Yoo Y, Park JC, Cho MH, Yang J, Kim CY, Jung KH, Jeon JS, An G, Lee SW.

Front Plant Sci. 2018 May 18;9:577. 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.

See https://www.ncbi.nlm.nih.gov/pubmed/29868050

Figure 1: (A) Schematic representation of T-DNA insertion (+480 bp from the translational start site) at Os01g02290 encoding rrsRLK in Dongjin (ΔrrsRLK_dj). ATG start codon and TGA stop codon are indicated. Os01g02290 consists of four exons (black boxes) and three introns (line between the black boxes). (B) Expression analysis of the rrsRLK gene in SE-WT_dj (segregated wild type) and ΔrrsRLK_dj mutant lines using RT-PCR with rrsRLK primers. Ubi gene was used as an internal control. The experiment was repeated three times with consistent results. (C) Comparison of lesion development on leaves of SE-WT_dj and homozygous mutant lines of ΔrrsRLK_dj. Rice plants grown for 6 weeks were inoculated with PXO99 and monitored for lesion development for 14 DAI. The results were consistent until the 6th generation of the mutant, and each experiment was carried out with more than 40 leaves. (D) Lesion lengths scored at 14 DAI on leaves of SE-WT_dj and ΔrrsRLK_dj mutant lines. The averages and error ranges of each sample were calculated from 40 leaves. Asterisk indicates P < 0.05 (Student’s t-test). Data in (C,D) are results of experiments carried out using the 3rd generation of ΔrrsRLK_dj mutant lines. (E) Bacterial population extracted from inoculated leaves of SE-WT_dj and ΔrrsRLK_dj mutant lines at 0 and 14 DAI. Xoo was extracted from inoculated leaves and incubated on PSA plates after serial dilution for colony counting. Each data point represents the average and standard deviation of three biological replicates. The experiment was repeated three times with similar results. Different letters above bars indicate statistically significant differences as determined by one-way analysis of variance (ANOVA: ^∗, a, b, c), P < 0.05.