- 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
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.