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

Citrus Huanglongbing (HLB), caused by a vector-transmitted phloem-limited bacterium Liberibacter asiaticus (Las), 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 can rapidly kill (), a culturable Liberibacter strain, and inhibit infections of Las and L. solanacearum in plants. In controlled greenhouse trials, SAMP not only effectively reduced Las 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 Las 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 Future field trials will help determine the efficacy of SAMP in controlling HLB and the ideal mode of application.