Biphasic Gene Expression Changes Elicited byPhakopsora pachyrhiziin Soybean Correlate with Fungal Penetration and Haustoria Formation    

Abstract

Inoculation of soybean (Glycine max) plants with Phakopsora pachyrhizi, the causal organism of Asian soybean rust, elicits a biphasic response characterized by a burst of differential gene expression in the first 12 h. A quiescent period occurs from 24 to 48 h after inoculation, in which P. pachyrhizi continues to develop but does not elicit strong host responses, followed by a second phase of intense gene expression. To correlate soybean responses with P. pachyrhizi growth and development, we inoculated the soybean cultivar Ankur (accession PI462312), which carries the Rpp3 resistance gene, with avirulent and virulent isolates of P. pachyrhizi. The avirulent isolate Hawaii 94-1 elicits hypersensitive cell death that limits fungal growth on Ankur and results in an incompatible response, while the virulent isolate Taiwan 80-2 grows extensively, sporulates profusely, and produces a compatible reaction. Inoculated leaves were collected over a 288-h time course for microarray analysis of soybean gene expression and microscopic analysis of P. pachyrhizi growth and development. The first burst in gene expression correlated with appressorium formation and penetration of epidermal cells, while the second burst of gene expression changes followed the onset of haustoria formation in both compatible and incompatible interactions. The proliferation of haustoria coincided with the inhibition of P. pachyrhizi growth in the incompatible interaction or the beginning of accelerated growth in the compatible interaction. The temporal relationships between P. pachyrhizi growth and host responses provide an important context in which to view interacting gene networks that mediate the outcomes of their interactions.

Transcriptome analyses and virus induced gene silencing identify genes in the Rpp4-mediated Asian soybean rust resistance pathway

“…As in the case of the Rpp2 experiments (van de Mortel et al 2007), P. pachyrhizi elicits a biphasic response characterised by a burst of differential gene expression in the first 12 hai, correlated with fungal appressorium formation and penetration of epidermal cells (Schneider et al 2011). A quiescent period occurs from 24 to 48 hai, in which P. pachyrhizi continued to develop but did not elicit strong host responses, followed by a second phase of intense defence gene expression.…”

“…Recently, our group used microarray analyses and microscopy to characterise resistance and susceptibility to P. pachyrhizi in PI462312 (Rpp3, Schneider et al 2011). As in the case of the Rpp2 experiments (van de Mortel et al 2007), P. pachyrhizi elicits a biphasic response characterised by a burst of differential gene expression in the first 12 hai, correlated with fungal appressorium formation and penetration of epidermal cells (Schneider et al 2011).…”

“…To differentiate between basal and R-gene mediated defence responses, microarray analysis was used to compare gene expression in Rpp4-silenced and mock-silenced plants. In addition, we compared these data with the Rpp2 and Rpp3 microarray data developed by our group (van de Mortel et al 2007;Schneider et al 2011) to identify transcription factors associated with multiple R-gene mediated pathways.…”

The Lesion Simulating Disease (LSD) gene family as a variable in soybean response to Phakopsora pachyrhizi infection and dehydration

“…The first peak in this response, which occurs within the first 12 hpi, is related to basal defense and is a non-specific modulation that is transient or is suppressed when the early steps in colonization are completed in both the susceptible and the resistant genotypes (van de Mortel et al 2007). A second peak in gene expression occurs early in resistant genotypes, approximately 72 hpi, while in susceptible genotypes, the response is later and continuing unaltered until 96 hpi and allows rapid fungal growth (van de Mortel et al 2007;Schneider et al 2011). Our data suggest that GmLSD1, GmLSD2, GmLSD4, GmLSD5, and GmLSD8 may be involved in the basal response because their expression was modulated at early time points and returned to levels similar to those of mock-treated controls after 48 hpi (Fig.…”

“…5). Plant tissues were sampled at a series of time-points that comprised the plant basal response (in which the first peak of plant gene expression occurs), fungal appressorium formation and epidermal cell penetration (until 12 hpi), the quiescent period between 24 and 48 hpi (when the fungus proceeds the early infection processes but does not cause strong differential gene expression in the plant) and the time-point (usually after 72 hpi) at which a second round of gene expression can occur in the plant due to fungal colonization or the formation of lesions or uredinia (van de Mortel et al 2007;Schneider et al 2011). …”