NADPH Oxidases Are Involved in Differentiation and Pathogenicity in Botrytis cinerea

Abstract

Nicotinamide adenine dinucleotide (NADPH) oxidases have been shown to be involved in various differentiation processes in fungi. We investigated the role of two NADPH oxidases in the necrotrophic phytopathogenic fungus, Botrytis cinerea. The genes bcnoxA and bcnoxB were cloned and characterized; their deduced amino acid sequences show high homology to fungal NADPH oxidases. Analyses of single and double knock-out mutants of both NADPH oxidase genes showed that both bcnoxA and bcnoxB are involved in formation of sclerotia. Both genes have a great impact on pathogenicity: whereas bcnoxB mutants showed a retarded formation of primary lesions, probably due to an impaired formation of penetration structures, bcnoxA mutants were able to penetrate host tissue in the same way as the wild type but were much slower in colonizing the host tissue. Double mutants showed an additive effect: they were aberrant in penetration and colonization of plant tissue and, therefore, almost nonpathogenic. To study the structure of the fungal Nox complex in more detail, bcnoxR (encoding a homolog of the mammalian p67(phox), a regulatory subunit of the Nox complex) was functionally characterized. The phenotype of DeltabcnoxR mutants is identical to that of DeltabcnoxAB double mutants, providing evidence that BcnoxR is involved in activation of both Bcnox enzymes.

Polarity proteins Bem1 and Cdc24 are components of the filamentous fungal NADPH oxidase complex

“…We have shown here that E. festucae NoxR, an essential regulatory component of the filamentous fungal NADPH oxidase (NoxA/ NoxB) complex (7,11,13), physically interacts with homologs of the yeast polarity establishment proteins Bem1 and Cdc24 (22). A survey of available fungal genomes revealed that genes for NoxA/ NoxB, NoxR, RacA, BemA, and Cdc24 are widely distributed within the fungal kingdom (3,15), suggesting that this group of proteins comprises an ancestral enzyme complex for ROS production.…”

“…NoxB (Nox2) is required for ascospore germination in P. anserina and N. crassa (7,10). However, in Botrytis cinerea, both NoxA and NoxB are required for formation of the multicellular sclerotial sexual structure, but are dispensable for ascospore germination (11).…”

“…In the rice blast pathogen, Magnaporthe oryzae, disruption of either nox1 (noxA) or nox2 (noxB) resulted in loss of plant pathogenicity, due to an inability of the fungus to develop a penetration peg beneath the appressorium (12). Both NoxA and NoxB are important for pathogenicity of B. cinerea, but just NoxB is required for formation of the penetration structure (11).…”

“…In the symbiotic fungus E. festucae, a noxR mutant has a similar disrupted symbiotic interaction phenotype as ΔnoxA (6,13). In B. cinerea and N. crassa, deletion of noxR (nor-1) resulted in a similar developmental phenotype to the noxA(nox1)/noxB(nox2) double mutant (7,11). Although NoxA and NoxB have distinct cellular functions, it is not yet known how NoxR regulates these two different Nox isoforms.…”

Different ROS-Scavenging Properties of Flavonoids Determine Their Abilities to Extend Shelf Life of Tomato

“…HR responses triggered by the ROS burst provide an efficient way for plants to resist biotrophic pathogens, but necrotrophic pathogens such as B. cinerea benefit from the death of host cells (Glazebrook, 2005). During infection, necrotrophic pathogens can even produce effectors to activate the ROS burst to promote pathogenesis (Kim et al, 2008;Alkan et al, 2009), and B. cinerea carries its own genes encoding NADPH oxidase whose activity is necessary for infection (Segmüller et al, 2008). Previous data showed that tomato fruit that have high anthocyanin contents can alter ROS dynamics by limiting the spread of ROS between cells during B. cinerea infection, thus suppressing lesion development .…”