Study on Citrus Response to Huanglongbing Highlights a Down-Regulation of Defense-Related Proteins in Lemon Plants Upon ‘Ca. Liberibacter asiaticus’ Infection

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.

High Incidence of Preharvest Colonization of Huanglongbing-Symptomatic Citrus sinensis Fruit by Lasiodiplodia theobromae (Diplodia natalensis) and Exacerbation of Postharvest Fruit Decay by That Fungus

“…Liberibacter asiaticus" lacks type II plant cell wall-degrading enzymes (54), which have been known to play important roles in plant signaling to induce defense responses against fungal pathogens through autodegradation products of the plant cell wall (cell wall fragments or oligogalacturonides) (53). Moreover, studies have shown that the plant defense system is suppressed by HLB disease (42,52,55,56). This weakened defense system in HLB-affected citrus trees could explain their increased susceptibility to other pathogens such as diplodia.…”

Can CRISPR Win the Battle against Huanglongbing?

“…The 56 down-regulated proteins were associated with protein synthesis, protein folding and photosynthesis. On the contrary, the defense-related proteins were down-regulated in lemon that is tolerant to HLB, such as lectin-related proteins, chitinase, and miraculin-like proteins [37]. Upon HLB infection, chaperones HSP 70 and an isoflavone reductase-related protein were up-regulated in lemon.…”

“…Upon HLB infection, chaperones HSP 70 and an isoflavone reductase-related protein were up-regulated in lemon. Proteins associated with photosynthesis and starch synthesis were similar to grapefruit and sweet orange [37]. The differences in responses between HLB susceptible and tolerant cultivars were determined by proteomes between Navel orange (susceptible) and Volkameriana (moderately tolerant) [38].…”

Efecto del HLB sobre el rendimiento de limón mexicano en Colima, México

“…This can cause a sharp reduction of the photosyntates production in those leaves as pointed by (Nwugo et al, 2013;Xu et al, 2015). In some cases there is also a premature leaf drop (Robles-González et al, 2010).…”

“…Esto puede provocar una fuerte reducción en la producción de fotosintatos en esas hojas como lo señalan (Nwugo et al, 2013;Xu et al, 2015). En algunos casos se presenta además la caída prematura de hojas (Robles-González et al, 2010).…”