The Basic Leucine Zipper Transcription Factor Moatf1 Mediates Oxidative Stress Responses and Is Necessary for Full Virulence of the Rice Blast Fungus Magnaporthe oryzae

Abstract

Magnaporthe oryzae is the causal agent of rice blast disease, leading to enormous losses of rice production. Here, we characterized a basic leucine zipper (bZIP) transcription factor, Moatf1, in M. oryzae, a homolog of Schizosaccharomyces pombe ATF/CREB that regulates the oxidative stress response. Moatf1 deletion caused retarded vegetative growth of mycelia, and the Moatf1 mutant exhibited higher sensitivity to hydrogen peroxide (H(2)O(2)) than did the wild-type strain. The mutant showed severely reduced activity of extracellular enzymes and transcription level of laccases and peroxidases and exhibited significantly reduced virulence on rice cultivar CO-39. On rice leaf sheath, most of the infectious hyphae of the mutant became swollen and displayed restricted growth in primary infected cells. Defense response was strongly activated in plants infected by the mutant. Diamino benzidine staining revealed an accumulation of H(2)O(2) around Moatf1 mutant appressoria and rice cells with Moatf1 hyphae that was absent in the wild type. Inhibition of the plant NADPH oxidase by diphenyleneiodonium prevented host-derived H(2)O(2) accumulation and restored infectious hyphal growth of the mutant in rice cells. Thus, we conclude that Moatf1 is necessary for full virulence of M. oryzae by regulating the transcription of laccases and peroxidases to impair reactive oxygen species-mediated plant defense.

N-Glycosylation of Effector Proteins by an α-1,3-Mannosyltransferase Is Required for the Rice Blast Fungus to Evade Host Innate Immunity

“…The impairment in the growth of invasive hyphae, therefore, can be attributed to ROS accumulation within plant cells due to the absence of Alg3. In addition to the Dslp1 and Dalg3 mutants, several other M. oryzae mutants have been reported to induce ROS accumulation in penetrated plant cells, including mutants disrupted in DES1 (Chi et al, 2009), ATF1 (Guo et al, 2010), AP1 (Guo et al, 2011), HYR1 (Huang et al, 2011), CHS6 , and CRC1 genes. DES1, AP1, ATF1, and HYR may be involved in ROS detoxification, because expression levels of ROS-detoxifying genes were significantly reduced in these mutants (Chi et al, 2009;Guo et al, 2010Guo et al, , 2011Huang et al, 2011;Adam et al, 2012).…”

Reactive oxygen species and plant resistance to fungal pathogens

“…They consist in non-fluorescent molecules that become fluorescent when oxidised by ROS, and the emitted fluorescence can be observed by fluorimetry and/or by fluorescent microscopy, an advantage of such probes (Benikhlef et al, 2013;Bulgakov et al, 2012;Fester and Hause, 2005;Guo et al, 2010;Kolla et al, 2007;L'Haridon et al, 2011;Li et al, 2007;Liu et al, 2010;Ma et al, 2013;Peleg-Grossman et al, 2012;Plancot et al, 2013;Tada et al, 2004;Wen et al, 2008;Ye et al, 2013). Luminol or luminol analogues are sensitive chemiluminescent probes used to quantify a relative intensity of ROS by counting the emitted light with a luminometer, CDD camera or a scintillation counter (Dubreuil-Maurizi et al, 2010;Flury et al, 2013;Kunz et al, 2006;L'Haridon et al, 2011;Mersmann et al, 2010).…”

“…Recently, the transcription factor Moatf1 homologous to the yeast ATF/CREB that regulates the oxidative stress response was identified in Magnaporthe grisea. Targeted gene deletion of Moatf results in a higher sensitivity to ROS, a reduced expression and activity of extracellular laccases and peroxidases associated with a reduced virulence on rice (Guo et al, 2010). H 2 O 2 accumulated around the appressorium in the deletion mutant but not in the wild type fungus and inhibition of the rice NADPH oxidases with diphenyleneiodonium (DPI) restored hyphal growth and virulence of the mutant (Guo et al, 2010).…”

“…Targeted gene deletion of Moatf results in a higher sensitivity to ROS, a reduced expression and activity of extracellular laccases and peroxidases associated with a reduced virulence on rice (Guo et al, 2010). H 2 O 2 accumulated around the appressorium in the deletion mutant but not in the wild type fungus and inhibition of the rice NADPH oxidases with diphenyleneiodonium (DPI) restored hyphal growth and virulence of the mutant (Guo et al, 2010). The MoHYR1 gene of M. oryzae encodes a glutathione peroxidase GSHPx domain and was shown to be part of the antioxidative defence in M. grisea, since Dhyr1 deletion mutants were impaired in tolerance to H 2 O 2 in vitro and in planta as well as in virulence (Huang et al, 2011).…”

Basic Leucine Zipper (bZIP) Domain Transcription Factor MBZ1 Regulates Cell Wall Integrity, Spore Adherence, and Virulence in Metarhizium robertsii

“…Different bZIP-type TFs have also been characterized in various filamentous fungal species, including Aspergillus nidulans (7,8), Neurospora crassa (9), and the plant pathogens Fusarium graminearum (10 -12) and Magnaporthe oryzae (13)(14)(15). Deletions and functional characterizations of these genes revealed that bZIP-type TFs are involved in mediating fungal development, sexuality, stress responses, secondary metabolisms, and especially the virulence of plant pathogens.…”