Oryza-Specific Orphan Protein Triggers Enhanced Resistance to Xanthomonas oryzae pv. oryzae in Rice

Abstract

All genomes carry lineage-specific orphan genes lacking homology in their closely related species. Identification and functional study of the orphan genes is fundamentally important for understanding lineage-specific adaptations including acquirement of resistance to pathogens. However, most orphan genes are of unknown function due to the difficulties in studying them using helpful comparative genomics. Here, we present a defense-related Oryza-specific orphan gene, Xio1, specifically induced by the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) in an immune receptor XA21-dependent manner. Salicylic acid (SA) and ethephon (ET) also induced its expression, but methyl jasmonic acid (MeJA) reduced its basal expression. C-terminal green fluorescent protein (GFP) tagged Xio1 (Xio1-GFP) was visualized in the nucleus and the cytosol after polyethylene glycol (PEG)-mediated transformation in rice protoplasts and Agrobacterium-mediated infiltration in tobacco leaves. Transgenic rice plants overexpressing Xio1-GFP showed significantly enhanced resistance to Xoo with reduced lesion lengths and bacterial growth, in company with constitutive expression of defense-related genes. However, all of the transgenic plants displayed severe growth retardation and premature death. Reactive oxygen species (ROS) was significantly produced in rice protoplasts constitutively expressing Xio1-GFP. Overexpression of Xio1-GFP in non-Oryza plant species, Arabidopsis thaliana, failed to induce growth retardation and enhanced resistance to Pseudomonas syringae pv. tomato (Pst) DC3000. Our results suggest that the defense-related orphan gene Xio1 plays an important role in distinctive mechanisms evolved within the Oryza and provides a new source of Oryza-specific genes for crop-breeding programs.

Rice small secreted peptide, OsRALF26, recognized by FERONIA‐like receptor 1 induces immunity in rice and Arabidopsis

“…To induce plasmolysis, leaves were incubated in 0.8 m mannitol (Biobasic) solution for 30 min. Rice protoplast isolation and polyethylene glycol (PEG)‐mediated transformation were carried out following a previous report (Bart et al., 2006; Moon et al., 2022). Fluorescent signals in leaves were photographed using a fluorescence microscope Eclipse Ti (Nikon, Tokyo, Japan), fitted with an objective (200×).…”

The Lost and Found: Unraveling the Functions of Orphan Genes

“…With the advancements in sequencing technologies, the number of sequenced genomes has been increasing, leading to the discovery of new OGs ( Figure 2 ). This led to the conclusion that OGs can be found in almost every genome with their specific roles in various biological processes, including metabolism, immunomodulation, stress biology, and other species-specific adaptive processes [ 8 , 28 , 50 ].…”

“…Moreover, OGs have also been shown to play a role in stress resistance and immune regulation [ 28 , 64 , 102 ]. For instance, AtQQS in Arabidopsis and soybean confers resistance against pathogens and pests, and TaFROG enhances resistance against the mycotoxigenic fungus Fusarium graminearum ( F. graminearum ) [ 26 ].…”

Research Advances and Prospects of Orphan Genes in Plants

“…A defense-related Oryza-specific orphan gene Xio1 (Xoo-induced orphan 1) specifically induced by the bacterial pathogen X. oryzae pv. oryzae (Xoo) in an immune receptor XA21-dependent manner (Moon et al, 2022). Overexpression of Xio1 showed enhanced resistance to Xoo and reactive oxygen species accumulation.…”