Changes in bacterial endophyte community following aspergillus flavus infection in resistant and susceptible maize kernels

Authors: Majumdar, Raj; Kandel, Shyam; Cary, Jeffrey; Rajasekaran, Kanniah - Rajah

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2021
Publication Date: 4/3/2021
Citation: Majumdar, R., Kandel, S.L., Cary, J.W., Rajasekaran, K. 2021. Changes in bacterial endophyte community following aspergillus flavus infection in resistant and susceptible maize kernels. International Journal of Molecular Sciences. 22(7). Article 3747. https://doi.org/10.3390/ijms22073747.
DOI: https://doi.org/10.3390/ijms22073747

Interpretive Summary: Aspergillus flavus (A. flavus) infects maize and other economically important crops such as peanut, tree nuts etc. Upon infection, the fungus produces aflatoxins which are potent carcinogens. Aflatoxin contamination of food and feed crops negatively impact crop value and pose serious threat to mankind and livestock. Amongst different pre-harvest aflatoxin mitigation strategies employed, biological control of A. flavus has been the most effective to date on a global scale though, often unable to reduce aflatoxin levels below the threshold recommended by regulatory agencies in food and feed. Therefore, additional pre-harvest aflatoxin control strategies are being developed to complement current biological control strategy. Earlier studies have demonstrated the role of host plant microbiome in resistance against pathogenic fungi, bacteria, viruses etc. besides their beneficial roles against abiotic stress. As A. flavus is a kernel specific pathogen in maize, identification of kernel specific endophytes with potential anti A. flavus activities will be of great utility towards the development of novel mitigation strategies. Using A. flavus resistant maize breeding lines along with a susceptible line, we investigated the role of bacterial endophytes in resistance against A. flavus and aflatoxin production during kernel infection. We have identified bacterial endophytes with potential anti-A. flavus and anti-aflatoxigenic properties in the resistant lines that will assist in the development of novel biocontrol agents in the future.

Technical Abstract: Aspergillus flavus (A. flavus) mediated aflatoxin contamination in maize is a major global economic and health concern. As A. flavus is an opportunistic seed pathogen, identification of factors contributing to kernel resistance will be of great importance in the development of novel mitigation strategies. Using V3–V4 bacterial rRNA sequencing and seeds of A. flavus resistant maize breeding lines TZAR102 and MI82 and a susceptible line, SC212, we investigated kernel specific changes of bacterial endophytes during infection. A total of 81 bacterial genera belonging to 10 phyla were detected. Bacteria belonging to the phylum Tenericutes comprised 86-99% of detected phyla followed by Proteobacteria (14%), and others (<5%) that changed with treatments and/or genotypes. Higher basal levels (without infection) of Streptomyces, and Microbacterium and increases in the abundance of Stenotrophomonas and Sphingomonas in the resistant lines following infection may suggest their role in resistance. Functional profiling of bacteria using 16S rRNA sequencing data revealed the presence of bacteria associated with the production of putative antifungal type II polyketides, sesquiterpenoids in the resistant vs. susceptible lines. Future characterization of endophytes predicted to possess antifungal/ anti-aflatoxigenic properties will aid in their development as effective biocontrol agents or microbiome markers for maize aflatoxin resistance.