A stable antimicrobial peptide with dual functions of treating and preventing citrus Huanglongbing

Abstract

Citrus Huanglongbing (HLB), caused by a vector-transmitted phloem-limited bacterium Candidatus Liberibacter asiaticus (CLas), is the most devastating citrus disease worldwide. Currently, there are no effective strategies to prevent infection or to cure HLB-positive trees. Here, using comparative analysis between HLB-sensitive citrus cultivars and HLB-tolerant citrus hybrids and relatives, we identified a novel class of stable antimicrobial peptides (SAMPs). The SAMP from Microcitrusaustraliasica can rapidly kill Liberibacter crescens (Lcr), a culturable Liberibacter strain, and inhibit infections of CLas and CL. solanacearum in plants. In controlled greenhouse trials, SAMP not only effectively reduced CLas titer and disease symptoms in HLB-positive trees but also induced innate immunity to prevent and inhibit infections. Importantly, unlike antibiotics, SAMP is heat stable, making it better suited for field applications. Spray-applied SAMP was taken up by citrus leaves, stayed stable inside the plants for at least a week, and moved systemically through the vascular system where CLas is located. We further demonstrate that SAMP is most effective on α-proteobacteria and causes rapid cytosol leakage and cell lysis. The α-helix-2 domain of SAMP is sufficient to kill Lcr. Future field trials will help determine the efficacy of SAMP in controlling HLB and the ideal mode of application.

The Asian Citrus Greening Disease (Huanglongbing): Evidence Note on Invasiveness and Potential Economic Impacts for East Africa

“…Several effective and partially effective non-antibiotic antimicrobial compounds including metals and natural products have been identified and the developments in pure culturing of CLas are opening the door to the use of genetics-based methods to understand and mitigate the spread of HLB. A recent discovery of a novel class of heat-stable antimicrobial peptides (SAMPs) which effectively kills the HLB-causing bacterium has been developed from greening-tolerant Australian finger lime and other wild citrus relatives (Huang et al, 2021). This natural plant product is reportedly safe to humans, systemic and long lasting and will be further enhanced with proprietary injection technology.…”

“…Raf.) and the "LB8-9" Sugar Belle® mandarin hybrid (SB; "Clementine" mandarin × "Minneola" tangelo) (Gmitter et al, 2010) show apparent HLB tolerance under natural HLB-endemic conditions in Florida (Deng et al, 2019), whilst SB mandarin and "Bearss" lemon trees also maintain vigorous growth and fruit yield compared to many sensitive sibling mandarin cultivars; HLB-tolerant citrus relatives also include Australian finger lime (Microcitrus australasica), Australian desert lime (Eremocitrus glauca), Hawaiian mock orange (M. paniculata) and Khasi papeda (Citrus latipes) (Huang et al, 2021). Orange, mandarin and lemon represent three different kinds of citrus from the taxonomic point of view (Wu et al, 2014).…”

Discovery of Novel GMPS Inhibitors of Candidatus Liberibacter Asiaticus by Structure Based Design and Enzyme Kinetic

“…Despite the positive effect of using broad-spectrum antibiotics to control CLas [9][10][11], these antimicrobials present two significant downsides: the emergence of bacterial resistance and impact on native bacterial populations [12,13]. Small moleculars specifically targeting CLas have also been identified [14][15][16]. In addition, plant defense inducers or activators may help decrease the influence of HLB [17][18][19].…”

A promising plant defense peptide against citrus Huanglongbing disease

“…The inability to culture HLB pathogens has significantly hampered our understanding of the virulence mechanisms of HLB and the development of HLB control approaches (3,5). In PNAS, Huang et al (6) characterize a heat-stable antimicrobial peptide MaSAMP from HLB-tolerant Microcitrus that both kills CLas and induces plant immunity (Fig. 1), representing a potential breakthrough for HLB control.…”

“…Unlike most plant pathogens, CLas that has colonized the phloem is shielded from many environmental stresses, such as ultraviolet (UV) radiation, heat, and drought, that microbes commonly encounter (10), and from chemical treatments. Huang et al identify an efficient antimicrobial peptide that can reach the phloem to kill CLas, thereby reducing HLB symptoms and preventing new CLas infections, as suggested by the data from greenhouse trials (6).…”