Abstract
Citrus huanglongbing (HLB) is a highly destructive disease of citrus presumably caused by ‘ Candidatus Liberibacter asiaticus ’ (Las), a gram-negative, insect-transmitted, phloem-limited α-proteobacterium. Although almost all citrus plants are susceptible to HLB, reports have shown reduced susceptibility to Las infection in lemon ( Citrus limon ) plants. The aim of this study is to identify intra-species specific molecular mechanisms associated with Las-induced responses in lemon plants. To achieve this, comparative 2-DE and mass spectrometry, in addition to Inductively Coupled Plasma Spectroscopy (ICPS) analyses, were applied to investigate differences in protein accumulation and the concentrations of cationic elements in leaves of healthy and Las-infected lemon plants. Results showed a differential accumulation of 27 proteins, including an increase in accumulation of starch synthase but decrease in the production of photosynthesis-related proteins in Las-infected lemon plants compared to healthy plants. Furthermore, there was a 6% increase (P > 0.05) in K concentration in leaves of lemon plants upon Las infection, which support results from previous studies and might represent a common response pattern of citrus plants to Las infection. Interestingly, contrary to reports from prior studies, this study showed a general reduction in the production of defense-related pathogen-response proteins but a 128% increase in Zn concentration in lemon plants in response to Las infection. Taken together, this study sheds light on general and intra-species specific responses associated with the response of citrus plants to Las.
Highlights
Citrus Huanglongbing (HLB), previously known as citrus greening disease is arguably the most devastating disease threatening citrus production worldwide and all cultivated citrus species are susceptible [1,2,3]
Liberibacter asiaticus’ (Las) infection had no significant effect on total protein yield in leaves of lemon plants and an average total protein yield of 12.2 mg g-1 or 13.9 mg g-1 was obtained from leaves of healthy or Las-infected leaves, respectively (Table 1)
This study showed that Las infection resulted in a downregulation of photosynthesis-related proteins but an upregulation of granule-bound starch synthase accompanied by a 6% increase (P > 0.05) in K concentration of lemon plants
Summary
Citrus Huanglongbing (HLB), previously known as citrus greening disease is arguably the most devastating disease threatening citrus production worldwide and all cultivated citrus species are susceptible [1,2,3]. Several reports on plant-microbe interactions suggest that there are highly conserved pathogen-derived molecules, such as flagellin, that generate a generalized or non-host specific molecular response in plants, referred to as nonhost response [4,5,6]. This response involves an increased production of defense-related proteins such as cysteine proteases, thaumatin-like proteins, chitinases, superoxide dismutase, peroxidases and catalase in the host plants [7]. A high-throughput transcriptional analysis study of innate responses of Arabidopsis plants showed a strong overlap in the production of nonhost and host-specific proteins in the presence of flagellin, highlighting the power of highthroughput technologies in identifying overall host responses to plant pathogens while noting that understanding plant-microbe interactions is still a complex subject [10]
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