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An effector from the Huanglongbing-associated pathogen targets citrus proteases.

  • Author(s): Clark, Kelley;
  • Franco, Jessica Yvette;
  • Schwizer, Simon;
  • Pang, Zhiqian;
  • Hawara, Eva;
  • Liebrand, Thomas WH;
  • Pagliaccia, Deborah;
  • Zeng, Liping;
  • Gurung, Fatta B;
  • Wang, Pengcheng;
  • Shi, Jinxia;
  • Wang, Yinsheng;
  • Ancona, Veronica;
  • van der Hoorn, Renier AL;
  • Wang, Nian;
  • Coaker, Gitta;
  • Ma, Wenbo
  • et al.
Abstract

The citrus industry is facing an unprecedented challenge from Huanglongbing (HLB). All cultivars can be affected by the HLB-associated bacterium 'Candidatus Liberibacter asiaticus' (CLas) and there is no known resistance. Insight into HLB pathogenesis is urgently needed in order to develop effective management strategies. Here, we use Sec-delivered effector 1 (SDE1), which is conserved in all CLas isolates, as a molecular probe to understand CLas virulence. We show that SDE1 directly interacts with citrus papain-like cysteine proteases (PLCPs) and inhibits protease activity. PLCPs are defense-inducible and exhibit increased protein accumulation in CLas-infected trees, suggesting a role in citrus defense responses. We analyzed PLCP activity in field samples, revealing specific members that increase in abundance but remain unchanged in activity during infection. SDE1-expressing transgenic citrus also exhibit reduced PLCP activity. These data demonstrate that SDE1 inhibits citrus PLCPs, which are immune-related proteases that enhance defense responses in plants.

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