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Twilight, a Novel Circadian-Regulated Gene, Integrates Phototropism with Nutrient and Redox Homeostasis during Fungal Development.

Deng YZ, Qu Z, Naqvi NI - PLoS Pathog. (2015)

Bottom Line: The mRNA level of the transcription/repair factor TFB5, was significantly down regulated in the twl∆ mutant.Overexpression of TFB5 significantly suppressed the conidiation defects in the twl∆ mutant.Furthermore, Tfb5-GFP translocates to the nucleus during the phototropic response and under redox stress, while it failed to do so in the twl∆ mutant.

View Article: PubMed Central - PubMed

Affiliation: Temasek Life Sciences Laboratory, Department of Biological Sciences, National University of Singapore, Singapore; Guangdong Province Key Laboratory of Microbial Signals and Disease Control, College of Agronomy, South China Agricultural University, Guangzhou, China.

ABSTRACT
Phototropic regulation of circadian clock is important for environmental adaptation, organismal growth and differentiation. Light plays a critical role in fungal development and virulence. However, it is unclear what governs the intracellular metabolic response to such dark-light rhythms in fungi. Here, we describe a novel circadian-regulated Twilight (TWL) function essential for phototropic induction of asexual development and pathogenesis in the rice-blast fungus Magnaporthe oryzae. The TWL transcript oscillates during circadian cycles and peaks at subjective twilight. GFP-Twl remains acetylated and cytosolic in the dark, whereas light-induced phosphorylation (by the carbon sensor Snf1 kinase) drives it into the nucleus. The mRNA level of the transcription/repair factor TFB5, was significantly down regulated in the twl∆ mutant. Overexpression of TFB5 significantly suppressed the conidiation defects in the twl∆ mutant. Furthermore, Tfb5-GFP translocates to the nucleus during the phototropic response and under redox stress, while it failed to do so in the twl∆ mutant. Thus, we provide mechanistic insight into Twl-based regulation of nutrient and redox homeostasis in response to light during pathogen adaptation to the host milieu in the rice blast pathosystem.

No MeSH data available.


Related in: MedlinePlus

Twl facilitates redox homeostasis during M. oryzae pathogenicity.(A) Barley leaf explants were inoculated with conidia from the wild type or twlΔ. Disease symptoms were assessed after 5 days. Inoculum size (total number of conidia per droplet) is indicated accordingly. (B) Rice leaves from the susceptible cultivar IR31917 were inoculated with conidial droplets from wild type or twlΔ. Symptoms were examined at day 7 post inoculation. (C) Microscopic observation of twlΔ invasive hyphae developing in rice leaf sheath at 48 hpi, stained with 1% acid fuchsin. Mean values ± SE represent percentage of appressoria that differentiate invasive hyphae. Bar = 10 μm. For GSH treatment, L-Glutathione reduced (at a final concentration of 5 mM in water) was added to conidial droplets on rice leaf sheath at 24 hpi. (D) Rice leaves from 3 week-old IR31917 (blast susceptible) seedlings were wounded prior to inoculation with conidial suspension from wild type or twlΔ. The blast disease symptoms were evaluated 7 days post inoculation.
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ppat.1004972.g003: Twl facilitates redox homeostasis during M. oryzae pathogenicity.(A) Barley leaf explants were inoculated with conidia from the wild type or twlΔ. Disease symptoms were assessed after 5 days. Inoculum size (total number of conidia per droplet) is indicated accordingly. (B) Rice leaves from the susceptible cultivar IR31917 were inoculated with conidial droplets from wild type or twlΔ. Symptoms were examined at day 7 post inoculation. (C) Microscopic observation of twlΔ invasive hyphae developing in rice leaf sheath at 48 hpi, stained with 1% acid fuchsin. Mean values ± SE represent percentage of appressoria that differentiate invasive hyphae. Bar = 10 μm. For GSH treatment, L-Glutathione reduced (at a final concentration of 5 mM in water) was added to conidial droplets on rice leaf sheath at 24 hpi. (D) Rice leaves from 3 week-old IR31917 (blast susceptible) seedlings were wounded prior to inoculation with conidial suspension from wild type or twlΔ. The blast disease symptoms were evaluated 7 days post inoculation.

Mentions: Barley and rice infection assays showed that the twl∆ mutant was significantly reduced in pathogenicity (Fig 3A and 3B). Microscopic observation with infected rice leaf sheath showed retarded development of twl∆ invasive hyphae, most (around 75%; p value < 0.05) of which lacked the ability to cross the host cell wall and spread from the primary infection site to the neighboring cells (48 hpi; Fig 3C). Pathogenic microbes elicit innate immunity or defense response in plants, which is manifested through rapid accumulation of reactive oxygen species (ROS) and cell death at the site of pathogen invasion [22]. We reasoned that the defective invasive growth of the twl∆ mutant might be due to its inability to suppress/tolerate ROS produced by the host. Exogenous addition of glutathione (GSH), an antioxidant, effectively facilitated invasive growth of twl∆ mutant (Fig 3C), suggesting that Twl is likely involved in regulating host-derived ROS levels in planta. Compared to the wild type, the twl∆ mutant showed increased sensitivity to oxidative stress exerted by hydrogen peroxide or menadione (Table 1). Furthermore, infection by twl∆ conidia was significantly improved upon wounding the rice leaf prior to inoculation (Fig 3D). Wounding of the host facilitates the access to host nutrients in twl∆, thus bypassing the requirement of counter-defense mechanism against host ROS and/or the host resistance response.


Twilight, a Novel Circadian-Regulated Gene, Integrates Phototropism with Nutrient and Redox Homeostasis during Fungal Development.

Deng YZ, Qu Z, Naqvi NI - PLoS Pathog. (2015)

Twl facilitates redox homeostasis during M. oryzae pathogenicity.(A) Barley leaf explants were inoculated with conidia from the wild type or twlΔ. Disease symptoms were assessed after 5 days. Inoculum size (total number of conidia per droplet) is indicated accordingly. (B) Rice leaves from the susceptible cultivar IR31917 were inoculated with conidial droplets from wild type or twlΔ. Symptoms were examined at day 7 post inoculation. (C) Microscopic observation of twlΔ invasive hyphae developing in rice leaf sheath at 48 hpi, stained with 1% acid fuchsin. Mean values ± SE represent percentage of appressoria that differentiate invasive hyphae. Bar = 10 μm. For GSH treatment, L-Glutathione reduced (at a final concentration of 5 mM in water) was added to conidial droplets on rice leaf sheath at 24 hpi. (D) Rice leaves from 3 week-old IR31917 (blast susceptible) seedlings were wounded prior to inoculation with conidial suspension from wild type or twlΔ. The blast disease symptoms were evaluated 7 days post inoculation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4478003&req=5

ppat.1004972.g003: Twl facilitates redox homeostasis during M. oryzae pathogenicity.(A) Barley leaf explants were inoculated with conidia from the wild type or twlΔ. Disease symptoms were assessed after 5 days. Inoculum size (total number of conidia per droplet) is indicated accordingly. (B) Rice leaves from the susceptible cultivar IR31917 were inoculated with conidial droplets from wild type or twlΔ. Symptoms were examined at day 7 post inoculation. (C) Microscopic observation of twlΔ invasive hyphae developing in rice leaf sheath at 48 hpi, stained with 1% acid fuchsin. Mean values ± SE represent percentage of appressoria that differentiate invasive hyphae. Bar = 10 μm. For GSH treatment, L-Glutathione reduced (at a final concentration of 5 mM in water) was added to conidial droplets on rice leaf sheath at 24 hpi. (D) Rice leaves from 3 week-old IR31917 (blast susceptible) seedlings were wounded prior to inoculation with conidial suspension from wild type or twlΔ. The blast disease symptoms were evaluated 7 days post inoculation.
Mentions: Barley and rice infection assays showed that the twl∆ mutant was significantly reduced in pathogenicity (Fig 3A and 3B). Microscopic observation with infected rice leaf sheath showed retarded development of twl∆ invasive hyphae, most (around 75%; p value < 0.05) of which lacked the ability to cross the host cell wall and spread from the primary infection site to the neighboring cells (48 hpi; Fig 3C). Pathogenic microbes elicit innate immunity or defense response in plants, which is manifested through rapid accumulation of reactive oxygen species (ROS) and cell death at the site of pathogen invasion [22]. We reasoned that the defective invasive growth of the twl∆ mutant might be due to its inability to suppress/tolerate ROS produced by the host. Exogenous addition of glutathione (GSH), an antioxidant, effectively facilitated invasive growth of twl∆ mutant (Fig 3C), suggesting that Twl is likely involved in regulating host-derived ROS levels in planta. Compared to the wild type, the twl∆ mutant showed increased sensitivity to oxidative stress exerted by hydrogen peroxide or menadione (Table 1). Furthermore, infection by twl∆ conidia was significantly improved upon wounding the rice leaf prior to inoculation (Fig 3D). Wounding of the host facilitates the access to host nutrients in twl∆, thus bypassing the requirement of counter-defense mechanism against host ROS and/or the host resistance response.

Bottom Line: The mRNA level of the transcription/repair factor TFB5, was significantly down regulated in the twl∆ mutant.Overexpression of TFB5 significantly suppressed the conidiation defects in the twl∆ mutant.Furthermore, Tfb5-GFP translocates to the nucleus during the phototropic response and under redox stress, while it failed to do so in the twl∆ mutant.

View Article: PubMed Central - PubMed

Affiliation: Temasek Life Sciences Laboratory, Department of Biological Sciences, National University of Singapore, Singapore; Guangdong Province Key Laboratory of Microbial Signals and Disease Control, College of Agronomy, South China Agricultural University, Guangzhou, China.

ABSTRACT
Phototropic regulation of circadian clock is important for environmental adaptation, organismal growth and differentiation. Light plays a critical role in fungal development and virulence. However, it is unclear what governs the intracellular metabolic response to such dark-light rhythms in fungi. Here, we describe a novel circadian-regulated Twilight (TWL) function essential for phototropic induction of asexual development and pathogenesis in the rice-blast fungus Magnaporthe oryzae. The TWL transcript oscillates during circadian cycles and peaks at subjective twilight. GFP-Twl remains acetylated and cytosolic in the dark, whereas light-induced phosphorylation (by the carbon sensor Snf1 kinase) drives it into the nucleus. The mRNA level of the transcription/repair factor TFB5, was significantly down regulated in the twl∆ mutant. Overexpression of TFB5 significantly suppressed the conidiation defects in the twl∆ mutant. Furthermore, Tfb5-GFP translocates to the nucleus during the phototropic response and under redox stress, while it failed to do so in the twl∆ mutant. Thus, we provide mechanistic insight into Twl-based regulation of nutrient and redox homeostasis in response to light during pathogen adaptation to the host milieu in the rice blast pathosystem.

No MeSH data available.


Related in: MedlinePlus