|YANG, LIMING - University Of Georgia
|FOUNTAIN, JAKE - University Of Georgia
|JI, PINGSHENG - University Of Georgia
|CHEN, SIXUE - University Of Florida
|LEE, ROBERT - University Of Georgia
|KEMERAIT, ROBERT - University Of Georgia
Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2018
Publication Date: 2/12/2018
Citation: Yang, L., Fountain, J.C., Ji, P., Ni, X., Chen, S., Lee, R.D., Kemerait, R.C., Guo, B. 2018. Deciphering drought-induced metabolic responses and regulation in developing maize kernels. Plant Biotechnology Journal. 16:1616-1628. https://doi.org/10.1111/pbi.12899.
Interpretive Summary: Corn kernels are particularly susceptible to the negative effects of drought stress during grain-filling, a period also of interest from a disease resistance perspective. Kernel tissues become susceptible to A. flavus colonization and pre-harvest aflatoxin contamination beginning at the initiation of grain filling at the R2 – R3 growth stage, 7 to 14 days after pollination. This period is also used in field-based resistance screening for germplasm resistance to aflatoxin contamination for artificial A. flavus inoculation. As reactive oxygen species (ROS), which accumulate in maize tissues under drought stress, have been shown to stimulate the production of aflatoxin by A. flavus in vitro and is hypothesized to do so in vivo during colonization of stressed host tissues. The objective was to study corn kernel metabolites including starch, simple sugars, and polyunsaturated fatty acids in order to identify the possible biomarkers associated with the susceptibility to A. flavus infection and subsequently aflatoxin contamination. We examined the metabolite accumulation patterns in developing kernels using an untargeted global metabolomics analysis to compare the metabolomic responses of two corn inbred lines with contrasting drought tolerance and levels of aflatoxin contamination to drought stress. By characterizing the metabolite profiles, a better understanding of the influences of drought stress on kernel development can be obtained. In addition, compounds potentially contributing to pre-harvest aflatoxin contamination resistance can also be identified. Together, these results can be used in molecular breeding and biotechnological applications to improve maize disease resistance, quality, and yield under drought stress.
Technical Abstract: Aspergillus flavus is a facultative pathogen of crops such as maize and peanut which produces carcinogenic aflatoxins during infection, particularly in drought stressed host plants. Reactive oxygen species (ROS) have been shown to both accumulate in host plant tissues during drought and to stimulate the production of aflatoxin by A. flavus both in vitro and in vivo. In order to understand the role of aflatoxin production in oxidative stress responses in A. flavus, we previously examined the transcriptomes of field isolates of A. flavus. To validate this and to examine these responses at the protein level, here we performed iTRAQ (Isobaric Tags for Relative and Absolute Quantification) proteomics for three isolates: AF13 (+++), NRRL3357 (+), and K54A (-) in aflatoxin conducive medium amended with varying levels of H2O2. Proteomic analysis showed that 1173 proteins were detected in at least two replicates. Of these greater numbers of differentially expressed proteins were detected in isolates with less oxidative stress tolerance. Correlative analysis between this proteome data and the transcriptome data for the same conditions showed a weak correlation (r = 0.1114) indicative of possible post-transcriptional regulation. Biochemical pathways including carbon metabolism, glutathione metabolism, oxidative stress regulation, and secondary metabolite biosynthesis comprised the most commonly differentially expressed mechanisms observed. Highly toxigenic isolates exhibited greater expression of lytic enzymes and sclerotial developmental proteins while less toxigenic isolates mainly displayed regulation of antioxidant and primary metabolic pathways. The environmental stress tolerance mechanisms employed by these isolates provide direction for the enhancement of host resistance through the manipulation of host antioxidant capacity and lytic enzyme inhibitor activity using biomarker selection in breeding programs and through novel biotechnologies such as genome editing in crops.