Loss function of SL (sekiguchi lesion) in the rice cultivar Minghui 86 leads to enhanced resistance to (hemi)biotrophic pathogens

Dagang Tian,Fang Yang,Feng Wang,Gang Li,Qiong Luo,Mo Wang,Yuqing Niu,Yan Lin,Zaijie Chen

doi:10.1186/s12870-020-02724-6

Abstract

BackgroundSerotonin, originally identified as a neurotransmitter in mammals, functions as an antioxidant to scavenge cellular ROS in plants. In rice, the conversion of tryptamine to serotonin is catalyzed by SL (sekiguchi lesion), a member of cytochrome P450 monooxygenase family. The sl mutant, originated from rice cultivar Sekiguchi-asahi, exhibits spontaneous lesions, whereas its immune responses to pathogens have not been clearly characterized.ResultsHere we identified three allelic mutants of SL in an indica rice restore line Minghui 86 (MH86), named as sl-MH-1, − 2 and − 3, all of which present the typical lesions under normal growth condition. Compared with those in MH86, the serotonin content in sl-MH-1 is dramatically decreased, whereas the levels of tryptamine and L-trytophan are significantly increased. The sl-MH-1 mutant accumulates high H2O2 level at its lesion sites and is more sensitive to exogenous H2O2 treatment than the wild type. When treated with the reductant vitamin C (Vc), the lesion formation on sl-MH-1 leaves could be efficiently suppressed. In addition, sl-MH-1 displayed more resistant to both the blast fungus and blight bacteria, Pyricularia oryzae (P. oryzae, teleomorph: Magnaporthe oryzae) and Xanthomonas oryzae pv. Oryzae (Xoo), respectively. The pathogen-associated molecular patterns (PAMPs)-triggered immunity (PTI) responses, like reactive oxygen species (ROS) burst and callose deposition, were enhanced in sl-MH-1. Moreover, loss function of SL resulted in higher resting levels of the defense hormones, salicylic acid and jasmonic acid. The RNA-seq analysis indicated that after P. oryzae infection, transcription of the genes involved in reduction-oxidation regulation was the most markedly changed in sl-MH-1, compared with MH86.ConclusionsOur results indicate that SL, involving in the final step of serotonin biosynthesis, negatively regulates rice resistance against (hemi)biotrophic pathogens via compromising the PTI responses and defense hormones accumulation.

Highlights

Serotonin, originally identified as a neurotransmitter in mammals, functions as an antioxidant to scavenge cellular reactive oxygen species (ROS) in plants
We identified the sl mutants in Minghui 86 (MH86) background and found that the lesions of slMH-1 is caused by excessive accumulation of ROS, which could be suppressed by the reductant treatment
Identification of the sl mutants in MH86 background We have identified a rice runaway-cell death mutant, rcd1–1, in an indica rice restore line Minghui 86 (MH86)

Summary

Introduction

Originally identified as a neurotransmitter in mammals, functions as an antioxidant to scavenge cellular ROS in plants. PAMP-triggered immunity (PTI), activated upon recognition of conserved pathogenassociated molecular patterns (PAMPs) by plant cell membrane-localized pattern recognition receptors, can rapidly elicit plant defense responses, which includes calcium ions influx, reactive oxygen species (ROS) generation, callose deposition and stomatal closure et al [2]. Another branch of plant immunity is effector-triggered immunity (ETI), caused by direct or indirect perception of pathogen effectors via plant resistance (R) proteins, which is often associated with a hypersensitive response (HR) and renders plants the isolate-specific resistance [3]. The raised oxidative stress in plant cells is essential for HR formation and development [6]

Methods

Results

Discussion

Conclusion