Robin Cameron - Academia.edu (original) (raw)
Papers by Robin Cameron
Physiological and Molecular Plant Pathology
Physiological and Molecular Plant Pathology, 2021
The ability of SAR-associated molecules to induce resistance in cucumbers to Pseudomonas syringae... more The ability of SAR-associated molecules to induce resistance in cucumbers to Pseudomonas syringae pv lachrymans (lab-grown) and powdery mildew (greenhouse-grown), was investigated. Single treatments with glycerol, azelaic acid or pipecolic acid elicited modest levels of resistance in lab experiments, while single treatments with Actigard elicited high levels of resistance in both lab and greenhouse experiments. Multiple treatments with pipecolic acid elicited modest to high levels of resistance in lab-grown plants, but not in greenhouse-grown cucumber. SAR marker gene expression was observed in pipecolic acid-treated lab-grown cucumber plants. This knowledge may inform methods to protect greenhouse crops against disease.
Nature Communications
Salicylic acid (SA)-mediated innate immune responses are activated in plants perceiving volatile ... more Salicylic acid (SA)-mediated innate immune responses are activated in plants perceiving volatile monoterpenes. Here, we show that monoterpene-associated responses are propagated in feed-forward loops involving the systemic acquired resistance (SAR) signaling components pipecolic acid, glycerol-3-phosphate, and LEGUME LECTIN-LIKE PROTEIN1 (LLP1). In this cascade, LLP1 forms a key regulatory unit in both within-plant and betweenplant propagation of immunity. The data integrate molecular components of SAR into systemic signaling networks that are separate from conventional, SA-associated innate immune mechanisms. These networks are central to plant-to-plant propagation of immunity, potentially raising SAR to the population level. In this process, monoterpenes act as microbeinducible plant volatiles, which as part of plant-derived volatile blends have the potential to promote the generation of a wave of innate immune signaling within canopies or plant stands. Hence, plant-to-plant propagation of SAR holds significant potential to fortify future durable crop protection strategies following a single volatile trigger.
Physiological and Molecular Plant Pathology
Abstract The lipid transfer protein (LTP) DEFECTIVE IN INDUCED RESISTANCE1 (DIR1) is a key mobile... more Abstract The lipid transfer protein (LTP) DEFECTIVE IN INDUCED RESISTANCE1 (DIR1) is a key mobile component of the systemic acquired resistance (SAR) response. Recent evidence suggests that a DIR1-like paralog occasionally compensates for the loss of DIR1 in the dir1-1 Ws-2 mutant. Here, we demonstrate that a dir1-2 mutant in the Col-0 background is SAR-defective, while DIR1-like knockdowns are SAR-competent. Moreover, protein-protein interaction assays demonstrate that DIR1 interacts with DIR1-like and other LTPs. Further investigation of these LTPs suggests a role for LTP2 in SAR. Our results highlight the importance of multiple lipid transfer proteins for SAR in Arabidopsis .
Canadian Journal of Plant Pathology, 2016
Abstract During Systemic Acquired Resistance (SAR), a SAR-inducing infection in one leaf initiate... more Abstract During Systemic Acquired Resistance (SAR), a SAR-inducing infection in one leaf initiates movement of phloem-mobile signals to uninfected distant leaves to prime plants to respond in a resistant manner to subsequent infections. Our early work with the dir1-1 (defective in induced resistance) mutant in Arabidopsis demonstrated that the DIR1 protein is required for SAR and led to the hypothesis that DIR1, a lipid transfer protein (LTP), moves to distant leaves to activate SAR. To prove this hypothesis, we monitored DIR1-GFP accumulation in phloem exudates using an estrogen-SAR assay. In this assay, estrogen treatment induces DIR1-GFP expression in one leaf of dir1-1, followed by SAR-induction in the same leaf. DIR1-GFP was detected in exudates collected from local and distant leaves of SAR-induced plants using both DIR1 and GFP antibodies. This provides compelling evidence that DIR1 moves via the phloem to distant leaves to initiate priming. Our work fills a major gap in research on SAR as no other putative SAR mobile signal has been shown to move in planta to distant leaves. To discover how DIR1 enters the phloem, we took advantage of plant lines with compromised cell-to-cell movement caused by overexpression of Plasmodesmata-Located Proteins. These lines were defective for SAR, and DIR1 was not observed in distant leaf phloem exudates, supporting the idea that cell-to-cell movement of DIR1 through plasmodesmata is important for SAR signal movement. To discover new phloem proteins that play a role during SAR, we compared phloem exudate proteomes collected from mock- and SAR-induced leaves using quantitative LC-MS/MS. Numerous proteins were enriched in SAR-induced versus mock-induced phloem exudates and T-DNA knock-out lines in some of these genes were SAR-defective, indicating they contribute to SAR. Identification of SAR-specific phloem proteins may provide clues as to the protein complement of a high molecular weight DIR1-containing complex found in phloem exudates only after SAR induction. We will take advantage of DIR1’s proteinaceous nature to identify proteins in the high molecular weight mobile signal complex, proteins associated with phloem loading of SAR signals and proteins involved in DIR1 perception in distant leaves.
BMC Plant Biology, 2011
Background Systemic Acquired Resistance (SAR) is an induced resistance response to pathogens, cha... more Background Systemic Acquired Resistance (SAR) is an induced resistance response to pathogens, characterized by the translocation of a long-distance signal from induced leaves to distant tissues to prime them for increased resistance to future infection. DEFECTIVE in INDUCED RESISTANCE 1 (DIR1) has been hypothesized to chaperone a small signaling molecule to distant tissues during SAR in Arabidopsis. Results DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expressed in seedlings, flowers and ubiquitously in untreated or mock-inoculated mature leaf cells, including phloem sieve elements and companion cells. Inoculation of leaves with SAR-inducing avirulent or virulent Pseudomonas syringae pv tomato (Pst) resulted in Type III Secretion System-dependent suppression of DIR1 expression in leaf cells. Transient expression of fluorescent fusion proteins in tobacco and intercellular washing fluid experiments indicated that DIR1's ER signal sequence...
BMC Plant …, 2011
DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expresse... more DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expressed in seedlings, flowers and ubiquitously in untreated or mock-inoculated mature leaf cells, including phloem sieve elements and companion cells. Inoculation of leaves with ...
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](Frontiers in plant science, 2018
A corrigendum on Orthology Analysis and In Vivo Complementation Studies to Elucidate the Role of ... more A corrigendum on Orthology Analysis and In Vivo Complementation Studies to Elucidate the Role of DIR1 during Systemic Acquired Resistance in Arabidopsis thaliana and Cucumis sativus
Physiological and Molecular Plant Pathology
As Arabidopsis matures it becomes resistant to virulent Pseudomonas syringae pv. tomato (Pst), a ... more As Arabidopsis matures it becomes resistant to virulent Pseudomonas syringae pv. tomato (Pst), a defense response known as Age-Related Resistance (ARR). The contribution of two NAC transcription factors (ANAC055 and ANAC092) and jasmonic acid/ethylene (JA/ET) signaling to ARR was examined by comparing Pst growth in wild-type plants, nac mutants, an ANAC092-overexpressing line, lox2, and ein2-1. PDF1.2 expression and anac055anac092 double mutant analysis suggests that ANAC055 and ANAC092 play non-redundant roles in ARR. Additionally, ANAC092 contributes to the initiation of flowering in short day-grown plants. ANAC055 and ANAC092 expression was reduced in partially ARR-defective ein2-1 suggesting that regulation of ANAC055 and ANAC092 by EIN2 contributes to ARR.
Physiological and Molecular Plant Pathology
As plants mature it has been observed that some become more resistant to normally virulent pathog... more As plants mature it has been observed that some become more resistant to normally virulent pathogens. The ability to manifest the Age-Related Resistance (ARR) response in Arabidopsis to Pseudomonas syringae pathovars tomato (Pst) coincided with the transition to flowering in plants both delayed and accelerated in the transition to flowering. ARR was also associated with a change in PR-1 gene expression, such that young plants expressed PR-1 abundantly at 3 days post inoculation (dpi) while mature plants expressed much less. The Arabidopsis ARR response requires SA accumulation via isochorismate synthase (ICS1) [24]. ICS1 was expressed one dpi with virulent and avirulent Pst in both young and mature plants. The ARR response was also effective versus avirulent Pst providing an additional 4-fold limitation in bacterial growth. Arabidopsis ARR was found to be ineffective against two necrotrophs, Erwinia carotovora subspecies carotovora (bacterium) and Botrytis cinerea (fungus) and one obligate biotroph, Erysiphe cichoracearum (fungus). However, mature wild type, SA-deficient sid2 and NahG plants supported little growth of the obligate biotrophic oomycete, Peronospora parasitica. Therefore ARR to P. parasitica appears to be SA-independent, however the level of ARR resistance was somewhat reduced in these mutants in some experiments. Thus, there may be numerous defence pathways that contribute to adult plant resistance in Arabidopsis.
Molecular Plant-Microbe Interactions
Arabidopsis thaliana exhibits a developmentally regulated disease-resistance response known as ag... more Arabidopsis thaliana exhibits a developmentally regulated disease-resistance response known as age-related resistance (ARR), a process that requires intercellular accumulation of salicylic acid (SA), which is thought to act as an antimicrobial agent. ARR is characterized by enhanced resistance to some pathogens at the late adult-vegetative and reproductive stages. While the transition to flowering does not cause the onset of ARR, both processes involve the MADS-domain transcription factor SHORT VEGETATIVE PHASE (SVP). In this study, ARR-defective svp mutants were found to accumulate reduced levels of intercellular SA compared with wild type in response to Pseudomonas syringae pv. tomato. Double mutant and overexpression analyses suggest that SVP and SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO 1) act antagonistically, such that SVP is required for ARR to alleviate the negative effects of SOC1 on SA accumulation. In vitro, SA exhibited antibacterial and antibiofilm activity at concentrations similar to those measured in the intercellular space during ARR. In vivo, P. syringae pv. tomato formed biofilm-like aggregates in young susceptible plants, while this was drastically reduced in mature ARR-competent plants, which accumulate intercellular SA. Collectively, these results reveal a novel role for the floral regulators SVP and SOC1 in disease resistance and provide evidence that SA acts directly on pathogens as an antimicrobial agent.
Frontiers in plant science, 2016
AtDIR1 (Defective in Induced Resistance1) is an acidic lipid transfer protein essential for syste... more AtDIR1 (Defective in Induced Resistance1) is an acidic lipid transfer protein essential for systemic acquired resistance (SAR) in Arabidopsis thaliana. Upon SAR induction, DIR1 moves from locally infected to distant uninfected leaves to activate defense priming; however, a molecular function for DIR1 has not been elucidated. Bioinformatic analysis and in silico homology modeling identified putative AtDIR1 orthologs in crop species, revealing conserved protein motifs within and outside of DIR1's central hydrophobic cavity. In vitro assays to compare the capacity of recombinant AtDIR1 and targeted AtDIR1-variant proteins to bind the lipophilic probe TNS (6,P-toluidinylnaphthalene-2-sulfonate) provided evidence that conserved leucine 43 and aspartic acid 39 contribute to the size of the DIR1 hydrophobic cavity and possibly hydrophobic ligand binding. An Arabidopsis-cucumber SAR model was developed to investigate the conservation of DIR1 function in cucumber (Cucumis sativus), and w...
Frontiers in Plant Science, 2016
The plant vascular system, composed of the xylem and phloem, is important for the transport of wa... more The plant vascular system, composed of the xylem and phloem, is important for the transport of water, mineral nutrients, and photosynthate throughout the plant body. The vasculature is also the primary means by which developmental and stress signals move from one organ to another. Due to practical and technological limitations, proteomics analysis of xylem and phloem sap has been understudied in comparison to accessible sample types such as leaves and roots. However, recent advances in sample collection techniques and mass spectrometry technology are making it possible to comprehensively analyze vascular sap proteomes. In this mini-review, we discuss the emerging field of vascular sap proteomics, with a focus on recent comparative studies to identify vascular proteins that may play roles in long-distance signaling and other processes during stress responses in plants.
Physiological and Molecular Plant Pathology, 2004
As Arabidopsis plants mature, they develop age-related resistance (ARR) to virulent Pseudomonas s... more As Arabidopsis plants mature, they develop age-related resistance (ARR) to virulent Pseudomonas syringae. As for other defense responses, salicylic acid (SA) accumulation is required for ARR [Kus JV, Zaton K, Sarkar R, Cameron RK. Age-related resistance in Arabidopsis is a developmentally regulated defense response to P. syringae. Plant Cell 2002;14:479-90]. SA levels in the intercellular space increased during ARR and correlated in some experiments with anti-bacterial activity detection in intercellular washing fluids. Growth of Pseudomonas in culture was inhibited by 1 mM SA, providing support for an anti-microbial role for SA during ARR. Application of SA to the intercellular space rescued the ARR-defective mutant sid2, but not the SA-hydrolyzing transgenic line, NahG. The protection afforded by SA application in sid2 was observed only while SA levels remained elevated in the intercellular space. Destruction of SA in the intercellular space, by salicylate hydroxylase application, reduced the ARR response in wild type plants. These results strongly suggest that SA accumulation in the intercellular space is critical for manifestation of ARR.
Physiological and Molecular Plant Pathology, 2000
Plant Signaling & Behavior, 2015
S ystemic acquired resistance (SAR) is a plant defense response in which an initial localized inf... more S ystemic acquired resistance (SAR) is a plant defense response in which an initial localized infection affords enhanced pathogen resistance to distant, uninfected leaves. SAR requires efficient long-distance signaling between the infected leaf, where SAR signals are generated, and the distant uninfected leaves that receive them. A growing body of evidence indicates that the lipid transfer protein DIR1 (Defective in Induced Resistance) is an important mediator of long-distance SAR signaling. In a recent publication, we investigated if cell-to-cell movement through plasmodesmata is required for long-distance movement of DIR1 during SAR. We determined that overexpression of Plasmodesmata-Located Proteins (PDLP1 and 5) negatively impacted long-distance DIR1 movement and SAR competence, suggesting that movement through plasmodesmata contributes to long-distance signal movement during SAR.
Physiological and Molecular Plant Pathology
Physiological and Molecular Plant Pathology, 2021
The ability of SAR-associated molecules to induce resistance in cucumbers to Pseudomonas syringae... more The ability of SAR-associated molecules to induce resistance in cucumbers to Pseudomonas syringae pv lachrymans (lab-grown) and powdery mildew (greenhouse-grown), was investigated. Single treatments with glycerol, azelaic acid or pipecolic acid elicited modest levels of resistance in lab experiments, while single treatments with Actigard elicited high levels of resistance in both lab and greenhouse experiments. Multiple treatments with pipecolic acid elicited modest to high levels of resistance in lab-grown plants, but not in greenhouse-grown cucumber. SAR marker gene expression was observed in pipecolic acid-treated lab-grown cucumber plants. This knowledge may inform methods to protect greenhouse crops against disease.
Nature Communications
Salicylic acid (SA)-mediated innate immune responses are activated in plants perceiving volatile ... more Salicylic acid (SA)-mediated innate immune responses are activated in plants perceiving volatile monoterpenes. Here, we show that monoterpene-associated responses are propagated in feed-forward loops involving the systemic acquired resistance (SAR) signaling components pipecolic acid, glycerol-3-phosphate, and LEGUME LECTIN-LIKE PROTEIN1 (LLP1). In this cascade, LLP1 forms a key regulatory unit in both within-plant and betweenplant propagation of immunity. The data integrate molecular components of SAR into systemic signaling networks that are separate from conventional, SA-associated innate immune mechanisms. These networks are central to plant-to-plant propagation of immunity, potentially raising SAR to the population level. In this process, monoterpenes act as microbeinducible plant volatiles, which as part of plant-derived volatile blends have the potential to promote the generation of a wave of innate immune signaling within canopies or plant stands. Hence, plant-to-plant propagation of SAR holds significant potential to fortify future durable crop protection strategies following a single volatile trigger.
Physiological and Molecular Plant Pathology
Abstract The lipid transfer protein (LTP) DEFECTIVE IN INDUCED RESISTANCE1 (DIR1) is a key mobile... more Abstract The lipid transfer protein (LTP) DEFECTIVE IN INDUCED RESISTANCE1 (DIR1) is a key mobile component of the systemic acquired resistance (SAR) response. Recent evidence suggests that a DIR1-like paralog occasionally compensates for the loss of DIR1 in the dir1-1 Ws-2 mutant. Here, we demonstrate that a dir1-2 mutant in the Col-0 background is SAR-defective, while DIR1-like knockdowns are SAR-competent. Moreover, protein-protein interaction assays demonstrate that DIR1 interacts with DIR1-like and other LTPs. Further investigation of these LTPs suggests a role for LTP2 in SAR. Our results highlight the importance of multiple lipid transfer proteins for SAR in Arabidopsis .
Canadian Journal of Plant Pathology, 2016
Abstract During Systemic Acquired Resistance (SAR), a SAR-inducing infection in one leaf initiate... more Abstract During Systemic Acquired Resistance (SAR), a SAR-inducing infection in one leaf initiates movement of phloem-mobile signals to uninfected distant leaves to prime plants to respond in a resistant manner to subsequent infections. Our early work with the dir1-1 (defective in induced resistance) mutant in Arabidopsis demonstrated that the DIR1 protein is required for SAR and led to the hypothesis that DIR1, a lipid transfer protein (LTP), moves to distant leaves to activate SAR. To prove this hypothesis, we monitored DIR1-GFP accumulation in phloem exudates using an estrogen-SAR assay. In this assay, estrogen treatment induces DIR1-GFP expression in one leaf of dir1-1, followed by SAR-induction in the same leaf. DIR1-GFP was detected in exudates collected from local and distant leaves of SAR-induced plants using both DIR1 and GFP antibodies. This provides compelling evidence that DIR1 moves via the phloem to distant leaves to initiate priming. Our work fills a major gap in research on SAR as no other putative SAR mobile signal has been shown to move in planta to distant leaves. To discover how DIR1 enters the phloem, we took advantage of plant lines with compromised cell-to-cell movement caused by overexpression of Plasmodesmata-Located Proteins. These lines were defective for SAR, and DIR1 was not observed in distant leaf phloem exudates, supporting the idea that cell-to-cell movement of DIR1 through plasmodesmata is important for SAR signal movement. To discover new phloem proteins that play a role during SAR, we compared phloem exudate proteomes collected from mock- and SAR-induced leaves using quantitative LC-MS/MS. Numerous proteins were enriched in SAR-induced versus mock-induced phloem exudates and T-DNA knock-out lines in some of these genes were SAR-defective, indicating they contribute to SAR. Identification of SAR-specific phloem proteins may provide clues as to the protein complement of a high molecular weight DIR1-containing complex found in phloem exudates only after SAR induction. We will take advantage of DIR1’s proteinaceous nature to identify proteins in the high molecular weight mobile signal complex, proteins associated with phloem loading of SAR signals and proteins involved in DIR1 perception in distant leaves.
BMC Plant Biology, 2011
Background Systemic Acquired Resistance (SAR) is an induced resistance response to pathogens, cha... more Background Systemic Acquired Resistance (SAR) is an induced resistance response to pathogens, characterized by the translocation of a long-distance signal from induced leaves to distant tissues to prime them for increased resistance to future infection. DEFECTIVE in INDUCED RESISTANCE 1 (DIR1) has been hypothesized to chaperone a small signaling molecule to distant tissues during SAR in Arabidopsis. Results DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expressed in seedlings, flowers and ubiquitously in untreated or mock-inoculated mature leaf cells, including phloem sieve elements and companion cells. Inoculation of leaves with SAR-inducing avirulent or virulent Pseudomonas syringae pv tomato (Pst) resulted in Type III Secretion System-dependent suppression of DIR1 expression in leaf cells. Transient expression of fluorescent fusion proteins in tobacco and intercellular washing fluid experiments indicated that DIR1's ER signal sequence...
BMC Plant …, 2011
DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expresse... more DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expressed in seedlings, flowers and ubiquitously in untreated or mock-inoculated mature leaf cells, including phloem sieve elements and companion cells. Inoculation of leaves with ...
Frontiers in plant science, 2018
A corrigendum on Orthology Analysis and In Vivo Complementation Studies to Elucidate the Role of ... more A corrigendum on Orthology Analysis and In Vivo Complementation Studies to Elucidate the Role of DIR1 during Systemic Acquired Resistance in Arabidopsis thaliana and Cucumis sativus
Physiological and Molecular Plant Pathology
As Arabidopsis matures it becomes resistant to virulent Pseudomonas syringae pv. tomato (Pst), a ... more As Arabidopsis matures it becomes resistant to virulent Pseudomonas syringae pv. tomato (Pst), a defense response known as Age-Related Resistance (ARR). The contribution of two NAC transcription factors (ANAC055 and ANAC092) and jasmonic acid/ethylene (JA/ET) signaling to ARR was examined by comparing Pst growth in wild-type plants, nac mutants, an ANAC092-overexpressing line, lox2, and ein2-1. PDF1.2 expression and anac055anac092 double mutant analysis suggests that ANAC055 and ANAC092 play non-redundant roles in ARR. Additionally, ANAC092 contributes to the initiation of flowering in short day-grown plants. ANAC055 and ANAC092 expression was reduced in partially ARR-defective ein2-1 suggesting that regulation of ANAC055 and ANAC092 by EIN2 contributes to ARR.
Physiological and Molecular Plant Pathology
As plants mature it has been observed that some become more resistant to normally virulent pathog... more As plants mature it has been observed that some become more resistant to normally virulent pathogens. The ability to manifest the Age-Related Resistance (ARR) response in Arabidopsis to Pseudomonas syringae pathovars tomato (Pst) coincided with the transition to flowering in plants both delayed and accelerated in the transition to flowering. ARR was also associated with a change in PR-1 gene expression, such that young plants expressed PR-1 abundantly at 3 days post inoculation (dpi) while mature plants expressed much less. The Arabidopsis ARR response requires SA accumulation via isochorismate synthase (ICS1) [24]. ICS1 was expressed one dpi with virulent and avirulent Pst in both young and mature plants. The ARR response was also effective versus avirulent Pst providing an additional 4-fold limitation in bacterial growth. Arabidopsis ARR was found to be ineffective against two necrotrophs, Erwinia carotovora subspecies carotovora (bacterium) and Botrytis cinerea (fungus) and one obligate biotroph, Erysiphe cichoracearum (fungus). However, mature wild type, SA-deficient sid2 and NahG plants supported little growth of the obligate biotrophic oomycete, Peronospora parasitica. Therefore ARR to P. parasitica appears to be SA-independent, however the level of ARR resistance was somewhat reduced in these mutants in some experiments. Thus, there may be numerous defence pathways that contribute to adult plant resistance in Arabidopsis.
Molecular Plant-Microbe Interactions
Arabidopsis thaliana exhibits a developmentally regulated disease-resistance response known as ag... more Arabidopsis thaliana exhibits a developmentally regulated disease-resistance response known as age-related resistance (ARR), a process that requires intercellular accumulation of salicylic acid (SA), which is thought to act as an antimicrobial agent. ARR is characterized by enhanced resistance to some pathogens at the late adult-vegetative and reproductive stages. While the transition to flowering does not cause the onset of ARR, both processes involve the MADS-domain transcription factor SHORT VEGETATIVE PHASE (SVP). In this study, ARR-defective svp mutants were found to accumulate reduced levels of intercellular SA compared with wild type in response to Pseudomonas syringae pv. tomato. Double mutant and overexpression analyses suggest that SVP and SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO 1) act antagonistically, such that SVP is required for ARR to alleviate the negative effects of SOC1 on SA accumulation. In vitro, SA exhibited antibacterial and antibiofilm activity at concentrations similar to those measured in the intercellular space during ARR. In vivo, P. syringae pv. tomato formed biofilm-like aggregates in young susceptible plants, while this was drastically reduced in mature ARR-competent plants, which accumulate intercellular SA. Collectively, these results reveal a novel role for the floral regulators SVP and SOC1 in disease resistance and provide evidence that SA acts directly on pathogens as an antimicrobial agent.
Frontiers in plant science, 2016
AtDIR1 (Defective in Induced Resistance1) is an acidic lipid transfer protein essential for syste... more AtDIR1 (Defective in Induced Resistance1) is an acidic lipid transfer protein essential for systemic acquired resistance (SAR) in Arabidopsis thaliana. Upon SAR induction, DIR1 moves from locally infected to distant uninfected leaves to activate defense priming; however, a molecular function for DIR1 has not been elucidated. Bioinformatic analysis and in silico homology modeling identified putative AtDIR1 orthologs in crop species, revealing conserved protein motifs within and outside of DIR1's central hydrophobic cavity. In vitro assays to compare the capacity of recombinant AtDIR1 and targeted AtDIR1-variant proteins to bind the lipophilic probe TNS (6,P-toluidinylnaphthalene-2-sulfonate) provided evidence that conserved leucine 43 and aspartic acid 39 contribute to the size of the DIR1 hydrophobic cavity and possibly hydrophobic ligand binding. An Arabidopsis-cucumber SAR model was developed to investigate the conservation of DIR1 function in cucumber (Cucumis sativus), and w...
Frontiers in Plant Science, 2016
The plant vascular system, composed of the xylem and phloem, is important for the transport of wa... more The plant vascular system, composed of the xylem and phloem, is important for the transport of water, mineral nutrients, and photosynthate throughout the plant body. The vasculature is also the primary means by which developmental and stress signals move from one organ to another. Due to practical and technological limitations, proteomics analysis of xylem and phloem sap has been understudied in comparison to accessible sample types such as leaves and roots. However, recent advances in sample collection techniques and mass spectrometry technology are making it possible to comprehensively analyze vascular sap proteomes. In this mini-review, we discuss the emerging field of vascular sap proteomics, with a focus on recent comparative studies to identify vascular proteins that may play roles in long-distance signaling and other processes during stress responses in plants.
Physiological and Molecular Plant Pathology, 2004
As Arabidopsis plants mature, they develop age-related resistance (ARR) to virulent Pseudomonas s... more As Arabidopsis plants mature, they develop age-related resistance (ARR) to virulent Pseudomonas syringae. As for other defense responses, salicylic acid (SA) accumulation is required for ARR [Kus JV, Zaton K, Sarkar R, Cameron RK. Age-related resistance in Arabidopsis is a developmentally regulated defense response to P. syringae. Plant Cell 2002;14:479-90]. SA levels in the intercellular space increased during ARR and correlated in some experiments with anti-bacterial activity detection in intercellular washing fluids. Growth of Pseudomonas in culture was inhibited by 1 mM SA, providing support for an anti-microbial role for SA during ARR. Application of SA to the intercellular space rescued the ARR-defective mutant sid2, but not the SA-hydrolyzing transgenic line, NahG. The protection afforded by SA application in sid2 was observed only while SA levels remained elevated in the intercellular space. Destruction of SA in the intercellular space, by salicylate hydroxylase application, reduced the ARR response in wild type plants. These results strongly suggest that SA accumulation in the intercellular space is critical for manifestation of ARR.
Physiological and Molecular Plant Pathology, 2000
Plant Signaling & Behavior, 2015
S ystemic acquired resistance (SAR) is a plant defense response in which an initial localized inf... more S ystemic acquired resistance (SAR) is a plant defense response in which an initial localized infection affords enhanced pathogen resistance to distant, uninfected leaves. SAR requires efficient long-distance signaling between the infected leaf, where SAR signals are generated, and the distant uninfected leaves that receive them. A growing body of evidence indicates that the lipid transfer protein DIR1 (Defective in Induced Resistance) is an important mediator of long-distance SAR signaling. In a recent publication, we investigated if cell-to-cell movement through plasmodesmata is required for long-distance movement of DIR1 during SAR. We determined that overexpression of Plasmodesmata-Located Proteins (PDLP1 and 5) negatively impacted long-distance DIR1 movement and SAR competence, suggesting that movement through plasmodesmata contributes to long-distance signal movement during SAR.