Dual targeting of polyamine (PA) metabolism by inhibiting fungal PA biosynthesis and transport as a strategy to control Aspergillus flavus infection and aflatoxin contamination in corn

Targeting polyamine (PA) metabolism in phytopathogenic fungi has been reported to be an effective strategy to restrict fungal growth and virulence. PAs are small aliphatic polycations involved in plethora of cellular processes including interactions with DNA (replication, transcription, and translation), transporter function, and scavenging of oxidative stress molecules to name a few.  In fungi, the diamine putrescine (Put) is produced from ornithine (Orn) via ornithine decarboxylase (ODC; rate-limiting step). Higher PAs (more than two amine groups), spermidine (Spd) and spermine (Spm) are produced from Put and Spd respectively. Aspergillus flavus is a contaminant of corn and several other oil-seed crops where it produces aflatoxin upon infection resulting in substantial reduction in value of the crop. While Put is primarily associated with hyphal growth, Spd is implicated in the cellular events associated with sporulation in Aspergillus sp. Impairing PA metabolism is shown to restrict A. flavus growth/virulence/toxin production under in vitro condition. On the other hand, earlier studies have shown that a PA mutated fungi when re-introduced back in to plants, resulted in restoration of virulence possibly due to the uptake of PAs from host and partially compensating PA depletion in the pathogen. We have used gene knockout or knock down using RNA interference to silence the ODC (Put biosynthesis) and plasma membrane-bound PA transporter (putative) genes in A. flavus.  Data will be presented on the role of ODC and PA transporters in A. flavus growth and development, toxin production and virulence under in vitro and in vivo (plant-pathogen interaction) conditions.