Regulatory Mechanisms of a Highly Pectinolytic Mutant of Penicillium occitanis and Functional Analysis of a Candidate Gene in the Plant Pathogen Fusarium oxysporum

Abstract

Penicillium occitanis is a model system for enzymatic regulation. A mutant strain exhibiting constitutive overproduction of different pectinolytic enzymes both under inducing (pectin) or repressing conditions (glucose) was previously isolated after chemical mutagenesis. In order to identify the molecular basis of this regulatory mechanism, the genomes of the wild type and the derived mutant strain were sequenced and compared, providing the first reference genome for this species. We used a phylogenomic approach to compare P. occitanis with other pectinolytic fungi and to trace expansions of gene families involved in carbohydrate degradation. Genome comparison between wild type and mutant identified seven mutations associated with predicted proteins. The most likely candidate was a mutation in a highly conserved serine residue of a conserved fungal protein containing a GAL4-like Zn2Cys6 binuclear cluster DNA-binding domain and a fungus-specific transcription factor regulatory middle homology region. To functionally characterize the role of this candidate gene, the mutation was recapitulated in the predicted orthologue Fusarium oxysporum, a vascular wilt pathogen which secretes a wide array of plant cell wall degrading enzymes, including polygalacturonases, pectate lyases, xylanases and proteases, all of which contribute to infection. However, neither the null mutant nor a mutant carrying the analogous point mutation exhibited a deregulation of pectinolytic enzymes. The availability, annotation and phylogenomic analysis of the P. occitanis genome sequence represents an important resource for understanding the evolution and biology of this species, and sets the basis for the discovery of new genes of biotechnological interest for the degradation of complex polysaccharides.

Pectinase Production by Rhizopus stolonifer A3 Isolated from Apple Peels

“…In order to successfully weaken and invade the host plant, they produce a variety of cell wall-degrading enzymes, such as amylase, cellulase, glucosidase, pectate lyase and xylanase (Sharafaddin et al, 2019;Perincherry et al, 2020). Fusarium species such as F. oxysporum (Bravo-Ruiz et al, 2017), F. proliferatum (Sharafaddin et al, 2019) and F. graminearum (Paccanaro et al, 2017) have demonstrated the ability to produce pectinase.…”

The WAK-like protein RFO1 acts as a sensor of the pectin methylation status in Arabidopsis cell walls to modulate root growth and defense

“…Once in the root vasculature, the fungi proliferate, blocking the xylem and causing wilting and, ultimately, plant death ( Bishop and Cooper, 1983 ). In their path toward the root vasculature, F. oxysporum and V. dahliae modify and degrade the plant cell walls through the secretion of a wide range of cell-wall-modifying enzymes ( Jonkers and Rep, 2009 ; Glass et al., 2013 ; Bravo-Ruiz et al., 2017 ), including PMEs, pectin and pectate lyases, and polygalacturonases ( Cooper and Wood, 1975 ; Durrands and Cooper, 1988 ; Di Pietro and Roncero, 1998 ; Huertas-González et al., 1999 ; García-Maceira et al., 2000 ; García-Maceira et al., 2001 ; Bravo Ruiz et al., 2016 ; Fan et al., 2017 ; Yang et al., 2018 ; Safran et al., 2021 ; Gámez-Arjona et al., 2022 ). It is vital for a host plant’s survival to sense these pectin modifications, either directly or through the sensing of pectin degradation products, as part of their response to these root vascular pathogens and to mediate growth-defense processes.…”