Plasma membrane localization is essential for Oryza sativa Pto-interacting protein 1a-mediated negative regulation of immune signaling in rice.

Hidenori Matsui,Satoshi Hamada,Hirohiko Hirochika,Akira Takahashi,Masayuki Fujiwara,Ko Shimamoto,Hirofumi Nakagami,Yuko Nomura

doi:10.1104/pp.114.243873

Abstract

Oryza sativa Pto-interacting protein 1a (OsPti1a), an ortholog of tomato (Solanum lycopersicum) SlPti1, functions as a negative regulator of innate immunity in rice (Oryza sativa). In ospti1a mutants, the activation of immune responses, including hypersensitive response-like cell death, is caused by loss of the OsPti1a protein; however, it is as yet unclear how OsPti1a suppresses immune responses. Here, we report that OsPti1a localizes to detergent-resistant membrane fractions of the plasma membrane through lipid modification of the protein's amino terminus, which is highly conserved among Pti1 orthologs in several plant species. Importantly, mislocalization of OsPti1a after deletion of its amino terminus reduced its ability to complement the mutant phenotypes, including hypersensitive response-like cell death. Furthermore, complex formation of OsPti1a depends on its amino terminus-mediated membrane localization. Liquid chromatography-tandem mass spectrometry analysis of OsPti1a complex-interacting proteins identified several defense-related proteins. Collectively, these findings indicate that appropriate complex formation by OsPti1a at the plasma membrane is required for the negative regulation of plant immune responses in rice.

Highlights

Oryza sativa Pto-interacting protein 1a (OsPti1a), an ortholog of tomato (Solanum lycopersicum) SlPti1, functions as a negative regulator of innate immunity in rice (Oryza sativa)
To elucidate the biological and physiological roles of OsPti1a in vivo, we investigated the subcellular localization of OsPti1a protein by cellular fractionation of rice suspension culture cells
OsPti1a protein with deletions of only 10 amino acids in the N terminus lost the ability to complement the knockout mutant phenotype. These results indicate that the N-terminal region of the OsPti1a protein is essential for suppressing defense activation in rice

Summary

Introduction

Oryza sativa Pto-interacting protein 1a (OsPti1a), an ortholog of tomato (Solanum lycopersicum) SlPti, functions as a negative regulator of innate immunity in rice (Oryza sativa). Liquid chromatography-tandem mass spectrometry analysis of OsPti1a complexinteracting proteins identified several defense-related proteins These findings indicate that appropriate complex formation by OsPti1a at the plasma membrane is required for the negative regulation of plant immune responses in rice. We reported that knockout mutations of the Oryza sativa Pto-interacting protein 1a (OsPti1a) gene, which encodes a Ser/Thr protein kinase, activate a series of defense responses in rice (Oryza sativa) accompanied by hypersensitive response-like lesion formation over the entire leaf surface in the absence of pathogen challenge (Takahashi et al, 2007). We reported that overexpression of OsPti1a results in enhanced susceptibility against compatible pathogens and reduces resistance against an incompatible race of rice blast fungus (Takahashi et al, 2007) These results suggest that OsPti1a functions as a negative regulator of both MTI and ETI in rice (Takahashi et al, 2007). OsPti1a-mediated basal defense is regulated by the phosphorylation of a conserved Thr through the upstream kinases rice oxidative signal-inducible (OsOxi1) and rice phosphoinositidedependent protein kinase (OsPdk; Matsui et al, 2010a, 2010b); it is still not clear how OsPti1a negatively regulates signaling to activate defense responses

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