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Article|01 Jun 2018|OPEN
Molecular mechanisms underlying heat or tetracycline treatments for citrus HLB control
Fang Ding1,2, Victoria Allen2, Weiqi Luo2,3, Shouan Zhang4 & Yongping Duan2,
1Hubei Key Laboratory of PLant Pathology, Huazhong Agricultural University, 430070 Wuhan, Hubei, P.R. China
2USDA-ARS-USHRL, Fort Pierce, FL 34945, USA
3Center for Integrated Pest Management, North Carolina State University, Raleigh, NC 27606, USA
4IFAS-TREC, University of Florida, Homestead, FL 33031, USA

Horticulture Research 5,
Article number: 30 (2018)
doi: 10.1038/hortres.2018.30
Views: 635

Received: 30 Nov 2017
Revised: 06 Mar 2018
Accepted: 27 Mar 2018
Published online: 01 Jun 2018

Abstract

Huanglongbing (HLB), a destructive plant bacterial disease, severely impedes worldwide citrus production. In our previous reports, we revealed the molecular mechanisms of host plant responses that underlie thermotherapy against HLB. In this study, we investigated the molecular mechanism underlying heat or tetracycline treatments on the HLB bacterium, ‘Candidatus Liberibacter asiaticus’ (Las) by focusing on Las prophage/phage conversion under stress conditions. By comparing the prophage FP1 and FP2 copy number to the copy number of 16S rDNA in HLB-affected plants, we found that the relative copy number of both FP1 and FP2 increased significantly, ranging from 3.4- to 6.7-fold change when Las-infected samples underwent a temperature shift from 23 to 37, 42 or 45 °C. When treated with tetracycline at 50–150 and 200–250 µg/ml, respectively, the relative copy number of both FP1 and FP2 increased by 3.4- to 6.0-fold. In addition, analyses of Las prophage structural gene and antirepressor gene copy numbers showed similar trends for all treatments. Furthermore, transmission electron microscopy provided direct evidence of lysogenic to lytic conversion upon temperature increase. These results not only provide new insight into the molecular mechanisms underlying heat or tetracycline treatment but also suggest a novel HLB control strategy by enhancing the endogenous conversion from Las prophages to phages.