64
4.7 Role of Siderophores in Fungal Virulence
A strong competition for iron between the host and fungi may establish during fungal infection, consequently, fungi have developed specialized systems to scavenge
iron from the host by taking up hemes or glycoproteins associated in iron transport,
such as transferrin and lactoferrin. In addition, siderophores are able to compete for
iron directly due to their high affinity for this element (Caza and Kronstad 2013).
For instance, in fungus Aspergillus fumigatus, both intracellular and extracellular
siderophores are responsible for virulence.
Siderophores of phytopatogenic fungi are able to multiply in the host and promote infection (Haas et al. 2008). Oide et al. (2006) reported that, in four ascomycete species, Cochliobolus miyabeanus, C. heterostrophus, Fusarium graminearum,
and Alternaria brassicicola, siderophores are essential for resistance to hydrogen
peroxide and for full pathogenicity in their respective hosts, maize, rice, wheat, and
Arabidopsis thaliana (Oide et al. 2006).
More recently, the secretion of siderophores by pathogenic hemibiotrophic fungus Colletotrichum graminicola in maize was reported to be required for its virulence and resistance to oxidative stress (Albarouki et al. 2014). Virulence of the
pathogenic fungus A. alternata on citrus is compromised in a siderophore-deficient
fungal mutant (Chen et al. 2013). Similarly, in apple, fire blight–causing agent
Erwinia amylovora takes advantage of its siderophore DFO to infect apple seedlings and flowers and for its resistance to hydrogen peroxide.
The biosynthesis of siderophores is regulated by well-characterized transcription
factors in fungi and bacteria (Haas et al. 2008; Troxell and Hassan 2013). These transcription factors detect the iron status in the environment and regulate the expression
of their target genes by binding with cis-regulatory sequences. Taken together, these
studies reported that siderophores play an important role in the virulence of different
types of plant fungal pathogens. This data revealed that the pathogenic fungus can
assist the siderophore production and virulence factor during the disease process
based on the iron status of the host. However, recent advances have raised several
interesting questions about the mechanisms associated with plant siderophores.
4.8 Future Prospects
Brown rot diseases caused by Monilinia spp. causes severe losses of stone and
pome fruits every year. Due to their low pH, higher moisture content and nutrient composition fruits are susceptible to attack by pathogenic fungi, which
cause decaying or rotting and make them unfit for consumption by producing
mycotoxins. The storage period and market life of stone fruits is limited due to
post-harvest brown rot diseases. In India, this crop is mostly cultivated in the
Jammu and Kashmir region. Therefore, the present study was carried out with
the main objective to undertake for the management of the brown rot pathogen
that causes decaying in stone and pome fruits under storage conditions in the
S. Ashraf et al.
4.7 Role of Siderophores in Fungal Virulence
A strong competition for iron between the host and fungi may establish during fungal infection, consequently, fungi have developed specialized systems to scavenge
iron from the host by taking up hemes or glycoproteins associated in iron transport,
such as transferrin and lactoferrin. In addition, siderophores are able to compete for
iron directly due to their high affinity for this element (Caza and Kronstad 2013).
For instance, in fungus Aspergillus fumigatus, both intracellular and extracellular
siderophores are responsible for virulence.
Siderophores of phytopatogenic fungi are able to multiply in the host and promote infection (Haas et al. 2008). Oide et al. (2006) reported that, in four ascomycete species, Cochliobolus miyabeanus, C. heterostrophus, Fusarium graminearum,
and Alternaria brassicicola, siderophores are essential for resistance to hydrogen
peroxide and for full pathogenicity in their respective hosts, maize, rice, wheat, and
Arabidopsis thaliana (Oide et al. 2006).
More recently, the secretion of siderophores by pathogenic hemibiotrophic fungus Colletotrichum graminicola in maize was reported to be required for its virulence and resistance to oxidative stress (Albarouki et al. 2014). Virulence of the
pathogenic fungus A. alternata on citrus is compromised in a siderophore-deficient
fungal mutant (Chen et al. 2013). Similarly, in apple, fire blight–causing agent
Erwinia amylovora takes advantage of its siderophore DFO to infect apple seedlings and flowers and for its resistance to hydrogen peroxide.
The biosynthesis of siderophores is regulated by well-characterized transcription
factors in fungi and bacteria (Haas et al. 2008; Troxell and Hassan 2013). These transcription factors detect the iron status in the environment and regulate the expression
of their target genes by binding with cis-regulatory sequences. Taken together, these
studies reported that siderophores play an important role in the virulence of different
types of plant fungal pathogens. This data revealed that the pathogenic fungus can
assist the siderophore production and virulence factor during the disease process
based on the iron status of the host. However, recent advances have raised several
interesting questions about the mechanisms associated with plant siderophores.
4.8 Future Prospects
Brown rot diseases caused by Monilinia spp. causes severe losses of stone and
pome fruits every year. Due to their low pH, higher moisture content and nutrient composition fruits are susceptible to attack by pathogenic fungi, which
cause decaying or rotting and make them unfit for consumption by producing
mycotoxins. The storage period and market life of stone fruits is limited due to
post-harvest brown rot diseases. In India, this crop is mostly cultivated in the
Jammu and Kashmir region. Therefore, the present study was carried out with
the main objective to undertake for the management of the brown rot pathogen
that causes decaying in stone and pome fruits under storage conditions in the
S. Ashraf et al.