Lack of a Cytoplasmic RLK, Required for ROS Homeostasis, Induces Strong Resistance to Bacterial Leaf Blight in Rice.

Youngchul Yoo,Jungil Yang,Jong-Chan Park,Ki-Hong Jung,Chi-Yeol Kim,Gynheung An,Jong-Seong Jeon,Man-Ho Cho,Sang-Won Lee

doi:10.3389/fpls.2018.00577

Abstract

Many scientific findings have been reported on the beneficial function of reactive oxygen species (ROS) in various cellular processes, showing that they are not just toxic byproducts. The double-edged role of ROS shows the importance of the regulation of ROS level. We report a gene, rrsRLK (required for ROS-scavenging receptor-like kinase), that encodes a cytoplasmic RLK belonging to the non-RD kinase family. The gene was identified by screening rice RLK mutant lines infected with Xanthomonas oryzae pv. oryzae (Xoo), an agent of bacterial leaf blight of rice. The mutant (ΔrrsRLK) lacking the Os01g02290 gene was strongly resistant to many Xoo strains, but not to the fungal pathogen Magnaporthe grisea. ΔrrsRLK showed significantly higher expression of OsPR1a, OsPR1b, OsLOX, RBBTI4, and jasmonic acid-related genes than wild type. We showed that rrsRLK protein interacts with OsVOZ1 (vascular one zinc-finger 1) and OsPEX11 (peroxisomal biogenesis factor 11). In the further experiments, abnormal biogenesis of peroxisomes, hydrogen peroxide (H2O2) accumulation, and reduction of activity of ROS-scavenging enzymes were investigated in ΔrrsRLK. These results suggest that the enhanced resistance in ΔrrsRLK is due to H2O2 accumulation caused by irregular ROS-scavenging mechanism, and rrsRLK is most likely a key regulator required for ROS homeostasis in rice.

Highlights

Despite the massive efforts of international organizations and scientists to solve food problems, 108 million people world-wide face serious food insecurities (Arthur, 2008)
In addition to the evidence that reactive oxygen species (ROS) contribute to plant development, it has been suggested that they play a role as rapidly generated signal molecules in response to stresses (Stael et al, 2015)
The additional ROS in apoplasts enter the cell via aquaporin to alter cellular processes such as activation of defense responses, regulation of photosynthesis, modulation of hormonal responses, and inhibition of growth and development (Mittler and Blumwald, 2015)

Summary

Introduction

Despite the massive efforts of international organizations and scientists to solve food problems, 108 million people world-wide face serious food insecurities (Arthur, 2008). There are diverse causes that reduce the productivity of crops, and losses by biotic invaders are serious These situations illustrate the importance of research on crop defense systems against small pathogens such as viruses, bacteria, and fungi. Since the gene-for-gene hypothesis was proposed (Flor, 1971), plant defense systems have been largely concentrated in two types Both are known to be triggered by interactions between pathogen elicitors and host plant receptors. Plants have cytoplasmic receptors that sense pathogenic effectors delivered through type three secretion systems (Jones and Dangl, 2006). The second type of defense system (called Effector-Triggered Immunity, ETI) usually causes programmed cell death (Cunnac et al, 2009) and induces much stronger and strain-specific responses compared to PTI (Jones and Dangl, 2006). In response to the defense mechanisms of host plants, pathogens have evolved to avoid recognition by receptors for PTI/ETI through either lost or altered effector (Thomma et al, 2011), but host plants have evolved to detect such changes in pathogens (Almagro et al, 2009)

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Conclusion