Bradyrhizobium japonicum IRAT FA3 promotes salt tolerance through jasmonic acid priming in Arabidopsis thaliana.

BACKGROUND: Plant growth promoting rhizobacteria (PGPR), such as Bradyrhizobium japonicum IRAT FA3, are able to improve seed germination and plant growth under various biotic and abiotic stress conditions, including high salinity stress. PGPR can affect plants' responses to stress via multiple pathways which are often interconnected but were previously thought to be distinct. Although the overall impacts of PGPR on plant growth and stress tolerance have been well documented, the underlying mechanisms are not fully elucidated. This work contributes to understanding how PGPR promote abiotic stress by revealing major plant pathways triggered by B. japonicum under salt stress. RESULTS: The plant growth-promoting rhizobacterial (PGPR) strain Bradyrhizobium japonicum IRAT FA3 reduced the levels of sodium in Arabidopsis thaliana by 37.7%. B. japonicum primed plants as it stimulated an increase in jasmonates (JA) and modulated hydrogen peroxide production shortly after inoculation. B. japonicum-primed plants displayed enhanced shoot biomass, reduced lipid peroxidation and limited sodium accumulation under salt stress conditions. Q(RT)-PCR analysis of JA and abiotic stress-related gene expression in Arabidopsis plants pretreated with B. japonicum and followed by six hours of salt stress revealed differential gene expression compared to non-inoculated plants. Response to Desiccation (RD) gene RD20 and reactive oxygen species scavenging genes CAT3 and MDAR2 were up-regulated in shoots while CAT3 and RD22 were increased in roots by B. japonicum, suggesting roles for these genes in B. japonicum-mediated salt tolerance. B. japonicum also influenced reductions of RD22, MSD1, DHAR and MYC2 in shoots and DHAR, ADC2, RD20, RD29B, GTR1, ANAC055, VSP1 and VSP2 gene expression in roots under salt stress. CONCLUSION: Our data showed that MYC2 and JAR1 are required for B. japonicum-induced shoot growth in both salt stressed and non-stressed plants. The observed microbially influenced reactions to salinity stress in inoculated plants underscore the complexity of the B. japonicum jasmonic acid-mediated plant response salt tolerance.

Bradyrhizobium japonicum IRAT FA3 Alters Arabidopsis thaliana Root Architecture via Regulation of Auxin Efflux Transporters PIN2, PIN3, PIN7, and ABCB19.

Beneficial rhizobacteria can stimulate changes in plant root development. Although root system growth is mediated by multiple factors, the regulated distribution of the phytohormone auxin within root tissues plays a principal role. Auxin transport facilitators help to generate the auxin gradients and maxima that determine root structure. Here, we show that the plant-growth-promoting rhizobacterial strain Bradyrhizobium japonicum IRAT FA3 influences specific auxin efflux transporters to alter Arabidopsis thaliana root morphology. Gene expression profiling of host transcripts in control and B. japonicum-inoculated roots of the wild-type A. thaliana accession Col-0 confirmed upregulation of PIN2, PIN3, PIN7, and ABCB19 with B. japonicum and identified genes potentially contributing to a diverse array of auxin-related responses. Cocultivation of the bacterium with loss-of-function auxin efflux transport mutants revealed that B. japonicum requires PIN3, PIN7, and ABCB19 to increase lateral root development and utilizes PIN2 to reduce primary root length. Accelerated lateral root primordia production due to B. japonicum was not observed in single pin3, pin7, or abcb19 mutants, suggesting independent roles for PIN3, PIN7, and ABCB19 during the plant-microbe interaction. Our work demonstrates B. japonicum's influence over host transcriptional reprogramming during plant interaction with this beneficial microbe and the subsequent alterations to root system architecture.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A novel Arabidopsis pathosystem reveals cooperation of multiple hormonal response-pathways in host resistance against the global crop destroyer Macrophomina phaseolina.

Dubbed as a "global destroyer of crops", the soil-borne fungus Macrophomina phaseolina (Mp) infects more than 500 plant species including many economically important cash crops. Host defenses against infection by this pathogen are poorly understood. We established interactions between Mp and Arabidopsis thaliana (Arabidopsis) as a model system to quantitatively assess host factors affecting the outcome of Mp infections. Using agar plate-based infection assays with different Arabidopsis genotypes, we found signaling mechanisms dependent on the plant hormones ethylene, jasmonic acid and salicylic acid to control host defense against this pathogen. By profiling host transcripts in Mp-infected roots of the wild-type Arabidopsis accession Col-0 and ein2/jar1, an ethylene/jasmonic acid-signaling deficient mutant that exhibits enhanced susceptibility to this pathogen, we identified hundreds of genes potentially contributing to a diverse array of defense responses, which seem coordinated by complex interplay between multiple hormonal response-pathways. Our results establish Mp/Arabidopsis interactions as a useful model pathosystem, allowing for application of the vast genomics-related resources of this versatile model plant to the systematic investigation of previously understudied host defenses against a major crop plant pathogen.

The Synthetic Elicitor DPMP (2,4-dichloro-6-{(E)-[(3-methoxyphenyl)imino]methyl}phenol) Triggers Strong Immunity in Arabidopsis thaliana and Tomato.

Synthetic elicitors are drug-like compounds that are structurally distinct from natural defense elicitors. They can protect plants from diseases by activating host immune responses and can serve as tools for the dissection of the plant immune system as well as leads for the development of environmentally-safe pesticide alternatives. By high-throughput screening, we previously identified 114 synthetic elicitors that activate expression of the pathogen-responsive CaBP22(-333)::GUS reporter gene in Arabidopsis thaliana (Arabidopsis), 33 of which are [(phenylimino)methyl]phenol (PMP) derivatives or PMP-related compounds. Here we report on the characterization of one of these compounds, 2,4-dichloro-6-{(E)-[(3-methoxyphenyl)imino]methyl}phenol (DPMP). DPMP strongly triggers disease resistance of Arabidopsis against bacterial and oomycete pathogens. By mRNA-seq analysis we found transcriptional profiles triggered by DPMP to resemble typical defense-related responses.

Use of enhancer trapping to identify pathogen-induced regulatory events spatially restricted to plant-microbe interaction sites.

Plant genes differentially expressed during plant-pathogen interactions can be important for host immunity or can contribute to pathogen virulence. Large-scale transcript profiling studies, such as microarray- or mRNA-seq-based analyses, have revealed hundreds of genes that are differentially expressed during plant-pathogen interactions. However, transcriptional responses limited to a small number of cells at infection sites can be difficult to detect using these approaches, as they are under-represented in the whole-tissue datasets typically generated by such methods. This study examines the interactions between Arabidopsis thaliana (Arabidopsis) and the pathogenic oomycete Hyaloperonospora arabidopsidis (Hpa) by enhancer trapping to uncover novel plant genes involved in local infection responses. We screened a ß-glucuronidase (GUS) reporter-based enhancer-trap population for expression patterns related to Hpa infection. Several independent lines exhibited GUS expression in leaf mesophyll cells surrounding Hpa structures, indicating a regulatory response to pathogen infection. One of these lines contained a single enhancer-trap insertion in an exon of At1g08800 (MyoB1, Myosin Binding Protein 1) and was subsequently found to exhibit reduced susceptibility to Hpa. Two additional Arabidopsis lines with T-DNA insertions in exons of MyoB1 also exhibited approximately 30% fewer spores than wild-type plants. This study demonstrates that our enhancer-trapping strategy can result in the identification of functionally relevant pathogen-responsive genes. Our results further suggest that MyoB1 either positively contributes to Hpa virulence or negatively affects host immunity against this pathogen.

The Synthetic Elicitor 2-(5-Bromo-2-Hydroxy-Phenyl)-Thiazolidine-4-Carboxylic Acid Links Plant Immunity to Hormesis.

Synthetic elicitors are drug-like compounds that induce plant immune responses but are structurally distinct from natural defense elicitors. Using high-throughput screening, we previously identified 114 synthetic elicitors that activate the expression of a pathogen-responsive reporter gene in Arabidopsis (Arabidopsis thaliana). Here, we report on the characterization of one of these compounds, 2-(5-bromo-2-hydroxy-phenyl)-thiazolidine-4-carboxylic acid (BHTC). BHTC induces disease resistance of plants against bacterial, oomycete, and fungal pathogens and has a unique mode of action and structure. Surprisingly, we found that low doses of BHTC enhanced root growth in Arabidopsis, while high doses of this compound inhibited root growth, besides inducing defense. These effects are reminiscent of the hormetic response, which is characterized by low-dose stimulatory effects of a wide range of agents that are toxic or inhibitory at higher doses. Like its effects on defense, BHTC-induced hormesis in Arabidopsis roots is partially dependent on the WRKY70 transcription factor. Interestingly, BHTC-induced root hormesis is also affected in the auxin-response mutants axr1-3 and slr-1. By messenger RNA sequencing, we uncovered a dramatic difference between transcriptional profiles triggered by low and high doses of BHTC. Only high levels of BHTC induce typical defense-related transcriptional changes. Instead, low BHTC levels trigger a coordinated intercompartmental transcriptional response manifested in the suppression of photosynthesis- and respiration-related genes in the nucleus, chloroplasts, and mitochondria as well as the induction of development-related nuclear genes. Taken together, our functional characterization of BHTC links defense regulation to hormesis and provides a hypothetical transcriptional scenario for the induction of hormetic root growth.

Angiotensin II type 1 receptor-EGF receptor cross-talk regulates ureteric bud branching morphogenesis.

Angiotensinogen-, angiotensin-converting enzyme-, and angiotensin II (Ang II) type 1 receptor (AT(1)R)-deficient mice exhibit a dilated renal pelvis (hydronephrosis) and a small papilla. These abnormalities have been attributed to impaired development of the ureteral and pelvic smooth muscle. Defects in the growth and branching of the ureteric bud (UB), which gives rise to the collecting system, have not been examined carefully. This study tested the hypothesis that Ang II stimulates UB growth and branching in the intact metanephros. Immunohistochemistry demonstrated that embryonic mouse kidneys express AT(1)R in the UB and its branches. Embryonic day 11.5 metanephroi were microdissected from Hoxb7-green fluorescence protein mice and grown for 48 h in serum-free medium in the presence or absence of Ang II. The number of green fluorescence protein-positive UB branch points (BP) and tips was monitored in each explant at 24 and 48 h. Ang II increased the number of UB tips and BP at 24 h (tips: 24.3 +/- 1.1 versus 18.3 +/- 0.7, P < 0.01; BP: 14.4 +/- 0.6 versus 11.7 +/- 0.6, P < 0.01) and 48 h (tips: 30.2 +/- 1.3 versus 22.9 +/- 0.8, P < 0.01; BP: 21.3 +/- 0.9 versus 15.7 +/- 0.6, P < 0.01) compared with control. In contrast, treatment of metanephroi with the AT(1)R antagonist candesartan inhibited UB branching, decreasing the number of UB tips and BP. Similarly, inhibition of EGF receptor (EGFR) tyrosine kinase activity abrogated Ang II-stimulated UB branching. A cross-talk between the renin-angiotensin system and EGFR signaling was elicited at the cellular level by the ability of Ang II to induce tyrosine phosphorylation of EGFR in UB cells and through abrogation of Ang II-induced UB cell branching using an EGFR tyrosine kinase inhibitor. These data demonstrate that Ang II, acting via the AT(1)R, stimulates UB branching morphogenesis. This process depends on tyrosine phosphorylation of the EGFR. Cooperation of AT(1)R and EGFR signaling therefore is important in the development of the renal collecting system.

A role for angiotensin II AT1 receptors in ureteric bud cell branching.

Gene-targeting studies in mice demonstrate that the renin-angiotensin system is required for the proper development of the renal medulla. In the absence of angiotensin II (ANG II) or the ANG II type 1 (AT1) receptor, mice exhibit poor papillary development and a severe urinary-concentrating defect. These findings imply that the ureteric bud (UB) and its branches are targets for ANG II actions during renal development. However, direct evidence linking ANG II with UB-branching morphogenesis does not exist. Using immunohistochemistry, we demonstrated that UB-derived epithelia express angiotensinogen (Ao) and the AT1 receptor during murine metanephrogenesis. Ao and AT1 receptors are expressed in the UB branches and to a lesser extent in the stromal mesenchyme. AT1 receptor expression in UB-derived epithelia increased from embryo day 12 to day 16 and was observed on both luminal and basolateral membranes. In accord with these findings, cultured murine UB cells express AT1 receptor protein and mRNA. Treatment of UB cells cultured in three-dimensional type I collagen gels with ANG II (10-7 to 10-5 M) elicits a dose-related increase in the number of cells that have primary and secondary branches. These effects of ANG II on UB branching are abrogated by pretreatment with the AT1 receptor antagonist candesartan. These data demonstrate a direct and independent role for ANG II acting via AT1 receptors on UB cell branching in vitro. The presence of Ao in the stroma and AT1 on UB cells supports the notion that cross talk between stroma and epithelial cells is crucial to epithelial branching morphogenesis in the developing kidney.