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Comparative Transcriptional and Anatomical Analyses of Tolerant Rough Lemon and Susceptible Sweet Orange in Response to ‘Candidatus Liberibacter asiaticus’ Infection

November 2012 , Volume 25 , Number  11
Pages  1,396 - 1,407

Jing Fan,1,2 Chunxian Chen,2 Qibin Yu,2 Abeer Khalaf,2,3 Diann S. Achor,2 Ron H. Brlansky,2 Gloria A. Moore,3 Zheng-Guo Li,1 and Frederick G. Gmitter, Jr.2,3

1Chongqing University, College of Bioengineering, Key Laboratory of Biorheological Science and Technology, Ministry of Education, Chongqing, 400030, China; 2University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, Lake Alfred 33850, U.S.A.; 3University of Florida, Plant Molecular and Cellular Biology Program, Horticultural Sciences Department, Gainesville 32611, U.S.A.

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Accepted 10 July 2012.

Although there are no known sources of genetic resistance, some Citrus spp. are reportedly tolerant to huanglongbing (HLB), presumably caused by ‘Candidatus Liberibacter asiaticus’. Time-course transcriptional analysis of tolerant rough lemon (Citrus jambhiri) and susceptible sweet orange (C. sinensis) in response to ‘Ca. L. asiaticus’ infection showed more genes differentially expressed in HLB-affected rough lemon than sweet orange at early stages but substantially fewer at late time points, possibly a critical factor underlying differences in sensitivity to ‘Ca. L. asiaticus’. Pathway analysis revealed that stress responses were distinctively modulated in rough lemon and sweet orange. Although microscopic changes (e.g., callose deposition in sieve elements and phloem cell collapse) were found in both infected species, remarkably, phloem transport activity in midribs of source leaves in rough lemon was much less affected by HLB than in sweet orange. The difference in phloem cell transport activities is also implicated in the differential sensitivity to HLB between the two species. The results potentially lead to identification of key genes and the genetic mechanism in rough lemon to restrain disease development and maintain (or recover) phloem transport activity. These potential candidate genes may be used for improving citrus tolerance (or even resistance) to HLB by genetic engineering.

© 2012 The American Phytopathological Society