Proteomics analysis reveals novel host molecular mechanisms associated with thermotherapy of ‘Ca. Liberibacter asiaticus’-infected citrus plants

Abstract

BackgroundCitrus Huanglongbing (HLB), which is linked to the bacterial pathogen ‘Ca. Liberibacter asiaticus’ (Las), is the most devastating disease of citrus plants, and longer-term control measures via breeding or genetic engineering have been unwieldy because all cultivated citrus species are susceptible to the disease. However, the degree of susceptibility varies among citrus species, which has prompted efforts to identify potential Las resistance/tolerance-related genes in citrus plants for application in breeding or genetic engineering programs. Plant exposure to one form of stress has been shown to serendipitously induce innate resistance to other forms of stress and a recent study showed that continuous heat treatment (40 to 42 °C) reduced Las titer and HLB-associated symptoms in citrus seedlings. The goal of the present study was to apply comparative proteomics analysis via 2-DE and mass spectrometry to elucidate the molecular processes associated with heat-induced mitigation of HLB in citrus plants. Healthy or Las-infected citrus grapefruit plants were exposed to room temperature or to continuous heat treatment of 40 °C for 6 days.ResultsAn exhaustive total protein extraction process facilitated the identification of 107 differentially-expressed proteins in response to Las and/or heat treatment, which included a strong up-regulation of chaperones including small (23.6, 18.5 and 17.9 kDa) heat shock proteins, a HSP70-like protein and a ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO)-binding 60 kDa chaperonin, particularly in response to heat treatment. Other proteins that were generally down-regulated due to Las infection but up-regulated in response to heat treatment include RuBisCO activase, chlorophyll a/b binding protein, glucosidase II beta subunit-like protein, a putative lipoxygenase protein, a ferritin-like protein, and a glutathione S-transferase.ConclusionsThe differentially-expressed proteins identified in this study highlights a premier characterization of the molecular mechanisms potentially involved in the reversal of Las-induced pathogenicity processes in citrus plants and are hence proposed targets for application towards the development of cisgenic Las-resistant/tolerant citrus plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0942-x) contains supplementary material, which is available to authorized users.

Solar thermotherapy reduces the titer of Candidatus Liberibacter asiaticus and enhances canopy growth by altering gene expression profiles in HLB-affected citrus plants

“…Additional support for this can be found in a proteomics analysis where total protein extracts from heat-treated, Las-positive, Citrus paradisi trees were compared to healthy trees that had not undergone heat-treatment. 39 Because several of the same genes were found to be upregulated in the heat-treated trees in both the current study ( Supplementary Table 1 ) and the proteomics study by Nwugo et al , especially those chaperones associated with heat shock, it can be concluded that a common response exists. In addition, consistent patterns of regulation were found in spite of the fact that the present study was performed on Valencia sweet orange trees and the proteomics analysis was performed on Duncan grapefruit, hence, strengthening the hypothesis that common stress pathways are induced in Las-infected citrus plants through heat regardless of citrus species.…”

Citrus vascular proteomics highlights the role of peroxidases and serine proteases during Huanglongbing disease progression

“…ROS regulating enzymes are upregulated at the protein level in grapefruit after CLas infection (93,98). Citrus undergoing thermotherapy to treat HLB exhibited increased peroxidase accumulation (99). Additionally, bioinformatic analyses comparing four RNA-seq studies on HLB illustrated that tolerance is linked with the induction of redox-related genes involved in both young and mature leaf tissues (100).…”

Proteomic analyses of Citrus petiole responses to early Huanglongbing Disease

“…Previous studies generally focused on the differentially expressed genes or proteins (DEPs) mediated by CLas in leaves, fruits and roots [26,[28][29][30][31][32]. Leaves infected with CLas display yellowing and blotchy mottled appearances.…”