, and such) of the Las bacteria that are produced and secreted by the bacterium early after initial infection. Such molecules are much smaller than the bacteria and move more quickly through the plant, thus reducing the chance of sampling tissue that would not contain signs of the bacterial presence. Genes encoding small secreted proteins (identified as putative effectors) were found though data mining the published genomes of the Las bacteria. Furthermore, experiments were conducted to show that these proteins are synthesized by the bacterium during the first few days after infection. These are presented as targets for early detection using immunodetection methods routinely used in various diagnostic assays. Such early detection will allow growers to make important decisions regarding management practices for their citrus and ultimately reduce the rate of spread of the disease.