Abstract
Wheat stripe rust, due to infection by Puccinia striiformis f. sp. tritici (Pst), is a devastating disease that causes significant global grain yield losses. Yr36, which encodes 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 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 Pst-infected regions, but the underlying mechanisms remain elusive. Here, we show that WKS1 interacts with and phosphorylates PsbO, an extrinsic member of photosystem II (PSII), to reduce photosynthesis, regulate leaf chlorosis, and confer Pst resistance. A point mutation in PsbO-A1 or reduction 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 physical interactions with PSII and reduces the binding affinity of PsbO with PSII. Presumably, phosphorylated PsbO proteins dissociate from the PSII complex and then undergo rapid degradation by cysteine and aspartic proteases. Taken together, these results demonstrate that perturbations of wheat PsbO by point mutation or phosphorylation by WKS1 reduce the rate of photosynthesis and delay the growth of Pst pathogen before the induction of ROS.
Highlights
Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici ( Pst), has been the most substantial biotrophic challenge to wheat production in the last two decades (Schwessinger, 2017)
Using a previously tested Pubi:TAP-Wheat Kinase START1 (WKS1).1 transgenic line (Gou et al, 2015), we performed a co-immunoprecipitation (Co-IP) experiment using soluble protein from fully expanded leaves that were not inoculated with Pst and observed that phosphorylated by 0.2 mg of WKS1.1 (PsbO) co-precipitated with WKS1.1 (Supplemental Figure 1)
These results were consistent with the chloroplast localization of PsbO-GFP fusion proteins (Supplemental Figure 2), as well as with previous results showing that WKS1.1 could be transported into chloroplasts (Gou et al, 2015; Li et al, 2017)
Summary
Wheat stripe rust (or yellow rust [Yr]), caused by Puccinia striiformis f. sp. tritici ( Pst), has been the most substantial biotrophic challenge to wheat production in the last two decades (Schwessinger, 2017). Tritici ( Pst), has been the most substantial biotrophic challenge to wheat production in the last two decades (Schwessinger, 2017). Molecular Plant 12, 1639–1650, December 2019 a The Author 2019. WKS1 Phosphorylates PsbO to Confer Pst Resistance lost to the pathogen annually (Beddow et al, 2015). To feed and improve the food supply for an increasing human population (according to the FAOSTAT database for 2017; http://www.fao.org/faostat/en/#home), it is essential to reduce yield losses caused by Pst (Chen et al, 2014). Reducing yield losses caused by fungal diseases is an efficient avenue for increasing wheat production. Chemical control is available for wheat fungal pathogens, planting resistant cultivars is a more cost-effective and environmentally friendly alternative (Ellis et al, 2014)
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