A gut-derived peptide protects citrus trees from Huanglongbing

Huanglongbing is a devastating bacterial disease of citrus trees with no known cure. An emerging strategy to provide resistance to plant pathogens is disrupting genes that increase disease susceptibility. A paper in Science by Zhao et al. uses this approach in citrus trees, and identifies a regulatory circuit that can be modulated to alleviate Huanglongbing disease symptoms.

Huanglongbing can infect all citrus plants, and only some lineages naturally display tolerance or resistance. This prompted the authors to compare the transcriptional responses of different lineages upon infection. They found the E3 ubiquitin ligase PUB21 to be highly upregulated in disease-sensitive plants, but not in disease-tolerant plants. Further analysis showed that PUB21 targets MYC2 — an immune protein that is important for jasmonate-mediated defense — for degradation. PUB21 and MYC2 form a regulatory circuit, in which MYC2 binds the PUB21 promotor to induce PUB21 expression, thereby degrading MYC2. The authors found that the Huanglongbing pathogen targets this circuit by enhancing the PUB21–MYC2 interaction to suppress immune defense and promote infection.

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