Abstract
Mounting evidence has indicated that beneficial rhizobacteria can suppress foliar pathogen invasion via elicitation of induced systemic resistance (ISR). However, it remains elusive whether long non-coding RNAs (lncRNAs) are involved in the mediation of the rhizobacteria-primed ISR processes in plants. Herein, we demonstrated the ability of the rhizobacterial strain Bacillus subtilis SL18r to trigger ISR in tomato plants against the foliar pathogen Botrytis cinerea. Comparative transcriptome analysis was conducted to screen differentially expressed lncRNAs (DELs) between the non-inoculated and SL18r-inoculated plants. Among these DELs, four variants of MSTRG18363 possessed conserved binding sites for miR1918, which negatively regulates immune systems in tomato plants. The expression of MSTRG18363 in tomato leaves was significantly induced by SL18r inoculation. The transcription of MSTRG18363 was negatively correlated with the expression of miR1918, but displayed a positive correlation with the transcription of the RING-H2 finger gene SlATL20 (a target gene of miR1918). Moreover, MSTRG18363-overexpressing plants exhibited the enhanced disease resistance, reduction of miR1918 transcripts, and marked increases of SlATL20 expression. However, the SL18r-induced disease resistance was largely impaired in the MSTRG18363-silenced plants. VIGS-mediated SlATL20 silencing also greatly weakened the SL18r-induced disease resistance. Collectively, our results suggested that induction of MSTRG18363 expression in tomato plants by SL18r was conducive to promoting the decoy of miR1918 and regulating the expression of SlATL20, thereby provoking the ISR responses against foliar pathogen infection.
Highlights
In plants, a series of intricate strategies has been evolved to defend against pathogenic bacteria, fungi and virus
Seven-day-old tomato seedlings were firstly cultured in soil for 3 weeks and were poured with cell suspension of SL18r at the different concentrations of 4 × 106, 2 × 107, and 1 × 108 CFU g−1 of soil for 3 days, respectively, and tomato plants treated with the phosphate buffered saline (PBS) solution were used as the control
DAB staining showed that the production of H2O2 were notably less in leaves of tomato plants treated with higher inoculum dosage of SL18r compared with the controls (Figure 1C)
Summary
A series of intricate strategies has been evolved to defend against pathogenic bacteria, fungi and virus. Apart from basal immune systems that can be stimulated at the pathogen-infected sites, a primed defense strategy has been developed by plants, in which defense responses have not been activated for increasing plant’s resistance, but is attributable to quicker induction of defenserelated signaling pathways upon exposure to the attacks of pathogens (Bostock, 2005). Well-studied examples of inducible defenses in plants are the activated systemic acquired resistance (SAR) by necrosisinducing pathogen infection (Grant and Lamb, 2006). Rhizobacteria strain B. subtilis FB17 has been reported to activate both the SA- and ABA-related pathways to prevent the stomata-mediated entering routes of foliar pathogen into Arabidopsis plants (Kumar et al, 2012). Bacillus cereus AR156 can provoke ISR of Arabidopsis plants against pathogenic bacteria via stimulation of the JA-/ET- and SA-related pathways (Nie et al, 2017)
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