AtMC1 Associates With LSM4 to Regulate Plant Immunity Through Modulating Pre-mRNA Splicing.

Alternative splicing of pre-mRNAs is an important gene regulatory mechanism shaping the transcriptome. AtMC1 is an Arabidopsis thaliana type I metacaspase that positively regulates the hypersensitive response. Here, we found that AtMC1 is involved in the regulation of plant immunity to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and is physically associated with Sm-like4 (LSM4), which is involved in pre-mRNA splicing. AtMC1 and LSM4 protein levels both increased with their coexpression as compared with their separate expression in vivo. Like AtMC1, LSM4 negatively regulates plant immunity to P. syringae pv. tomato DC3000 infection. By RNA sequencing, AtMC1 was shown to modulate the splicing of many pre-mRNAs, including 4CL3, which is a negative regulator of plant immunity. Thus, AtMC1 plays a regulatory role in pre-mRNA splicing, which might contribute to AtMC1-mediated plant immunity.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Bacillus cereus AR156 Activates Defense Responses to Pseudomonas syringae pv. tomato in Arabidopsis thaliana Similarly to flg22.

Bacillus cereus AR156 (AR156) is a plant growth-promoting rhizobacterium capable of inducing systemic resistance to Pseudomonas syringae pv. tomato in Arabidopsis thaliana. Here, we show that, when applied to Arabidopsis leaves, AR156 acted similarly to flg22, a typical pathogen-associated molecular pattern (PAMP), in initiating PAMP-triggered immunity (PTI). AR156-elicited PTI responses included phosphorylation of MPK3 and MPK6, induction of the expression of defense-related genes PR1, FRK1, WRKY22, and WRKY29, production of reactive oxygen species, and callose deposition. Pretreatment with AR156 still significantly reduced P. syringae pv. tomato multiplication and disease severity in NahG transgenic plants and mutants sid2-2, jar1, etr1, ein2, npr1, and fls2. This suggests that AR156-induced PTI responses require neither salicylic acid, jasmonic acid, and ethylene signaling nor flagella receptor kinase FLS2, the receptor of flg22. On the other hand, AR156 and flg22 acted in concert to differentially regulate a number of AGO1-bound microRNAs that function to mediate PTI. A full-genome transcriptional profiling analysis indicated that AR156 and flg22 activated similar transcriptional programs, coregulating the expression of 117 genes; their concerted regulation of 16 genes was confirmed by real-time quantitative polymerase chain reaction analysis. These results suggest that AR156 activates basal defense responses to P. syringae pv. tomato in Arabidopsis, similarly to flg22.

Induced Systemic Resistance against Botrytis cinerea by Bacillus cereus AR156 through a JA/ET- and NPR1-Dependent Signaling Pathway and Activates PAMP-Triggered Immunity in Arabidopsis.

Induced resistance response is a potent and cost effective plant defense against pathogen attack. The effectiveness and underlying mechanisms of the suppressive ability by Bacillus cereus AR156 to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) in Arabidopsis has been investigated previously; however, the strength of induced systemic resistance (ISR) activity against Botrytis cinerea remains unknown. Here, we show that root-drench application of AR156 significantly reduces disease incidence through activation of ISR. This protection is accompanied with multilayered ISR defense response activated via enhanced accumulation of PR1 protein expression in a timely manner, hydrogen peroxide accumulation and callose deposition, which is significantly more intense in plants with both AR156 pretreatment and B. cinerea inoculation than that in plants with pathogen inoculation only. Moreover, AR156 can trigger ISR in sid2-2 and NahG mutants, but not in jar1, ein2 and npr1 mutant plants. Our results indicate that AR156-induced ISR depends on JA/ET-signaling pathway and NPR1, but not SA. Also, AR156-treated plants are able to rapidly activate MAPK signaling and FRK1/WRKY53 gene expression, both of which are involved in pathogen associated molecular pattern (PAMP)-triggered immunity (PTI). The results indicate that AR156 can induce ISR by the JA/ET-signaling pathways in an NPR1-dependent manner and involves multiple PTI components.

Profiling of small RNAs involved in plant-pathogen interactions.

Small RNA (sRNA)-mediated gene silencing is an important gene expression regulatory mechanism conserved in eukaryotes. Such sRNAs, first discovered in plants, are involved in diverse biological processes. In plants, sRNAs participate in many growth and developmental processes, such as embryo development, seed germination, flowering, hormone synthesis and distribution, and nutrient assimilation. However, the significance of sRNA in shaping the relationship between plants and their symbiotic microbes or pathogens has been underestimated. Recent progress in profiling sRNA, especially advances in next-generation sequencing technology, has revealed its extensive and complicated involvement in interactions between plants and viruses, bacteria, and fungi. In this review, we will summarize recent findings regarding sRNA in plant-pathogen interactions.