Characterization of a unique polysaccharide monooxygenase from the plant pathogen Magnaporthe oryzae

Abstract

Blast disease in cereal plants is caused by the fungus Magnaporthe oryzae and accounts for a significant loss in food crops. At the outset of infection, expression of a putative polysaccharide monooxygenase ( Mo PMO9A) is increased. Mo PMO9A contains a catalytic domain predicted to act on cellulose and a carbohydrate-binding domain that binds chitin. A sequence similarity network of the Mo PMO9A family AA9 showed that 220 of the 223 sequences in the Mo PMO9A-containing cluster of sequences have a conserved unannotated region with no assigned function. Expression and purification of the full length and two Mo PMO9A truncations, one containing the catalytic domain and the domain of unknown function (DUF) and one with only the catalytic domain, were carried out. In contrast to other AA9 polysaccharide monooxygenases (PMOs), Mo PMO9A is not active on cellulose but showed activity on cereal-derived m ixed (1→3, 1→4)- β -D- g lucans (MBG). Moreover, the DUF is required for activity. Mo PMO9A exhibits activity consistent with C4 oxidation of the polysaccharide and can utilize either oxygen or hydrogen peroxide as a cosubstrate. It contains a predicted 3-dimensional fold characteristic of other PMOs. The DUF is predicted to form a coiled-coil with six absolutely conserved cysteines acting as a zipper between the two α-helices. Mo PMO9A substrate specificity and domain architecture are different from previously characterized AA9 PMOs. The results, including a gene ontology analysis, support a role for Mo PMO9A in MBG degradation during plant infection. Consistent with this analysis, deletion of Mo PMO9A results in reduced pathogenicity.

The disordered C-terminal tail of fungal LPMOs from phytopathogens mediates protein dimerization and impacts plant penetration

“…LPMOs are widely distributed across all domains of life, particularly abundant in bacterial and fungal communities. Recent studies have unveiled their multiple roles in different biological contexts (9), with for instance roles proposed in the cell wall remodeling of insects (10) or fungi (11), and demonstrated functions as virulence factors in pathogenic bacteria (12), viruses (13), oomycetes (14), and fungi (15).…”

Effector‐triggered susceptibility by the rice blast fungus Magnaporthe oryzae

“…2), suppressing chitin‐triggered plant immunity (Li et al ., 2020; Martinez‐D'Alto et al ., 2023). MoPMO9A contains a catalytic domain predicted to act on cellulose and a carbohydrate‐binding domain that binds chitin (Martinez‐D'Alto et al ., 2023). Interestingly, MoPMO9A is not active on cellulose but shows activity on cereal‐derived mixed (1 → 3, 1 → 4)‐β‐ d ‐glucans (MBG), which suggests it has a role in MBG degradation during rice blast infection (Martinez‐D'Alto et al ., 2023).…”

“…MoPMO9A contains a catalytic domain predicted to act on cellulose and a carbohydrate‐binding domain that binds chitin (Martinez‐D'Alto et al ., 2023). Interestingly, MoPMO9A is not active on cellulose but shows activity on cereal‐derived mixed (1 → 3, 1 → 4)‐β‐ d ‐glucans (MBG), which suggests it has a role in MBG degradation during rice blast infection (Martinez‐D'Alto et al ., 2023). MoPMO9A is secreted extracellularly and may also play a role in appressorium‐mediated plant infection by M. oryzae .…”

“…Most recently, a novel apoplastic effector protein MoAa91 ( Magnaporthe oryzae auxiliary activity protein, alternatively named MoPMO9A) was shown compete with the immune receptor chitin elicitor‐binding protein precursor (CEBiP) for chitin binding (Fig. 2), suppressing chitin‐triggered plant immunity (Li et al ., 2020; Martinez‐D'Alto et al ., 2023). MoPMO9A contains a catalytic domain predicted to act on cellulose and a carbohydrate‐binding domain that binds chitin (Martinez‐D'Alto et al ., 2023).…”

“…MoPMO9A is secreted extracellularly and may also play a role in appressorium‐mediated plant infection by M. oryzae . MoPMO9A deletion mutants show reduced virulence which may be due to CEBiP activation by fungal GlcNAc that triggers immune responses (Li et al ., 2020) and/or its function in plant cell wall disruption (Martinez‐D'Alto et al ., 2023).…”