Priming Effect of Thiamine on the Enhancement of Induced Resistance to the Plant Disease Phytophthora Nicotianae in Tobacco

Abstract Induced resistance by elicitors is considered to be an eco-friendly strategy to stimulate plant defense against pathogen attack. Thiamine (vitamin B1,VB1) can act as a plant defence trigger, or priming agent, leading to a rapid counterattack on pathogen invasion.To date, the mechanisms by which VB1 provides protection against plant disease have yet to be fully elucidated, expecially no reports about VB1 treatment influenced the development of Phytophthora nicotianae in plant. Tobacco black shank (TBS) caused by P. nicotianae is destructive to almost all tobacco cultivars and is widespread in many tobacco-growing countries. In the present study, the priming effect of VB1 on tobacco against the disease P. nicotianae and its biochemical and molecular impact on plant defense mechanisms were evaluated. Base on the effect of VB1 on mycelial growth and zoospore formation, the appropriate VB1 treatment was used in protecting tobacco against P. nicotianae. For VB1 pretreatment, tobacco exhibited a significant reduction in disease severity. Consistent with the occurrence of induced resistance, the pronounced increase in H2O2 level, phenylalanine ammonia lyase (PAL) and peroxidase (POD) activities were observed. For defense reactions, VB1 promoted the increases of H2O2, SA and lignin contents. Moreover, the expressions of PR1, PR5, NPR1, PAL, CM1, H1N1 and EFE26 were induced by VB1, which also involved in defense reactions. Our findings indicate that the priming effect of VB1 may partially depend on the production of the callose deposition, H2O2 accumulation, and hormone SA production.

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Dicer-like proteins influence Arabidopsis root microbiota independent of RNA-directed DNA methylation

Microbiome ◽

10.1186/s40168-020-00966-y ◽

2021 ◽

Vol 9 (1) ◽

Author(s):

Richa Kaushal ◽

Li Peng ◽

Sunil K. Singh ◽

Mengrui Zhang ◽

Xinlian Zhang ◽

...

Keyword(s):

Dna Methylation ◽

Cell Wall ◽

Plant Defense ◽

Root Exudates ◽

Rrna Gene ◽

Epigenetic Factors ◽

Callose Deposition ◽

Arabidopsis Root ◽

Triple Mutation ◽

Root Microbiota

Abstract Background Plants are naturally associated with root microbiota, which are microbial communities influential to host fitness. Thus, it is important to understand how plants control root microbiota. Epigenetic factors regulate the readouts of genetic information and consequently many essential biological processes. However, it has been elusive whether RNA-directed DNA methylation (RdDM) affects root microbiota assembly. Results By applying 16S rRNA gene sequencing, we investigated root microbiota of Arabidopsis mutants defective in the canonical RdDM pathway, including dcl234 that harbors triple mutation in the Dicer-like proteins DCL3, DCL2, and DCL4, which produce small RNAs for RdDM. Alpha diversity analysis showed reductions in microbe richness from the soil to roots, reflecting the selectivity of plants on root-associated bacteria. The dcl234 triple mutation significantly decreases the levels of Aeromonadaceae and Pseudomonadaceae, while it increases the abundance of many other bacteria families in the root microbiota. However, mutants of the other examined key players in the canonical RdDM pathway showed similar microbiota as Col-0, indicating that the DCL proteins affect root microbiota in an RdDM-independent manner. Subsequently gene analysis by shotgun sequencing of root microbiome indicated a selective pressure on microbial resistance to plant defense in the dcl234 mutant. Consistent with the altered plant-microbe interactions, dcl234 displayed altered characters, including the mRNA and sRNA transcriptomes that jointly highlighted altered cell wall organization and up-regulated defense, the decreased cellulose and callose deposition in root xylem, and the restructured profile of root exudates that supported the alterations in gene expression and cell wall modifications. Conclusion Our findings demonstrate an important role of the DCL proteins in influencing root microbiota through integrated regulation of plant defense, cell wall compositions, and root exudates. Our results also demonstrate that the canonical RdDM is dispensable for Arabidopsis root microbiota. These findings not only establish a connection between root microbiota and plant epigenetic factors but also highlight the complexity of plant regulation of root microbiota.

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Elicitors: Their Significance and Primary Modes of Action in the Induction of Plant Defense Reactions

Plant and Cell Physiology ◽

10.1093/oxfordjournals.pcp.a078537 ◽

1993 ◽

Keyword(s):

Plant Defense ◽

Modes Of Action ◽

Defense Reactions

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Treatment with the Mycoparasite Pythium oligandrum Triggers Induction of Defense-Related Reactions in Tomato Roots When Challenged with Fusarium oxysporum f. sp. radicis-lycopersici

Phytopathology ◽

10.1094/phyto.1997.87.1.108 ◽

1997 ◽

Vol 87 (1) ◽

pp. 108-122 ◽

Cited By ~ 108

Author(s):

Nicole Benhamou ◽

Patrice Rey ◽

Mohamed Chérif ◽

John Hockenhull ◽

Yves Tirilly

Keyword(s):

Plant Defense ◽

Fusarium Oxysporum ◽

Host Cell ◽

Cell Walls ◽

Pythium Oligandrum ◽

Tomato Plants ◽

Host Cytoplasm ◽

Defense Reactions ◽

Tomato Roots ◽

Root Tissues

The influence exerted by the mycoparasite Pythium oligandrum in triggering plant defense reactions was investigated using an experimental system in which tomato plants were infected with the crown and root rot pathogen Fusarium oxysporum f. sp. radicis-lycopersici. To assess the antagonistic potential of P. oligandrum against F. oxysporum f. sp. radicis-lycopersici, the interaction between the two fungi was studied by scanning and transmission electron microscopy (SEM and TEM, respectively). SEM investigations of the interaction region between the fungi demonstrated that collapse and loss of turgor of F. oxysporum f. sp. radicis-lycopersici hyphae began soon after close contact was established with P. oligandrum. Ultrastructural observations confirmed that intimate contact between hyphae of P. oligandrum and cells of the pathogen resulted in a series of disturbances, including generalized disorganization of the host cytoplasm, retraction of the plasmalemma, and, finally, complete loss of the protoplasm. Cytochemical labeling of chitin with wheat germ agglutinin (WGA)/ovomucoid-gold complex showed that, except in the area of hyphal penetration, the chitin component of the host cell walls was structurally preserved at a time when the host cytoplasm had undergone complete disorganization. Interestingly, the same antagonistic process was observed in planta. The specific labeling patterns obtained with the exoglucanase-gold and WGA-ovomucoid-gold complexes confirmed that P. oligandrum successfully penetrated invading cells of the pathogen without causing substantial cell wall alterations, shown by the intense labeling of chitin. Cytological investigations of samples from P. oligandrum-inoculated tomato roots revealed that the fungus was able to colonize root tissues without inducing extensive cell damage. However, there was a novel finding concerning the structural alteration of the invading hyphae, evidenced by the frequent occurrence of empty fungal shells in root tissues. Pythium ingress in root tissues was associated with host metabolic changes, culminating in the elaboration of structural barriers at sites of potential fungal penetration. Striking differences in the extent of F. oxysporum f. sp. radicis-lycopersici colonization were observed between P. oligandrum-inoculated and control tomato plants. In control roots, the pathogen multiplied abundantly through much of the tissues, whereas in P. oligandrum-colonized roots pathogen growth was restricted to the outermost root tissues. This restricted pattern of pathogen colonization was accompanied by deposition of newly formed barriers beyond the infection sites. These host reactions appeared to be amplified compared to those seen in nonchallenged P. oligandrum-infected plants. Most hyphae of the pathogen that penetrated the epidermis exhibited considerable changes. Wall appositions contained large amounts of callose, in addition to be infiltrated with phenolic compounds. The labeling pattern obtained with gold-complexed laccase showed that phenolics were widely distributed in Fusarium-challenged P. oligandrum-inoculated tomato roots. Such compounds accumulated in the host cell walls and intercellular spaces. The wall-bound chitin component in Fusarium hyphae colonizing P. oligandrum-inoculated roots was preserved at a time when hyphae had undergone substantial degradation. These observations provide the first convincing evidence that P. oligandrum has the potential to induce plant defense reactions in addition to acting as a mycoparasite.

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A small cysteine-rich phytotoxic protein of Phytophthora capsici functions as both plant defense elicitor and virulence factor

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-01-21-0025-r ◽

2021 ◽

Author(s):

Zi-Hui Zhang ◽

Jinghao Jin ◽

Gui-Lin Sheng ◽

Yu-Ping Xing ◽

Wang Liu ◽

...

Keyword(s):

Plant Defense ◽

Virulence Factor ◽

Phytophthora Capsici ◽

Ectopic Expression ◽

Defense Responses ◽

Phytophthora Species ◽

Plant Interactions ◽

Defense Gene Expression ◽

Callose Deposition ◽

Defense Gene

Small cysteine-rich (SCR) proteins including fungal avirulence proteins play important roles in the pathogen-plant interactions. SCR protein-encoding genes have been discovered in the genomes of Phytophthora pathogens, but their functions during the pathogenesis remain obscure. Here, we report the characterization of one Phytophthora capsici SCR protein, namely SCR82 with similarity to Phytophthora cactorum phytotoxic protein PcF. The scr82 gene has 10 allelic sequences in the P. capsici population. Homologues of SCR82 were not identified in fungi or other organisms but in Phytophthora relative species. Initially scr82 was weakly expressed during the mycelium, sporangium and zoospore stages, but quickly upregulated when the infection initiated. Both ectopic expression of SCR82 and recombinant yeast-expressed protein (rSCR82) caused cell death on tomato leaves. Upon treatment, rSCR82 induced plant defense responses including the induction of defense gene expression, reactive oxygen species burst and callose deposition. Knockout of scr82 in P. capsici by CRISPR/Cas9 severely impaired its virulence on host plants and reduced significantly its resistance againstoxidative stress. Inversely, its overexpression increased the pathogen’s virulence and tolerance to oxidative stress. Our results collectively demonstrate that SCR82 functions as both an important virulence factor and plant defense elicitor, which is conserved across Phytophthora species.

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