pH Regulates Endoglucanase Expression and Virulence of <i>Alternaria alternata</i> in Persimmon Fruit

Eshel, Dani; Miyara, Itay; Ailing, Tong; Dinoor, A.; Prusky, D.

doi:10.1094/mpmi.2002.15.8.774

Cited by 131 publications

(107 citation statements)

References 27 publications

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“…PL from the culture medium was analyzed by Western blotting. (6), and possibly other phytopathogenic fungi. The finding that pH plays a major role in regulation of pelB expression suggests that there is an ambient pH signal transduction pathway in C. gloeosporioides.…”

Section: Discussionmentioning

confidence: 99%

External pH and Nitrogen Source Affect Secretion of Pectate Lyase by Colletotrichum gloeosporioides

Drori

Kramer-Haimovich

Rollins

et al. 2003

Appl Environ Microbiol

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Accumulation of ammonia and associated tissue alkalinization predispose fruit to attack by Colletotrichumgloeosporioides. As the external pH increases from 4.0 to 6.0, pectate lyase (PL) and other extracellular proteins are secreted and accumulate. At pH 4.0 neither pelB (encoding PL) transcription nor PL secretion were detected; however, they were detected as the pH increased. Nitrogen assimilation also was required for PL secretion at pH 6.0. Both inorganic and organic nitrogen sources enhanced PL secretion at pH 6.0, but neither was sufficient for PL secretion at pH 4.0. Sequence analysis of the 5 upstream region of the pelB promoter revealed nine putative consensus binding sites for the Aspergillus transcription factor PacC. Consistent with this result, the transcript levels of pac1 (the C. gloeosporioides pacC homologue) and pelB increased in parallel as a function of pH. Our results suggest that the ambient pH and the nitrogen source are independent regulatory factors for processes linked to PL secretion and virulence of C. gloeosporioides.Colletotrichum gloeosporioides is a filamentous ascomycete phytopathogen that attacks the fruits of many hosts before and after harvest. During colonization by the pathogen ammonia accumulates in the host (14), which creates the alkaline pH environment necessary for the activities of some extracellular lyase enzymes, including pectate lyases (PLs) (3,4,26,27). PL has been implicated as a virulence factor of C. gloeosporioides in avocado fruit (29), and its expression is strongly affected by alkalinization. Thus, environmental conditions that affect PL secretion may be important virulence factors for C. gloeosporioides.The alkalinization of the tissue and the increased virulence of C. gloeosporioides also may depend on the availability of exogenous nitrogen, which can be converted to NH 4 ϩ . The increase in the amount of NH 4 ϩ thus increases the external pH, which leads to expression of different genes, including pelB, the gene encoding PL, and other genes encoding secreted pectolytic enzymes. In Aspergillus nidulans and Sclerotinia sclerotiorum an ambient-pH-sensing signal transduction pathway affects expression of genes encoding several secreted and outer-membrane-bound proteins, as well as enzymes that synthesize exportable metabolites (2,5,7,8,11,17,19,24). The product of the pacC gene is the terminal component of the pH signaling pathway and the transcription regulator of pH-dependent gene expression (2). This protein has a zinc finger DNA-binding domain with the core DNA consensus binding site 5Ј-GCCARG-3Ј (24).In this study our main objective was to determine the importance of the nitrogen source and the external pH in secretion of the virulence factor PL with respect to the ambient pH transcriptional regulator pacC. We hypothesized that nitrogen source availability and the ambient pH are two independent signals for transcriptional regulation of genes required for the disease processes of C. gloeosporioides and possibly other pathogens. MATERIALS AND METHODSStrai...

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Section: Discussionmentioning

confidence: 99%

External pH and Nitrogen Source Affect Secretion of Pectate Lyase by Colletotrichum gloeosporioides

Drori

Kramer-Haimovich

Rollins

et al. 2003

Appl Environ Microbiol

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“…Previous studies suggested the involvement of endo-and exoglucanases in pathogenicity and a correlation between enzyme production and symptom development during the interaction between A. alternata and its host plants (Eshel et al, 2002a). Eshel et al (2002b) demonstrated that the production of endoglucanases in A. alternata was triggered by a pathogen-induced pH increase on the host. Correlationstudies between enzyme production and symptom development suggested that endo-and exo-glucanases were involved in A. alternata pathogenicity (Eshel et al, 2000(Eshel et al, , 2002a(Eshel et al, , 2002b.…”

Section: Open Accessmentioning

confidence: 99%

“…Eshel et al (2002b) demonstrated that the production of endoglucanases in A. alternata was triggered by a pathogen-induced pH increase on the host. Correlationstudies between enzyme production and symptom development suggested that endo-and exo-glucanases were involved in A. alternata pathogenicity (Eshel et al, 2000(Eshel et al, , 2002a(Eshel et al, , 2002b. Enzymatic processes in Alternaria infections are essentially similar to those in other diseases.…”

Section: Open Accessmentioning

confidence: 99%

“…Identification of Alternaria alternata as a Causal Agent for Leaf Blight in Syringa Species 121 chemically diverse secondary metabolites are employed by fungal invaders during pathogenesis and are not required for normal growth or reproduction (Eshel et al, 2000(Eshel et al, , 2002a(Eshel et al, , 2002b. The secondary metabolites enable the fungus to degrade different types of cell wall polymers, such as cellulose, hemicellulose, and pectin (Walton, 2000).…”

Section: Open Accessmentioning

confidence: 99%

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Identification of Alternaria alternata as a Causal Agent for Leaf Blight in Syringa Species

Mmbaga¹,

Shi²,

Kim³

2011

The Plant Pathology Journal

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While many isolates of Alternaria alternata are common saprophytes on trees and shrubs, this study clearly demonstrated that A. alternata is a primary pathogen in lilac (Syringa sp.), causing a leaf-blight that affects different Syringa species. Isolates of Alternaria sp. were collected from leaf blight samples of lilacs in the field. The internal transcribed spacer (ITS) region and morphological characterization were used to identify lilac blight pathogen. Based on 100% ITS nucleotide sequence identities to the Alternaria genus in the GenBank and morphological features, these isolates were identified as A. alternata. Disease symptoms were reproduced in lilac plants inoculated with A. alternata mycelial plugs and sprayed with a fungus-free culture filtrate, indicating that pathogenesis in lilac involves secondary metabolites or toxins. Diagnostic primers were developed to detect Alternaria sp. and A. alternata in lilac leaf blight based on ITS region and four known genes associated with pathogenesis in A. alternata: mixed-linked glucanase precursor, endopolygalacturonase, hsp70, and histone genes. The results from our study indicated A. alternata is a primary pathogen in lilac leaf blight, and these diagnostic primers can be used as a tool for the fast detection of A. alternata associated with lilac leaf blight.

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“…Especially changes in the pH, nitrogen availability, and ammonium concentrations have been suggested as a regulatory factor for colonisation of pathogenic fungi. Ammonification (the active secretion of ammonium) of the host tissue leading to an alkalinisation of the host environment has been suggested to be a key factor in the enhancement of pathogenicity of several fungi such as Alternaria and Colletotrichum (Duan et al, 2010;Eshel et al, 2002;Prusky et al, 2001). Both fungi are necrotrophic pathogens that are able to degrade cells or cell components to receive small fragments suitable for their own nutrition.…”

Section: Glufosinate Ammoniummentioning

confidence: 99%

Unexpected Side Effects of Herbicides: Modulation of Plant-Pathogen Interactions

Kortekamp¹

2011

Herbicides and Environment

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pH Regulates Endoglucanase Expression and Virulence of Alternaria alternata in Persimmon Fruit

Cited by 131 publications

References 27 publications

External pH and Nitrogen Source Affect Secretion of Pectate Lyase by Colletotrichum gloeosporioides

External pH and Nitrogen Source Affect Secretion of Pectate Lyase by Colletotrichum gloeosporioides

Identification of Alternaria alternata as a Causal Agent for Leaf Blight in Syringa Species

Unexpected Side Effects of Herbicides: Modulation of Plant-Pathogen Interactions

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