Abstract
BackgroundPseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). This disease affects both foliage and pods, and is a major problem in temperate areas of the world. Although several bacterial genes have been determined as participants in pathogenesis, the overall process still remains poorly understood, mainly because the identity and function of many of the genes are largely unknown. In this work, a genomic library of P. syringae pv. phaseolicola NPS3121 was constructed and PCR amplification of individual fragments was carried out in order to print a DNA microarray. This microarray was used to identify genes that are differentially expressed when bean leaf extracts, pod extracts or apoplastic fluid were added to the growth medium.ResultsTranscription profiles show that 224 genes were differentially expressed, the majority under the effect of bean leaf extract and apoplastic fluid. Some of the induced genes were previously known to be involved in the first stages of the bacterial-plant interaction and virulence. These include genes encoding type III secretion system proteins and genes involved in cell-wall degradation, phaseolotoxin synthesis and aerobic metabolism. On the other hand, most repressed genes were found to be involved in the uptake and metabolism of iron.ConclusionThis study furthers the understanding of the mechanisms involved, responses and the metabolic adaptation that occurs during the interaction of P. syringae pv. phaseolicola with a susceptible host plant.
Highlights
Pseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.)
RNA samples from bacteria grown in M9 minimal medium and minimal medium supplemented with either bean leaf extract, apoplastic fluid or bean pod extract were labelled, mixed and used to hybridize the microarray (Figure 2 and see methods)
The differences observed between the effects of the three types of extract suggest that each plant tissue or extract type had a defined and distinctive transcriptome expression pattern, similar to observations in previous reports for Pectobacterium atrosepticum grown in minimal medium supplemented with potato tuber and stem extracts [22]
Summary
Pseudomonas syringae pv. phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). Phaseolicola is a Gram-negative plant-pathogenic bacterium that causes "halo blight" disease of beans (Phaseolus vulgaris L.). Phaseolicola NPS3121 was constructed and PCR amplification of individual fragments was carried out in order to print a DNA microarray This microarray was used to identify genes that are differentially expressed when bean leaf extracts, pod extracts or apoplastic fluid were added to the growth medium. Pseudomonas syringae is an important Gram-negative bacterium that infects a wide variety of plant species and causes disease symptoms ranging from leaf spots to stem cankers in agriculturally important crops. The hrp genes are induced in vitro when bacteria are grown in minimal medium with carbon sources such as sucrose, fructose or mannitol, low pH and a low N/C ratio [6] Minimal media with these characteristics seems to mimic some of the conditions bacteria might find within the apoplast. It has been suggested that the induction of hrp genes after contact with plant tissues could result from alterations in the nutritional status of the bacteria [2,6]
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