Whole-Genome Sequence of Bacillus cereus AR156, a Potential Biocontrol Agent with High Soilborne Disease Biocontrol Efficacy and Plant Growth Promotion.

Bacillus cereus AR156 was originally isolated from the forest soil of Zhenjiang, a city in China. To shed new light on the molecular mechanisms underlying the biological control of soilborne pathogens, the whole genome of this strain was sequenced. Here, we report the draft genome sequence of this strain, consisting of a single circularized contig measuring 5.66 Mb, with an average GC content of 35.5% and 5,367 open reading frames.

Bacillus cereus AR156 Extracellular Polysaccharides Served as a Novel Micro-associated Molecular Pattern to Induced Systemic Immunity to Pst DC3000 in Arabidopsis.

Non-host resistance (NHR) is a broad-spectrum plant defense. Upon colonizing on the surface on the root or leaves of non-host species, pathogens initial encounter preform and induce defense response in plant, such as induced hypersensitive response, PAMPs triggered immunity (PTI), and effector triggered immunity (ETI). The ability of plants to develop an induced systemic response (ISR) in reaction to the colonization by non-pathogenic rhizobacterium depends on interactions between host plants and the colonizing rhizobacterium, and the ISR also can be defined as a NHR. However, how the colonization signal is and how systemic resistance to pathogens is developed is still unclear. In this study, we demonstrated that the extracellular polysaccharides (EPSs) of Bacillus cereus AR156 could act as novel microbe-associated molecular patterns (MAMPs) and function in the early perception status of the ISR of B. cereus AR156. The results revealed that B. cereus AR156 EPS could induce systemic resistance to Pst DC3000 in Arabidopsis. Cellular defense response markers such as hydrogen peroxide accumulation, callose deposition, and defense-associated enzyme were induced upon challenge inoculation in the leaves primed by EPS. Moreover, the defense-related genes PR1, PR2, and PR5 and mitogen-activated kinases (MAPK) cascade marker gene MPK6 were concurrently expressed in the leaves of EPS-treated plants and induced higher resistance to Pst DC3000 in Col-0 than that in the jar1 or etr1 mutants. The protection was absent in the NahG transgenic plants and npr1 mutant, suggesting an activation of the salicylic acid (SA)- and the MAPK-dependent signaling pathways with NPR1-dependent by B. cereus AR156 EPS. In conclusion, B. cereus AR156 EPS play an important role in MAMP perception during the process of rhizobacteria-triggered NHR. This study is the first to illustrate how AR156 induces systemic resistance to Pst DC3000 in Arabidopsis. It also provides the first explanation of how plants perceive colonization of non-pathogenic bacteria and how rhizobacteria trigger ISR to plant pathogens.

Transcription factors WRKY70 and WRKY11 served as regulators in rhizobacterium Bacillus cereus AR156-induced systemic resistance to Pseudomonas syringae pv. tomato DC3000 in Arabidopsis.

The activation of both the SA and JA/ETsignalling pathways may lead to more efficient general and broad resistance to Pst DC3000 by non-pathogenic rhizobacteria. However, the mechanisms that govern this simultaneous activation are unclear. Using Arabidopsis as a model system, two transcription factors, WRKY11 and WRKY70, were identified as important regulators involved in Induced Systemic Resistance (ISR) triggered by Bacillus cereus AR156. The results revealed that AR156 treatment significantly stimulated the transcription of WRKY70, but suppressed that of WRKY11 in Arabidopsis leaves. Furthermore, they were shown to be required for AR156 enhancing the activation of cellular defence responses and the transcription level of the plant defence response gene. Overexpression of the two transcription factors in Arabidopsis also showed that they were essential for AR156 to elicit ISR. AR156-triggered ISR was completely abolished in the double mutant of the two transcription factors, but still partially retained in the single mutants, indicating that the regulation of the two transcription factors depend on two different pathways. The target genes of the two transcription factors and epistasis analysis suggested that WRKY11 regulated AR156-triggered ISR through activating the JA signalling pathway, and WRKY70 regulated the ISR through activating the SA signalling pathway. In addition, both WRKY11 and WRKY70 modulated AR156-triggered ISR in a NPR1-dependent manner. In conclusion, WRKY11 and WRKY70 played an important role in regulating the signalling transduction pathways involved in AR156-triggered ISR. This study is the first to illustrate the mechanism by which a single rhizobacterium elicits ISR by simultaneously activating both the SA and JA/ET signalling pathways.

Effects of the sequence characteristics of miRNAs on multi-viral resistance mediated by single amiRNAs in transgenic tobacco.

Artificial microRNA (amiRNA) has become the preferred viral defence that can be induced in plants. In this study, nine amiRNA target sites were selected that were based on the sequence characteristics of natural miRNAs in the cylindrical inclusion protein (CI), nuclear inclusion a protein (NIa), nuclear inclusion b protein (NIb), and coat protein (CP) genes of Potato virus Y (PVY(N)). These amiRNAs that exhibited high similarities to the sequences of PVY(N) and TEV-SD1 were considered. To study the effectiveness of gene silencing in amiRNA-mediated viral resistance, we constructed nine amiRNA plant expression vectors by replacing the functional sequences of miRNA319a precursors with our selected amiRNA sequences. These constructs were subsequently introduced to tobacco plants. A Northern blot assay verified that the nine amiRNA plant expression vectors could successfully express amiRNAs in plants. The analysis of viral resistance demonstrated that these transgenic tobacco plants could effectively inhibit PVY(N) and TEV-SD1 viral infections. The amiRNA that targeted the NIb and CP genes displayed a higher silencing efficiency than did the amiRNAs targeted CI and NIa genes. Northern blot analysis demonstrated that silencing was induced by the original amiRNAs and could be bilaterally extended by the siRNA pathway. That is, the amiRNA and the secondary siRNA mediated the degradation of viral RNA together. Genetic analysis demonstrated that the trait for viral resistance in transgenic plants can be consistently inherited via a single copy of the transgenic sequence. Considering the correlation between the sequence characteristics and the activity of amiRNA, we concluded that a few mismatched bases between the amiRNA and the target sequence could be allowed, particularly the mismatched bases in the 3' end of the amiRNA.