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YR36/WKS1-mediated Phosphorylation of PsbO, an Extrinsic Member of Photosystem II, Inhibits Photosynthesis and Confers Stripe Rust Resistance in Wheat.

  • Author(s): Wang, Shuai
  • Li, Qiu-Ping
  • Wang, Jianfeng
  • Yan, Yan
  • Zhang, Guo-Liang
  • Yan, Yan
  • Zhang, Huifei
  • Wu, Jiajie
  • Chen, Feng
  • Wang, Xiaojie
  • Kang, Zhensheng
  • Dubcovsky, Jorge
  • Gou, Jin-Ying
  • et al.
Abstract

Wheat stripe rust, due to infection by Puccinia striiformis f. sp. tritici (Pst), is a devastating disease that is causing significant global grain yield losses. Yr36, which encodes the Wheat Kinase START1 (WKS1), is an effective high-temperature adult-plant resistance gene and confers resistance to a broad spectrum of Pst races. We previously showed that WKS1 phosphorylates the thylakoid ascorbate peroxidase (tAPX) protein and reduces its ability to detoxify peroxides, which may contribute to the accumulation of reactive oxygen species (ROS). WKS1-mediated Pst resistance is accompanied by leaf chlorosis in the Pst-infected regions, but the underlying mechanisms remain still elusive. Here, we show that WKS1 interacts with and phosphorylates PsbO, an extrinsic member of photosystem II (PSII), to reduce photosynthesis and regulate leaf chlorosis in conferring Pst resistance. A point mutation in PsbO-A1 or reductions in its transcript levels by RNA interference resulted in chlorosis and reduced Pst sporulation. Biochemical analyses revealed that WKS1 phosphorylates PsbO at two conserved amino acids involved in its physical interactions with PSII and reduces the binding affinity of PsbO to PSII. Phosphorylated PsbO dissociated from the PSII protein complex, and underwent fast degradation by cysteine and aspartic proteases. Taken together, these results demonstrate that perturbations of wheat PsbO by point mutation or its phosphorylation by WKS1 reduce photosynthesis rate and delays the growth of Pst pathogen before the induction of ROS.

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