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United States Department of Agriculture

Agricultural Research Service

Research Project: EMERGING DISEASES OF CITRUS, VEGETABLES, AND ORNAMENTALS

Location: Subtropical Plant Pathology Research

Title: Progress on dissecting and controlling the citrus huanglongbing complex

Authors
item Duan, Ping
item Zhou, Lijuan -
item Zhang, Muqing -
item Benyon, Lesley
item Armstrong, Cheryl
item Hoffman, Michele -
item Hao, Guixia
item Zou, Huasong -
item Doud, Melissa
item Fang, Ding -
item Morgan, John

Submitted to: International Research Conference on Huanglongbing
Publication Type: Abstract Only
Publication Acceptance Date: June 4, 2013
Publication Date: July 11, 2013
Citation: Duan, Y., Zhou, L., Zhang, M., Benyon, L.S., Armstrong, C.M., Hoffman, M., Hao, G., Zou, H., Doud, M.S., Fang, D., Morgan, J.K. 2013. Progress on dissecting and controlling the citrus huanglongbing complex. 2013 International Research Conference on Huanglongbing, February 4 - 7, 2013, Orlando, Florida.

Technical Abstract: Citrus huanglongbing (HLB) is a century-old and emerging disease that impedes citrus production worldwide. ‘Candidatus Liberibacter asiaticus’ (Las) is the globally prevalent species of HLB bacteria. Here we describe our molecular characterizations of Las, and our newly-developed control methods for citrus HLB. From a genomics standpoint, we revealed Las has a significantly reduced genome (1.26Mb) and unique features adapted to its intracellular life style. Although the genome is small, Las contains at least two prophages that make up ca. 1/16 of the entire genome. Frequent recombination and reasssortment of these prophages/phages may contribute to Las’s evolving diversity and plasticity. There are at least 9 different types of Las populations that may co-exist in a single infection, but some exist preferentially in different hosts and different geographical locations. Furthermore, different Las populations may account for titer variations, such as the extreme low titer of Las bacteria (detected by our quantitative polymerase chain reaction method) from seed-transmitted citrus and infected Murraya paniculata. From a functional genomics standpoint, we revealed Las encodes a functional ATP translocase and acts as an “energy parasite”. To modulate host energy biosyntheses and/or defense responses, Las encodes two novel autotransporter proteins that target to mitochondria. To compete for the limited zinc nutrient, Las encodes a ZuABC high affinity zinc uptake system. To avoid host defense machinery, Las encodes a functional flagellin that slowly triggers the citrus basal defense response. Although HLB is extremely difficult to control, our newly-developed thermotherapy and chemotherapy methods provide potential components of the integrated control for this devastating disease. In addition to the molecular characterization of the Las bacterium and its responses to stress, we have also revealed the dynamics of the microbial community (over 7000 OTUs-“species”) in HLB-affected citrus plants and how the microbial community responds to antibiotic treatments and seasonal variations.

Last Modified: 7/28/2014
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