The adenylate cyclase gene MAC1 of Magnaporthe grisea controls appressorium formation and other aspects of growth and development.

Abstract

Magnaporthe grisea, the causal agent of rice blast disease, differentiates a specialized infection structure called an appressorium that is crucial for host plant penetration. Previously, it was found that cAMP regulates appressorium formation. To further understand the cellular mechanisms involved in appressorium formation, we have cloned a gene (MACl) encoding adenylate cyclase, a membrane-bound enzyme that catalyzes the production of cAMP from ATP, by using a polymerase chain reaction-based strategy. The entire gene was isolated and subcloned from a large insert bacteria1 artificial chromosome library. Sequence characterization showed that MACl has a high degree of identity with other adenylate cyclase genes from several filamentous fungi as well as yeasts. Gene deletion resulted in reduced vegetative growth, conidiation, and conidial germination. Transformants lacking MACl were unable t o form appressoria on an inductive surface and were unable t o penetrate susceptible rice leaves. m a c l -transformants were also sterile and produced no perithecia. Appressorium formation was restored in the presence of exogenous cAMP derivatives. These results confirm that cell signaling involving cAMP plays a central role in the development and pathogenicity of M. grisea.

Serial Analysis of Gene Expression (SAGE) of Magnaporthe grisea: genes involved in appressorium formation

“…MAC1 (genomic Contig No. 1.221) encodes adenylate cyclase, a membrane-bound enzyme that catalyses the production of cAMP from ATP (Choi and Dean 1997). Transformants lacking MAC1 were unable to form appressoria on an inductive surface and could not penetrate susceptible rice leaves.…”

“…Hydrophobin, secreted by the germ tube preconditions the adhesion of the germ tube tip, or hook, to the plant surface, and the corresponding gene MPG1 has been shown to be necessary for development of the mature appressorium (Talbot et al 1993). The a subunit of a trimeric G-protein (encoded by MAGB) and adenylate cyclase (encoded by MAC1) are also required for appressorium development (Liu and Dean 1997;Choi and Dean 1997), indicating essential roles for G-protein/cAMP signaling pathways in this process. CPKA, which encodes a catalytic subunit of cAMP-dependent protein kinase, is necessary for appressorial penetration (Mitchell and Dean 1995;Xu et al 1997).…”

Transformation: a tool for studying fungal pathogens of plants

“…The same procedure has also been applied to Candida albicans with similar results [84]. Though several posters at the 7 th International Congress of Plant Pathology reported its initial use on U. maydis and Pyrenophora teres [46], the potential benefit of this technique in the study of fungal plant pathogens has yet to be realized.…”

“…Employing A. tumefaciens to replace the gene increased this frequency to 71 % [53]. A number of genes in several fungal pathogens have been identified to be important for pathogenicity via targeted mutagenesis, including genes for mitogen-activated protein (MAP) kinase [47, 49 -54], ATP-binding cassette (ABC) transporter [55], heterotrimeric GTP-binding protein [48], adenylate cyclase [46] and regulating catabolite derepression [56]. The plant cuticle and cell wall are major physical barriers against fungal infection.…”

Magnaporthe oryzae MTP1 gene encodes a type III transmembrane protein involved in conidiation and conidial germination

“…In China more than 3.8×10 6 ha of rice has been exposed to this disease every year since 1990. Much has been learned of the molecular mechanisms regulating pre-and post-penetration events in the development and pathogenicity of M. oryzae, such as those involved in appressorium formation and invasion growth (Lee and Dean, 1993;Xu and Hamer, 1996;Choi and Dean, 1997;DeZwaan et al, 1999;Clergeot et al, 2001;Kim et al, 2005;Zhao et al, 2005;Veneault-Fourrey et al, 2006a;Odenbach et al, 2007). Among those known important genes, Pth11 is a plasma membrane protein that mediates appressorium differentiation in response to inductive substrate cues (DeZwaan et al, 1999).…”