Chemoattraction of zoospores of the soybean pathogen, Phytophthora sojae, by isoflavones

Morris, Paul F.; Ward, E. W. B.

doi:10.1016/0885-5765(92)90067-6

Cited by 183 publications

(110 citation statements)

References 27 publications

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“…The tropic response of zoospores to putrescine was assessed with a capillary assay (39). The effect of exogenous polyamines on swimming longevity was assessed by incubating cells at 17°C in solutions containing various concentrations (10 M to 10 mM) of different polyamines and counting the number of swimming cells.…”

Section: Methodsmentioning

confidence: 99%

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Levels of Polyamines and Kinetic Characterization of Their Uptake in the Soybean Pathogen Phytophthora sojae

Chibucos

Morris

2006

Appl Environ Microbiol

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Polyamines are ubiquitous biologically active aliphatic cations that are at least transiently available in the soil from decaying organic matter. Our objectives in this study were to characterize polyamine uptake kinetics in Phytophthora sojae zoospores and to quantify endogenous polyamines in hyphae, zoospores, and soybean roots. Zoospores contained 10 times more free putrescine than spermidine, while hyphae contained only 4 times as much free putrescine as spermidine. Zoospores contained no conjugated putrescine, but conjugated spermidine was present. Hyphae contained both conjugated putrescine and spermidine at levels comparable to the hyphal free putrescine and spermidine levels. In soybean roots, cadaverine was the most abundant polyamine, but only putrescine efflux was detected. The selective efflux of putrescine suggests that the regulation of polyamine availability is part of the overall plant strategy to influence microbial growth in the rhizosphere. In zoospores, uptake experiments with [1,4-14 C]putrescine and [1,4-14 C]spermidine confirmed the existence of high-affinity polyamine transport for both polyamines. Putrescine uptake was reduced by high levels of exogenous spermidine, but spermidine uptake was not reduced by exogenous putrescine. These observations suggest that P. sojae zoospores express at least two high-affinity polyamine transporters, one that is spermidine specific and a second that is putrescine specific or putrescine preferential. Disruption of polyamine uptake or metabolism has major effects on a wide range of cellular activities in other organisms and has been proposed as a potential control strategy for Phytophthora. Inhibition of polyamine uptake may be a means of reducing the fitness of the zoospore along with subsequent developmental stages that precede infection.

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Section: Methodsmentioning

confidence: 99%

“…Exogenous compounds are thought to serve as signals that promote chemotaxis and encystment rather than as nutrient sources (15). Both the zoospores and the hyphae are attracted by isoflavones released from soybean roots (38,39). When a zoospore contacts a host root, it loses its flagella, secretes an adhesive mucilaginous glycoprotein, and forms a cell wall.…”

mentioning

confidence: 99%

Levels of Polyamines and Kinetic Characterization of Their Uptake in the Soybean Pathogen Phytophthora sojae

Chibucos

Morris

2006

Appl Environ Microbiol

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“…Chemotaxis to a host-specific signal has been described for several plant-microbe associations (11,43,44). In plant-pathogenic Agrobacterium species, for example, chemotaxis to plant exudates appears to enhance virulence on soil-grown plants (24).…”

mentioning

confidence: 99%

A Phytophthora sojae G-Protein α Subunit Is Involved in Chemotaxis to Soybean Isoflavones

et al. 2008

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For the soybean pathogen Phytophthora sojae, chemotaxis of zoospores to isoflavones is believed to be critical for recognition of the host and for initiating infection. However, the molecular mechanisms underlying this chemotaxis are largely unknown. To investigate the role of G-protein and calcium signaling in chemotaxis, we analyzed the expression of several genes known to be involved in these pathways and selected one that was specifically expressed in sporangia and zoospores but not in mycelium. This gene, named PsGPA1, is a single-copy gene in P. sojae and encodes a G-protein ␣ subunit that shares 96% identity in amino acid sequence with that of Phytophthora infestans. To elucidate the function, expression of PsGPA1 was silenced by introducing antisense constructs into P. sojae. PsGPA1 silencing did not disturb hyphal growth or sporulation but severely affected zoospore behavior, including chemotaxis to the soybean isoflavone daidzein. Zoospore encystment and cyst germination were also altered, resulting in the inability of the PsGPA1-silenced mutants to infect soybean. In addition, the expressions of a calmodulin gene, PsCAM1, and two calcium-and calmodulin-dependent protein kinase genes, PsCMK3 and PsCMK4, were increased in the mutant zoospores, suggesting that PsGPA1 negatively regulates the calcium signaling pathways that are likely involved in zoospore chemotaxis.The ability to recognize host signals may be critical for the behavior of plant pathogens or symbionts. Chemotaxis to a host-specific signal has been described for several plant-microbe associations (11,43,44). In plant-pathogenic Agrobacterium species, for example, chemotaxis to plant exudates appears to enhance virulence on soil-grown plants (24). In nitrogen-fixing bacteria, such as Rhizobium and Bradyrhizobium species, expression of nodulation genes is induced by flavones and isoflavones (19), which are secondary metabolites present in seeds of leguminous plants and are exuded by the roots of those plants. Chemotaxis of zoospores of the oomycete pathogen Phytophthora sojae to isoflavones is believed to be an important step in the disease cycle, particularly in recognition of the host and in initiating infection (42,43). P. sojae is a devastating pathogen on soybean that causes "damping off" of seedlings and root rot on older plants. The annual loss worldwide is estimated to be $1 billion to $2 billion (49).P. sojae zoospores are specifically attracted to the isoflavones daidzein and genistein at concentrations of as low as 10 nM (43). Since zoospores of other Phytophthora spp. are not attracted to these compounds, chemotaxis may be part of the mechanism that determines host range (43). Besides motile zoospores, hyphal germ tubes of P. sojae also respond chemotropically to soybean isoflavones (42, 51). Although there are indications that calcium influx plays a role in chemotaxis (12), the signal transduction pathways governing the response of P. sojae to isoflavones are largely unknown. The first step in unraveling these pathways is identif...

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“…Oospores germinate to form mycelia under high soil moisture conditions, and this mycelium then produces sporangia and zoospores under continued or subsequent saturated soil conditions. Zoospores are attracted to soybean roots, specifically to the soybean specific root exudates daedzein and genestein (Morris and Ward, 1992). Once they reach a root, the zoospores lose their flagella, produce a cell wall (encyst), germinate, and subsequently infect root tissues.…”

Section: Disease Cyclementioning

confidence: 99%

Phytophthora root and stem rot of soybean.

Dorrance¹

2007

PHI

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Chemoattraction of zoospores of the soybean pathogen, Phytophthora sojae, by isoflavones

Cited by 183 publications

References 27 publications

Levels of Polyamines and Kinetic Characterization of Their Uptake in the Soybean Pathogen Phytophthora sojae

Levels of Polyamines and Kinetic Characterization of Their Uptake in the Soybean Pathogen Phytophthora sojae

A Phytophthora sojae G-Protein α Subunit Is Involved in Chemotaxis to Soybean Isoflavones

Phytophthora root and stem rot of soybean.

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