Functions and Responses of the Leaf Apoplast Under Stress

Mitigation strategies to prevent microbial contamination of crops are lacking. We tested the hypothesis that induction of plant systemic resistance by biological (ISR) and chemical (SAR) elicitors reduces endophytic colonization of leaves by Salmonella enterica serovars Senftenberg and Typhimurium. S . Senftenberg had greater endophytic fitness than S . Typhimurium in basil and lettuce. The apoplastic population sizes of serovars Senftenberg and Typhimurium in basil and lettuce, respectively, were significantly reduced approximately 10- to 100-fold by root treatment with microbial inducers of systemic resistance compared with the H 2 O treatment. Rhodotorula glutinis effected the lowest population increase of S . Typhimurium in lettuce (120-fold) and S . Senftenberg in basil leaves (60-fold) compared with the H 2 O treatment over 10 days post-inoculation. Trichoderma harzianum and Pichia guilliermondii did not have any significant effect on S . Senftenberg in the basil apoplast. The chemical elicitors acidobenzolar-S-methyl and DL-β-amino-butyric acid inhibited S . Typhimurium multiplication in the lettuce apoplast 10- and 2-fold, respectively, compared with H 2 O-treated plants. All ISR and SAR inducers applied to lettuce roots in this study increased leaf expression of the defense gene PR1 , as did Salmonella apoplastic colonization in H 2 O-treated lettuce plants. Remarkably, both acidobenzolar-S-methyl- and R. glutinis -upregulation of PR1 was repressed by the presence of Salmonella in the leaves. However, enhanced PR1 expression was sustained longer and at greater levels upon elicitor treatment than by Salmonella induction alone. These results serve as proof of concept that priming of plant immunity may provide an intrinsic hurdle against the endophytic establishment of enteric pathogens in leafy vegetables. Importance Fruit and vegetables consumed raw have become an important vehicle of foodborne illness despite a continuous effort to improve their microbial safety. Salmonella enterica has caused numerous recalls and outbreaks of infection associated with contaminated leafy vegetables. Evidence is increasing that enteric pathogens can reach the leaf apoplast where they confront plant innate immunity. Plants may be triggered for induction of their defense signaling pathways by exposure to chemical or microbial elicitors. This priming for recognition of microbes by plant defense pathways has been used to inhibit plant pathogens and limit disease. Given that current mitigation strategies are insufficient in preventing microbial contamination of produce and associated outbreaks, we investigated the effect of plant induced resistance on S. enterica colonization of the lettuce and basil leaf apoplast in order to gain a proof of concept for the use of such an intrinsic approach to inhibit human pathogens in leafy vegetables.

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Affinity-tags are removed from Cladosporium fulvum effector proteins expressed in the tomato leaf apoplast

Journal of Experimental Botany ◽

10.1093/jxb/erj044 ◽

2006 ◽

Vol 57 (3) ◽

pp. 599-608 ◽

Cited By ~ 18

Author(s):

H. Peter van Esse ◽

Bart P. H. J. Thomma ◽

John W. van 't Klooster ◽

Pierre J. G. M. de Wit

Keyword(s):

Tomato Leaf ◽

Effector Proteins ◽

Cladosporium Fulvum ◽

Affinity Tags ◽

Leaf Apoplast

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Specific hypersensitive response-associated recognition of new apoplastic effectors fromCladosporium fulvumin wild tomato

10.1101/127746 ◽

2017 ◽

Cited By ~ 1

Author(s):

Carl H. Mesarich ◽

Bilal Ökmen ◽

Hanna Rovenich ◽

Scott A. Griffiths ◽

Changchun Wang ◽

...

Keyword(s):

Hypersensitive Response ◽

Expression System ◽

Potato Virus X ◽

Cladosporium Fulvum ◽

In Planta ◽

Antimicrobial Proteins ◽

Wild Tomato ◽

Microbe Interactions ◽

Leaf Apoplast ◽

Tomato Leaf Mould

ABSTRACTTomato leaf mould disease is caused by the biotrophic fungusCladosporium fulvum. During infection,C. fulvumproduces extracellular small secreted protein (SSP) effectors that function to promote colonization of the leaf apoplast. Resistance to the disease is governed byCfimmune receptor genes that encode receptor-like proteins (RLPs). These RLPs recognize specific SSP effectors to initiate a hypersensitive response (HR) that renders the pathogen avirulent.C. fulvumstrains capable of overcoming one or more of all clonedCfgenes have now emerged. To combat these strains, newCfgenes are required. An effectoromics approach was employed to identify wild tomato accessions carrying newCfgenes. Proteomics and transcriptome sequencing were first used to identify 70 apoplasticin planta-inducedC. fulvumSSPs. Based on sequence homology, 61 of these SSPs were novel or lacked known functional domains. Seven, however, had predicted structural homology to antimicrobial proteins, suggesting a possible role in mediating antagonistic microbe−microbe interactionsin planta. Wild tomato accessions were then screened for HR-associated recognition of 41 SSPs using thePotato virus X-based transient expression system. Nine SSPs were recognized by one or more accessions, suggesting that these plants carry newCfgenes available for incorporation into cultivated tomato.

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Peroxidase activity in the leaf apoplast is a sensitive marker for Mn toxicity and Mn tolerance in Vigna unguiculata (L.) Walp

Plant Nutrition ◽

10.1007/0-306-47624-x_127 ◽

2001 ◽

pp. 264-265

Author(s):

M. Fecht ◽

P. Maier ◽

W. J. Horst

Keyword(s):

Vigna Unguiculata ◽

Peroxidase Activity ◽

Mn Toxicity ◽

Leaf Apoplast ◽

Sensitive Marker

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Mucilaginous Secretions in the Xylem and Leaf Apoplast of the Swamp Palm Mauritia flexuosa L.f. (Arecaceae)

Microscopy and Microanalysis ◽

10.1017/s1431927620001543 ◽

2020 ◽

Vol 26 (3) ◽

pp. 609-621

Author(s):

Alessandra Flávia Silveira ◽

Maria Olívia Mercadante-Simões ◽

Leonardo Monteiro Ribeiro ◽

Yule Roberta Ferreira Nunes ◽

Lucienir Pains Duarte ◽

...

Keyword(s):

Cell Wall ◽

Cell Wall Polysaccharides ◽

Anatomical Structures ◽

Carboxylate Groups ◽

Medicinal Value ◽

Mauritia Flexuosa ◽

Vessel Elements ◽

Wall Loosening ◽

Sclerenchyma Fibers ◽

Leaf Apoplast

AbstractMauritia flexuosa palms inhabit wetland environments in the dry, seasonal Brazilian savanna (Cerrado) and produce mucilaginous secretions in the stem and petiole that have a medicinal value. The present study sought to characterize the chemical natures of those secretions and to describe the anatomical structures involved in their synthesis. Chemical analyzes of the secretions, anatomical, histochemical analyses, and electron microscopy studies were performed on the roots, stipes, petioles, and leaf blades. Stipe and petiole secretions are similar, and rich in cell wall polysaccharides and pectic compounds such as rhamnose, arabinose, xylose, mannose, galactose, and glucose, which are hydrophilic largely due to their hydroxyl and carboxylate groups. Mucilaginous secretions accumulate in the lumens of vessel elements and sclerenchyma fibers of the root, stipe, petiole, and foliar veins; their synthesis involves cell wall loosening and the activities of dictyosomes. The outer faces of the cell walls of the parenchyma tissue in the mesophyll expand to form pockets that rupture and release pectocellulose substances into the intercellular spaces. The presence of mucilage in the xylem, extending from the roots to the leaf veins and continuous with the leaf apoplast, and sub-stomatal chambers suggest a strategy for plant water economy.

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