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Spiroplasma citri, a plant pathogenic molligute: relationships with its two hosts, the plant and the leafhopper
Joseph M Bové1, Joël Renaudin, Colette Saillard
1Laboratoire de Biologie Cellulaire et Moleculaire, INRA & Universite de Bordeaux 2, BP 81 33883 Villenave d'Ornon cedex, France. jbove@bordeaux.inra.fr
Abstract:
Spiroplasma citri, the type species of the genus Spiroplasma (Spiroplasmataceae, Mollicutes), is restricted to the phloem sieve tubes and transmitted by phloem sap-feeding insects, as is characteristic of the phytopathogenic mollicutes. The spiroplasmas are the only mollicutes showing motility and helical morphology, apparently mediated by a contractile fibrillar cytoskeleton bound to the inner surface of the spiroplasmal membrane. MreB genes, which are involved in cell-shape determination, have been identified in S. citri. Identified genes of other functional groups are those involved in the transmission of S. citri by the leafhoppers and genes coding for lipoproteins, including spiralin, bound to the outer surface of the spiroplasma membrane. S. citri mutants that are unable to use fructose induce only mild and delayed symptoms. Fructose utilization by the sieve tube-restricted wild-type spiroplasmas is postulated to deprive the companion cells of fructose, thereby impairing sucrose loading into the sieve tubes.
Insights
Spiroplasma citri utilizes fructose in plant phloem, impacting sucrose transport. This mechanism is crucial for understanding Spiroplasma citri pathogenesis and transmission by insects.
Area of Science:
- Plant pathology
- Microbiology
- Insect vector biology
Background:
- Spiroplasma citri is a phloem-limited phytopathogenic mollicute.
- Spiroplasma citri exhibits unique motility and helical morphology.
- Phytopathogenic mollicutes are transmitted by phloem sap-feeding insects.
Purpose of the Study:
- To investigate the role of fructose utilization in Spiroplasma citri pathogenesis.
- To identify genes involved in Spiroplasma citri transmission and membrane structure.
- To understand the mechanism of Spiroplasma citri-induced plant disease.
Main Methods:
- Identification of MreB genes in Spiroplasma citri.
- Analysis of genes involved in insect transmission.
- Characterization of genes encoding lipoproteins like spiralin.
- Comparison of wild-type and fructose-utilization-deficient Spiroplasma citri mutants.
Main Results:
- Mutants unable to utilize fructose induced milder, delayed symptoms in host plants.
- Genes for cell shape determination (MreB) and insect transmission were identified.
- Lipoprotein genes, including spiralin, were identified on the outer membrane.
- Fructose utilization by Spiroplasma citri may impair companion cell function and sucrose loading.
Conclusions:
- Fructose metabolism is a key factor in Spiroplasma citri pathogenicity.
- Understanding Spiroplasma citri's molecular mechanisms can inform disease management strategies.
- Further research into Spiroplasma citri-host interactions is warranted.