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4.5.2 Siderophores Regulation by Cell Receptors
Animals can neutralize iron scavengers from pathogens through siderocalins, by
binding with certain iron–siderophores, that limiting microorganism iron nutrition.
However, microorganisms can secrete more than one siderophore, but some siderocalins, such as Lcn1, can recognize and bind siderophores with diverse structures. In
plants, no such recognition mechanism has been reported so far. Although a phylogenetic study of the plant lipocalin family identifies proteins that show some similarity
with animal lipocalins, siderocalins are not reported in this study (Frenette Charron
2005). Aznar and Dellagi (2015) performed a BLAST search to identify proteins
similar to siderocalins, using the protein coding for Neutrophil gelatinase-associated
lipocalin (NGAL) and Lcn1 and found no plant orthologues, and they suggested if
siderophores recognition exists in plants, then it is probably based on another type of
protein. Information is still lacking, whether siderophores can be identified by specific receptors in plants, similar to MAMPs and how they are identified by PRRs
(pattern recognition receptors). Albarouki et al. (2014) reported in maize that the
accumulation of ROS and upregulation of the PR gene occur in response to both
siderophores coprogen and Fe-coprogen, indicating that a receptor could detect siderophores in maize. The transcriptomic analysis of siderophores DFO is very similar
to the transcriptome of plants infected by plant pathogens (Aznar and Dellagi 2015).
This similarity may determine that the ratio of the signaling cascade activated
after detection of siderophores is similar to that of a MAMP or an attack of pathogens.
Dellagi et al. (2009) suggested that the SA upregulation via DFO depends on proteins
NPR1, EDS5, and SID2, which are considered to be main regulators of the plant’s
response to pathogens (Quartin et al. 2001). It is believed that Response Regulator
Protein (RRP) is dedicated to the recognition of microbial siderophores. Alternatively,
siderophores can determine the activity of one or more proteins, in the case of pathogenic effectors, which is associated with the modification of a metalloprotein. The
immune response will be activated if this target protein is protected by resistance
proteins, such as those in nucleotide-binding leucine-rich repeat NB-LRR family. In
Maize, for example iron scavenging effect does ssem to involved in the process of
activation of defense by the coprogen (Albarouki et al. 2014).
4.6 Siderophore-Mediated Plant Immunity Activation
Recently, molecular approaches suggested that various plant species are able to activate immune programs in response to siderophore treatment. For example, in maize,
the effect of the coprogen seems more reminiscent of “priming” (Albarouki et al.
2014), while in Arabidopsis the coprogenic effect resembles direct stress (Aznar
and Dellagi 2015). In the studies described below, oxidative stress has been reported
in several cases. ROS production is associated with the combination of pyochelin
and pyocyanin in tomato cells, with the siderophores Psb374 in tobacco cell cul4 Siderophores: Mediated Iron Acquisition and Virulence of Brown Rot Disease…
4.5.2 Siderophores Regulation by Cell Receptors
Animals can neutralize iron scavengers from pathogens through siderocalins, by
binding with certain iron–siderophores, that limiting microorganism iron nutrition.
However, microorganisms can secrete more than one siderophore, but some siderocalins, such as Lcn1, can recognize and bind siderophores with diverse structures. In
plants, no such recognition mechanism has been reported so far. Although a phylogenetic study of the plant lipocalin family identifies proteins that show some similarity
with animal lipocalins, siderocalins are not reported in this study (Frenette Charron
2005). Aznar and Dellagi (2015) performed a BLAST search to identify proteins
similar to siderocalins, using the protein coding for Neutrophil gelatinase-associated
lipocalin (NGAL) and Lcn1 and found no plant orthologues, and they suggested if
siderophores recognition exists in plants, then it is probably based on another type of
protein. Information is still lacking, whether siderophores can be identified by specific receptors in plants, similar to MAMPs and how they are identified by PRRs
(pattern recognition receptors). Albarouki et al. (2014) reported in maize that the
accumulation of ROS and upregulation of the PR gene occur in response to both
siderophores coprogen and Fe-coprogen, indicating that a receptor could detect siderophores in maize. The transcriptomic analysis of siderophores DFO is very similar
to the transcriptome of plants infected by plant pathogens (Aznar and Dellagi 2015).
This similarity may determine that the ratio of the signaling cascade activated
after detection of siderophores is similar to that of a MAMP or an attack of pathogens.
Dellagi et al. (2009) suggested that the SA upregulation via DFO depends on proteins
NPR1, EDS5, and SID2, which are considered to be main regulators of the plant’s
response to pathogens (Quartin et al. 2001). It is believed that Response Regulator
Protein (RRP) is dedicated to the recognition of microbial siderophores. Alternatively,
siderophores can determine the activity of one or more proteins, in the case of pathogenic effectors, which is associated with the modification of a metalloprotein. The
immune response will be activated if this target protein is protected by resistance
proteins, such as those in nucleotide-binding leucine-rich repeat NB-LRR family. In
Maize, for example iron scavenging effect does ssem to involved in the process of
activation of defense by the coprogen (Albarouki et al. 2014).
4.6 Siderophore-Mediated Plant Immunity Activation
Recently, molecular approaches suggested that various plant species are able to activate immune programs in response to siderophore treatment. For example, in maize,
the effect of the coprogen seems more reminiscent of “priming” (Albarouki et al.
2014), while in Arabidopsis the coprogenic effect resembles direct stress (Aznar
and Dellagi 2015). In the studies described below, oxidative stress has been reported
in several cases. ROS production is associated with the combination of pyochelin
and pyocyanin in tomato cells, with the siderophores Psb374 in tobacco cell cul4 Siderophores: Mediated Iron Acquisition and Virulence of Brown Rot Disease…