Targeting polyamine metabolism for control of fungal pathogenesis and increasing host resistance during the maize-Aspergillus flavus interaction

Authors: Majumdar, Raj; Cary, Jeffrey; Lebar, Matthew; MINOCHA, RAKESH - Us Forest Service (FS); MINOCHA, SUBHASH - Us Forest Service (FS); Rajasekaran, Kanniah - Rajah; Mack, Brian; LONG, STEPHANIE - Us Forest Service (FS); Carter-Wientjes, Carol; Sickler, Christine

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/26/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Polyamines (PAs) are ubiquitous nitrogenous molecules with diverse functions in living organisms and are known to play an active role during plant-fungus pathogenic interactions. Maize is a major food and feed crop grown worldwide and is highly susceptible to the mycotoxigenic fungus Aspergillus flavus. Upon infection, the fungus produces aflatoxins (carcinogens) and numerous toxic secondary metabolites (SMs). The current study was undertaken to delineate the biological role of PAs in A. flavus development, pathogenesis, SM production, and the contribution of maize PA metabolism in host resistance against the fungus. As spermidine (Spd) is critical for cell survival, we generated an A. flavus 'spds knockout mutant. Inhibiting Spds, negatively affected fungal growth, development, and the 'spds mutant was an auxotroph for Spd. In vitro supply of Spd and Spm significantly increased aflatoxins and production of mature sclerotia along with sclerotial metabolites such as aflavinines, aflatrems, and cyclopiazonic acid. Complementation of the mutant with a wild type (WT) spds gene restored WT phenotype. Infection of maize kernels using the 'spds mutant showed significant reduction in fungal load (>100-fold) and aflatoxin content (>97%) when compared to the control. On the other hand, naturally occurring A. flavus resistant maize lines showed higher accumulation (vs. susceptible line) of Spd and Spm both in mock-inoculated and A. flavus inoculated kernels. High basal expression of maize PA genes (e.g. SAMDC) in the absence of the pathogen and further induction upon A. flavus infection was observed in the resistant lines. The susceptible line accumulated higher amounts of glutamate (Glu), glutamine (Gln), and '-aminobutyric acid (GABA) during early stages of kernel infection compared to the resistant line, suggesting a possible uptake of these amino acids from the maize host by the fungus that contributed to increased pathogenesis. Resistant maize lines accumulated significantly less (>85%) aflatoxins than the susceptible line. The data presented here show the potential of a future hybrid approach by simultaneous targeting A. flavus spds gene (through RNAi mediated host-induced gene silencing) and genetically increasing maize SAMDC gene expression to improve host resistance against A. flavus colonization and aflatoxin production.