146
Extracellular siderophores are crucial for maintaining mutualistic relationship
with plants; for instance, interaction of fungi, Epichloe festucae, with ryegrass
showed symbiotic relationship, as well as to improve the sensitivity of plant’s oxidative stress (Johnson et al. 2013). More such fungal extracellular siderophores like
coprogens from Cochliobolus heterostrophus and Magnaporthe grisea and triacetylfusarinine C from Aspergillus nidulans and A. fumigatus were identified (Lee
et al. 2005; Oide et al. 2006).
Further, siderophores gained more importance since pathogenic fungus with
impaired siderophore synthesis has less lethality and reduced virulence (Haas et al.
2008) as in human pathogen A. fumigatus was shown to be affected with the survival
rate (Schrettl and Haas 2011). Therefore targeting siderophore biosynthesis renders
a greater opportunity to combat fungal infection in both human and plants. The
AmcA deficiency (a putative mitochondrial transporter protein AmcA) in A. fumigatus reduced the siderophore production where cellular polyamine content reduction was observed and the precursor ornithine usage was prioritized at cellular level
instead of taking part in siderophore biosynthesis. This increases the organism’s
susceptibility toward the drug eflornithine to affect polyamine biosynthesis
(Schafferer et al. 2015). Mutating the genes of fungal siderophore synthesis
increased sensitivity of fungal strains toward the ROS toxicity produced by plants
as a response of fungal colonization. Chen et al. (2014) observed that fungal proteins (NADPH oxidase, the redox-responsive transcription factor, mitogen-activated
protein kinase) involved in host ROS resistance are interlinked with the expression
of genes responsible for biosynthesis of siderophores. However, the knowledge
about underlying mechanisms related to oxidative stress, iron homeostasis, and fungal pathogenesis are unrevealed.
The siderophore-associated mechanisms of immunity manipulation in plants
show the involvement of siderophore groups like carboxylate (achromobactin,
citrate), hydroxamate (desferrioxamine E, ferrichrome), catecholate (enterobactin,
chrysobactin), phenolate (pyochelin, yersiniabactin), and mixed type (aerobactin
and pyoverdin) (Aznar and Dellagi (2015). The phytopathogenic ascomycetes
Cochliobolus miyabeanus, C. heterostrophus, F. graminearum, and Alternaria brassicicola required the siderophores to resist the activity of hydrogen peroxide in their
respective host’s maize, rice, wheat, and Arabidopsis thaliana (Oide et al. 2006).
The same has been observed in the hemibiotrophic fungus Colletotrichum graminicola (Albarouki et al. 2014) and A. alternata (the causative agent of infection in
citrus) (Chen et al. 2013) ,and the siderophore desferrioxamine renders support in
the fire blight-causing agent Erwinia amylovora by facilitating the infection on
apple seedlings and flowers (Dellagi et al. 1998).
The defense strategies in the case of plants which included phosphorylation
events, reactive oxygen species (ROS) accumulation, cell wall rigidification,
increased deposition of callose, upregulated genes of pathogenesis-related proteins,
and, even more, the induced systemic resistance (ISR) on any disturbance for its
stoichiometric balance of metal homeostasis are reported (Aznar and Dellagi 2015).
The mechanism of immunity induction by siderophores varies among the plant
S. Manoharan et al.
Extracellular siderophores are crucial for maintaining mutualistic relationship
with plants; for instance, interaction of fungi, Epichloe festucae, with ryegrass
showed symbiotic relationship, as well as to improve the sensitivity of plant’s oxidative stress (Johnson et al. 2013). More such fungal extracellular siderophores like
coprogens from Cochliobolus heterostrophus and Magnaporthe grisea and triacetylfusarinine C from Aspergillus nidulans and A. fumigatus were identified (Lee
et al. 2005; Oide et al. 2006).
Further, siderophores gained more importance since pathogenic fungus with
impaired siderophore synthesis has less lethality and reduced virulence (Haas et al.
2008) as in human pathogen A. fumigatus was shown to be affected with the survival
rate (Schrettl and Haas 2011). Therefore targeting siderophore biosynthesis renders
a greater opportunity to combat fungal infection in both human and plants. The
AmcA deficiency (a putative mitochondrial transporter protein AmcA) in A. fumigatus reduced the siderophore production where cellular polyamine content reduction was observed and the precursor ornithine usage was prioritized at cellular level
instead of taking part in siderophore biosynthesis. This increases the organism’s
susceptibility toward the drug eflornithine to affect polyamine biosynthesis
(Schafferer et al. 2015). Mutating the genes of fungal siderophore synthesis
increased sensitivity of fungal strains toward the ROS toxicity produced by plants
as a response of fungal colonization. Chen et al. (2014) observed that fungal proteins (NADPH oxidase, the redox-responsive transcription factor, mitogen-activated
protein kinase) involved in host ROS resistance are interlinked with the expression
of genes responsible for biosynthesis of siderophores. However, the knowledge
about underlying mechanisms related to oxidative stress, iron homeostasis, and fungal pathogenesis are unrevealed.
The siderophore-associated mechanisms of immunity manipulation in plants
show the involvement of siderophore groups like carboxylate (achromobactin,
citrate), hydroxamate (desferrioxamine E, ferrichrome), catecholate (enterobactin,
chrysobactin), phenolate (pyochelin, yersiniabactin), and mixed type (aerobactin
and pyoverdin) (Aznar and Dellagi (2015). The phytopathogenic ascomycetes
Cochliobolus miyabeanus, C. heterostrophus, F. graminearum, and Alternaria brassicicola required the siderophores to resist the activity of hydrogen peroxide in their
respective host’s maize, rice, wheat, and Arabidopsis thaliana (Oide et al. 2006).
The same has been observed in the hemibiotrophic fungus Colletotrichum graminicola (Albarouki et al. 2014) and A. alternata (the causative agent of infection in
citrus) (Chen et al. 2013) ,and the siderophore desferrioxamine renders support in
the fire blight-causing agent Erwinia amylovora by facilitating the infection on
apple seedlings and flowers (Dellagi et al. 1998).
The defense strategies in the case of plants which included phosphorylation
events, reactive oxygen species (ROS) accumulation, cell wall rigidification,
increased deposition of callose, upregulated genes of pathogenesis-related proteins,
and, even more, the induced systemic resistance (ISR) on any disturbance for its
stoichiometric balance of metal homeostasis are reported (Aznar and Dellagi 2015).
The mechanism of immunity induction by siderophores varies among the plant
S. Manoharan et al.