CaProDH2-mediated modulation of proline metabolism confers tolerance to Ascochyta in chickpea under drought

Drought and leaf blight caused by the fungus Ascochyta rabiei often co-occur in chickpea (Cicer arietinum)-producing areas. While the responses of chickpea to either drought or A. rabiei infection have been extensively studied, their combined effect on plant defense mechanisms is unknown. Fine modulation of stress-induced signaling pathways under combined stress is an important stress adaptation mechanism that warrants a better understanding. Here we show that drought facilitates resistance against A. rabiei infection in chickpea. The analysis of proline levels and gene expression profiling of its biosynthetic pathway under combined drought and A. rabiei infection revealed the gene encoding proline dehydrogenase (CaProDH2) as a strong candidate conferring resistance to A. rabiei infection. Transcript levels of CaProDH2, pyrroline-5-carboxylate (P5C) quantification, and measurement of mitochondrial reactive oxygen species (ROS) production showed that fine modulation of the proline-P5C cycle determines the observed resistance. In addition, CaProDH2-silenced plants lost basal resistance to A. rabiei infection induced by drought, while overexpression of the gene conferred higher resistance to the fungus. We suggest that the drought-induced accumulation of proline in the cytosol helps maintain cell turgor and raises mitochondrial P5C contents by a CaProDH2-mediated step, which results in ROS production that boosts plant defense responses and confers resistance to A. rabiei infection. Our findings indicate that manipulating the proline-P5C pathway may be a possible strategy for improving stress tolerance in plants suffering from combined drought and A. rabiei infection.

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The race goes on: A fall armyworm-resistant maize inbred line influences insect oral secretion elicitation activity and nullifies herbivore suppression of plant defense

10.1101/2021.05.17.444416 ◽

2021 ◽

Author(s):

Saif ul Malook ◽

Xiao-Feng Liu ◽

Wende Liu ◽

Jinfeng Qi ◽

Shaoqun Zhou

Keyword(s):

Plant Defense ◽

Host Plant ◽

Inbred Line ◽

Defense Mechanisms ◽

Molecular Mechanisms ◽

Fall Armyworm ◽

Defense Responses ◽

Feeding Preference ◽

Maize Inbred Line ◽

Oral Secretion

Fall armyworm (Spodoptera frugiperda) is an invasive lepidopteran pest with strong feeding preference towards maize (Zea mays). Its success on maize is facilitated by a suite of specialized detoxification and manipulation mechanisms that curtail host plant defense responses. In this study, we identified a Chinese maize inbred line Xi502 that was able to mount effective defense in response to fall armyworm attack. Comparative transcriptomics analyses, phytohormonal measurements, and targeted benzoxazinoid quantification consistently demonstrate significant inducible defense responses in Xi502, but not in the susceptible reference inbred line B73. In 24 hours, fall armyworm larvae feeding on B73 showed accelerated maturation-oriented transcriptomic responses and more changes in detoxification gene expression compared to their Xi502-fed sibling. Interestingly, oral secretions collected from larvae fed on B73 and Xi502 leaves demonstrated distinct elicitation activity when applied on either host genotypes, suggesting that variation in both insect oral secretion composition and host plant alleles could influence plant defense response. These results revealed host plant adaptation towards counter-defense mechanisms in a specialist insect herbivore, adding yet another layer to the evolutionary arms race between maize and fall armyworm. This could facilitate future investigation into the molecular mechanisms in this globally important crop-pest interaction system.

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Sm1, a Proteinaceous Elicitor Secreted by the Biocontrol Fungus Trichoderma virens Induces Plant Defense Responses and Systemic Resistance

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-19-0838 ◽

2006 ◽

Vol 19 (8) ◽

pp. 838-853 ◽

Cited By ~ 217

Author(s):

Slavica Djonović ◽

Maria J. Pozo ◽

Lawrence J. Dangott ◽

Charles R. Howell ◽

Charles M. Kenerley

Keyword(s):

Plant Defense ◽

Defense Mechanisms ◽

Molecular Mechanisms ◽

Pathogenic Fungi ◽

Defense Responses ◽

Systemic Resistance ◽

Trichoderma Virens ◽

Trichoderma Spp ◽

Toxic Activity ◽

Small Protein

The soilborne filamentous fungus Trichoderma virens is a biocontrol agent with a well-known ability to produce antibiotics, parasitize pathogenic fungi, and induce systemic resistance in plants. Even though a plant-mediated response has been confirmed as a component of bioprotection by Trichoderma spp., the molecular mechanisms involved remain largely unknown. Here, we report the identification, purification, and characterization of an elicitor secreted by T. virens, a small protein designated Sm1 (small protein 1). Sm1 lacks toxic activity against plants and microbes. Instead, native, purified Sm1 triggers production of reactive oxygen species in monocot and dicot seedlings, rice, and cotton, and induces the expression of defense-related genes both locally and systemically in cotton. Gene expression analysis revealed that SM1 is expressed throughout fungal development under different nutrient conditions and in the presence of a host plant. Using an axenic hydroponic system, we show that SM1 expression and secretion of the protein is significantly higher in the presence of the plant. Pretreatment of cotton cotyledons with Sm1 provided high levels of protection to the foliar pathogen Colletotrichum sp. These results indicate that Sm1 is involved in the induction of resistance by Trichoderma spp. through the activation of plant defense mechanisms.

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Witches’ broom disease of lime contributes to phytoplasma epidemics and attracts insect vectors

Plant Disease ◽

10.1094/pdis-10-20-2112-re ◽

2020 ◽

Author(s):

Ali Masoud Al-Subhi ◽

Abdullah Mohammed Al-Sadi ◽

Rashid Al-Yahyai ◽

Yazhou Chen ◽

Thomas Mathers ◽

...

Keyword(s):

Transcription Factors ◽

Plant Defense ◽

Defense Responses ◽

Insect Vectors ◽

Plant Defense Responses ◽

Gene Encoding ◽

Axillary Branching ◽

Broom Disease ◽

Acid Lime ◽

Lime Production

An insect-transmitted phytoplasma causing Witches’ Broom Disease of Lime (WBDL) is responsible for the drastic decline in lime production in several countries. However, it is unclear how WBDL phytoplasma (WBDLp) induces witches’ broom symptoms and if these symptoms contribute to the spread of phytoplasma. Here we show that the gene encoding SAP11 of WBDLp (SAP11WBDL) is present in all WBDLp isolates collected from diseased trees. SAP11WBDL interacts with acid lime (Citrus aurantifolia) TCP transcription factors, specifically members of the TB1/CYC class that have a role in suppressing axillary branching in plants. Sampling of WBDLp-infected lime trees revealed that WBDLp titers and SAP11WBDL expression levels were higher in symptomatic leaves compared to asymptomatic sections of the same trees. Moreover, the witches’ brooms were found to attract the vector leafhopper. Defense genes that have a role in plant defense responses to bacteria and insects are more downregulated in witches’ brooms compared to asymptomatic sections of trees. These findings suggest that witches’ broom-affected parts of the trees contribute to WBDL epidemics by supporting higher phytoplasma titers and attracting insect vectors.

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Formate Dehydrogenase (FDH1) Localizes to Both Mitochondria and Chloroplast to Play a Role in Host and Nonhost Disease Resistance

10.20944/preprints202007.0272.v1 ◽

2020 ◽

Author(s):

Seonghee Lee ◽

Ramu S. Vemanna ◽

Sunhee Oh ◽

Clemencia M. Rojas ◽

Youngjae Oh ◽

...

Keyword(s):

Disease Resistance ◽

Plant Defense ◽

Formate Dehydrogenase ◽

Bacterial Pathogens ◽

Expression Patterns ◽

Defense Responses ◽

Metabolic Enzyme ◽

Marker Genes ◽

Ros Generation ◽

Basal Resistance

Nonhost disease resistance is the most common type of plant defense mechanism against potential pathogens. In this study, the metabolic enzyme formate dehydrogenase (FDH1) was identified to be involved in nonhost disease resistance in Nicotiana benthamiana and Arabidopsis thaliana. In Arabidopsis, AtFDH1 was highly upregulated in response to both host and nonhost bacterial pathogens. Arabidopsis Atfdh1 mutants were compromised in nonhost resistance, basal resistance, and gene-for-gene resistance. The expression patterns of salicylic acid (SA) and jasmonic acid (JA) marker genes after pathogen infections in Atfdh1 mutant indicated that SA is most likely involved in the FDH1-mediated plant defense response to both host and nonhost bacterial pathogens. Previous studies reported that FDH1 localizes to only mitochondria, or both mitochondria and chloroplasts. Our results showed that the AtFDH1 localized to mitochondria and the amount of FDH1 localized to mitochondria increased upon infection with host or nonhost pathogens. Interestingly, the subcellular localization of FDH1 was observed in both mitochondria and chloroplasts after infection with a nonhost pathogen in Arabidopsis. We speculate that FDH1 plays a role in cellular signaling networks between mitochondria and chloroplasts to produce coordinated defense responses such as SA-induced reactive oxygen species (ROS) generation and hypersensitive response (HR)-induced cell death against nonhost bacterial pathogens.

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Plant Defense Responses to Biotic Stress and Its Interplay With Fluctuating Dark/Light Conditions

Frontiers in Plant Science ◽

10.3389/fpls.2021.631810 ◽

2021 ◽

Vol 12 ◽

Author(s):

Zahra Iqbal ◽

Mohammed Shariq Iqbal ◽

Abeer Hashem ◽

Elsayed Fathi Abd_Allah ◽

Mohammad Israil Ansari

Keyword(s):

Plant Defense ◽

Biotic Stress ◽

Defense Mechanisms ◽

Defense Mechanism ◽

Defense Responses ◽

Light Environment ◽

Microbial Pathogens ◽

Signaling Cascade ◽

Dark Light ◽

The Impact

Plants are subjected to a plethora of environmental cues that cause extreme losses to crop productivity. Due to fluctuating environmental conditions, plants encounter difficulties in attaining full genetic potential for growth and reproduction. One such environmental condition is the recurrent attack on plants by herbivores and microbial pathogens. To surmount such attacks, plants have developed a complex array of defense mechanisms. The defense mechanism can be either preformed, where toxic secondary metabolites are stored; or can be inducible, where defense is activated upon detection of an attack. Plants sense biotic stress conditions, activate the regulatory or transcriptional machinery, and eventually generate an appropriate response. Plant defense against pathogen attack is well understood, but the interplay and impact of different signals to generate defense responses against biotic stress still remain elusive. The impact of light and dark signals on biotic stress response is one such area to comprehend. Light and dark alterations not only regulate defense mechanisms impacting plant development and biochemistry but also bestow resistance against invading pathogens. The interaction between plant defense and dark/light environment activates a signaling cascade. This signaling cascade acts as a connecting link between perception of biotic stress, dark/light environment, and generation of an appropriate physiological or biochemical response. The present review highlights molecular responses arising from dark/light fluctuations vis-à-vis elicitation of defense mechanisms in plants.

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MKK4/5-MPK3/6 Cascade Regulates Agrobacterium-Mediated Transformation by Modulating Plant Immunity in Arabidopsis

Frontiers in Plant Science ◽

10.3389/fpls.2021.731690 ◽

2021 ◽

Vol 12 ◽

Author(s):

Tengfei Liu ◽

Li Cao ◽

Yuanyuan Cheng ◽

Jing Ji ◽

Yongshu Wei ◽

...

Keyword(s):

Plant Defense ◽

Early Stage ◽

Plant Immunity ◽

Defense Responses ◽

Mitogen Activated Protein Kinase ◽

Ros Production ◽

Crown Gall Disease ◽

Mitogen Activated Protein ◽

Defense Response Genes ◽

Signaling Components

Agrobacterium tumefaciens is a specialized plant pathogen that causes crown gall disease and is commonly used for Agrobacterium-mediated transformation. As a pathogen, Agrobacterium triggers plant immunity, which affects transformation. However, the signaling components and pathways in plant immunity to Agrobacterium remain elusive. We demonstrate that two Arabidopsis mitogen-activated protein kinase kinases (MAPKKs) MKK4/MKK5 and their downstream mitogen-activated protein kinases (MAPKs) MPK3/MPK6 play major roles in both Agrobacterium-triggered immunity and Agrobacterium-mediated transformation. Agrobacteria induce MPK3/MPK6 activity and the expression of plant defense response genes at a very early stage. This process is dependent on the MKK4/MKK5 function. The loss of the function of MKK4 and MKK5 or their downstream MPK3 and MPK6 abolishes plant immunity to agrobacteria and increases transformation frequency, whereas the activation of MKK4 and MKK5 enhances plant immunity and represses transformation. Global transcriptome analysis indicates that agrobacteria induce various plant defense pathways, including reactive oxygen species (ROS) production, ethylene (ET), and salicylic acid- (SA-) mediated defense responses, and that MKK4/MKK5 is essential for the induction of these pathways. The activation of MKK4 and MKK5 promotes ROS production and cell death during agrobacteria infection. Based on these results, we propose that the MKK4/5-MPK3/6 cascade is an essential signaling pathway regulating Agrobacterium-mediated transformation through the modulation of Agrobacterium-triggered plant immunity.

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A Plant Nutrient- and Microbial Protein-Based Resistance Inducer Elicits Wheat Cultivar-Dependent Resistance Against Zymoseptoria tritici

Phytopathology ◽

10.1094/phyto-03-19-0075-r ◽

2019 ◽

Vol 109 (12) ◽

pp. 2033-2045 ◽

Cited By ~ 1

Author(s):

M. Ors ◽

B. Randoux ◽

A. Siah ◽

G. Couleaud ◽

C. Maumené ◽

...

Keyword(s):

Plant Defense ◽

Defense Mechanisms ◽

Defense Responses ◽

Resistant Cultivar ◽

Septoria Tritici Blotch ◽

Septoria Tritici ◽

Manganese Sulfate ◽

Zymoseptoria Tritici ◽

Octadecanoid Pathway ◽

Resistance Induction

The induction of plant defense mechanisms by resistance inducers is an attractive and innovative alternative to reduce the use of fungicides on wheat against Zymoseptoria tritici, the responsible agent of Septoria tritici blotch (STB). Under controlled conditions, we investigated the resistance induction in three wheat cultivars with different susceptible levels to STB as a response to a treatment with a sulfur, manganese sulfate, and protein-based resistance inducer (NECTAR Céréales). While no direct antigermination effect of the product was observed in planta, more than 50% reduction of both symptoms and sporulation were recorded on the three tested cultivars. However, an impact of the wheat genotype on resistance induction was highlighted, which affects host penetration, cell colonization, and the production of cell-wall degrading enzymes by the fungus. Moreover, in the most susceptible cultivar Alixan, the product upregulated POX2, PAL, PR1, and GLUC gene expression in both noninoculated and inoculated plants and CHIT2 in noninoculated plants only. In contrast, defense responses induced in Altigo, the most resistant cultivar, seem to be more specifically mediated by the phenylpropanoid pathway in noninoculated as well as inoculated plants, since PAL and CHS were most specifically upregulated in this cultivar. In Premio, the moderate resistant cultivar, NECTAR Céréales elicits mainly the octadecanoid pathway, via LOX and AOS induction in noninoculated plants. We concluded that this complex resistance-inducing product protects wheat against Z. tritici by stimulating the cultivar-dependent plant defense mechanisms.

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