Bacillus cereus AR156 triggers induced systemic resistance against Pseudomonas syringae pv. tomato DC3000 by suppressing miR472 and activating CNLs-mediated basal immunity in Arabidopsis.

Chunhao Jiang,Zhihang Fan,Yan Li,Zijie Li,Hailing Jin,Qi Wang,Dongdong Niu,Jianhua Guo,Mingzi Zheng

doi:10.1111/mpp.12935

Abstract

Small RNAs play an important role in plant innate immunity. However, their regulatory function in induced systemic resistance (ISR) triggered by plant growth‐promoting rhizobacteria remains unclear. Here, using Arabidopsis as a model system, one plant endogenous small RNA, miR472, was identified as an important regulator involved in the process of Bacillus cereus AR156 ISR against Pseudomonas syringae pv. tomato (Pst) DC3000. The results revealed that miR472 was down‐regulated with B. cereus AR156 treatment by comparing small RNA profiles and northern blot analysis of Arabidopsis with or without B. cereus AR156 treatment. Plants overexpressing miR472 showed higher susceptibility to Pst DC3000; by contrast, plant lines with miR472 knocked down/out showed the opposite. The transcriptome sequencing revealed thousands of differentially expressed genes in the transgenic plants. Target prediction showed that miR472 targets lots of coiled coil nucleotide‐binding site (NBS) and leucine‐rich repeat (LRR) type resistance genes and the expression of these targets was negatively correlated with the expression of miR472. In addition, transgenic plants with knocked‐out target genes exhibited decreased resistance to Pst DC3000 invasion. Quantitative reverse transcription PCR results indicated that target genes of miR472 were expressed during the process of B. cereus AR156‐triggered ISR. Taken together, our results demonstrate that the miR472‐mediated silencing pathway is an important regulatory checkpoint occurring via post‐transcriptional control of NBS‐LRR genes during B. cereus AR156‐triggered ISR in Arabidopsis.

Highlights

To survive in a complex and hostile soil environment, plants have evolved multiple types of inducible immune responses to attacks by pathogens (Niu et al, 2016)
We identified one small RNA, miR472, whose expression was significantly down-regulated by combined treatment with AR156 and Pst DC3000, but only in Arabidopsis plants pretreated with AR156 (Figure 1c–e)
We evaluated the effects of miR472 on AR156induced systemic resistance in Arabidopsis

Summary

| INTRODUCTION

To survive in a complex and hostile soil environment, plants have evolved multiple types of inducible immune responses to attacks by pathogens (Niu et al, 2016). The leaves of wild-type Col-0 plants pretreated with AR156 and inoculated with Pst DC3000 showed significantly decreased (p < .01) pathogen density at 3 and 4 dpi compared with that of respective controls inoculated with Pst DC3000 only; by contrast, the density of Pst DC3000 on the leaves of STTM472-1# and SALK_087945-1# remained constant irrespective of pretreatment with AR156 (Figure 3g) These results indicate that AR156-triggered ISR was abolished in miR472 mutant lines. Compared with Col-0 wild-type plants, the five CNL lines showed increased susceptibility to disease, which was manifested as stronger yellowing or chlorosis in leaves (Figure 6b) These results indicate that the five identified targets of miR472 positively regulate disease resistance, thereby further clarifying the role of miR472 in regulating the defence response. Our results indicate that the target genes of miR472 were coordinately expressed

| DISCUSSION

Findings

| EXPERIMENTAL PROCEDURES