The effect of 'Candidatus Liberibacter asiaticus' infection on the proteomic profiles and nutritional status of pre-symptomatic and symptomatic grapefruit (Citrus paradisi) plants

Authors: Nwugo, Chika; Lin, Hong; Duan, Ping; Civerolo, Edwin

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2013
Publication Date: 4/11/2013
Citation: Nwugo, C.C., Lin, H., Duan, Y., Civerolo, E.L. 2013. The effect of 'Candidatus Liberibacter asiaticus' infection on the proteomic profiles and nutritional status of pre-symptomatic and symptomatic grapefruit (Citrus paradisi) plants. Biomed Central (BMC) Plant Biology. Available: http://dx.doi.org/10.1186/1471-2229-13-59.

Interpretive Summary: The highly destructive citrus disease, huanglongbing (HLB), is responsible for severe economic losses to citrus production worldwide. The disease is commonly associated with the bacterium, ‘Candidatus Liberibacter asiaticus’ (Las), which is one of three presumptive causal agents all belonging to the ‘Candidatus Liberibacter spp.’ group. To better understand host plant response to HLB, two dimension polyacrylamide gel electrophoresis (2D-PAGE), mass spectrometry (MS) and inductively coupled plasma spectroscopy analyses were used to investigate protein expression profiles and nutritional status of leaves from Las-infected grapefruit plants that were pre-symptomatic or displaying symptoms of HLB. 2D-PAGE and MS analysis identified 56 proteins including those associated with photosynthesis, protein synthesis, and metabolism were down-regulated in response to Las-infection, which correlated with significant Las-mediated reductions in the concentrations of Ca, Mg, Fe, Zn, Mn, and Cu, especially in symptomatic plants. Interestingly, 13 proteins including those involved in pathogen response, redox-homeostasis and starch anabolism were up-regulated in response to Las-infection, which correlated with a Las-mediated increase in K concentration in pre-symptomatic or symptomatic plants. This study provides new information regarding the biochemical and physiological responses of citrus plants to HLB which will be useful for the development of host-based biomarker(s) for early detection and improved nutritional management of the disease.

Technical Abstract: Huanglongbing (HLB) is a highly destructive citrus disease which threatens citrus production worldwide. Among three known ‘Candidatus Liberibacter’ species associated with HLB, ‘Ca. Liberibacter asiaticus’ (Las) is the most prevalent. To better understand the physiological and molecular processes involved in host responses to Las infection, proteomic analyses via 2-DE and mass spectrometry as well as ICP spectroscopy analysis were employed to elucidate the global protein expression profiles and nutrient concentrations in leaves of grapefruit plants that were infected with Las at pre-symptomatic or symptomatic stages for HLB. A Las-mediated down-regulation of 71 protein spots that matched to 56 proteins including those associated with photosynthesis, protein synthesis, and metabolism was correlated with significant reductions in the concentrations of Ca, Mg, Fe, Zn, Mn, and Cu, especially in symptomatic plants. Interestingly, a Las-mediated up-regulation of 26 protein spots that matched to 13 proteins including those associated with pathogen response, redox-homeostasis and starch anabolism was correlated with an increase in K concentration in pre-symptomatic or symptomatic plants. Since starch synthase requires K for activation, this study is the first to highlight a coordinated accumulation of granule-bound starch synthase and K in Las-infected plants. This study describes biochemical and physiological responses of citrus plants to HLB, a key step in the development of host-based biomarker(s) for early detection and improved nutritional management of HLB.