Genome-Wide Transcriptome Analysis of Cotton (Gossypium hirsutum L.) Identifies Candidate Gene Signatures in Response to Aflatoxin Producing Fungus Aspergillus flavus

Abstract

Aflatoxins are toxic and potent carcinogenic metabolites produced from the fungi Aspergillus flavus and A. parasiticus. Aflatoxins can contaminate cottonseed under conducive preharvest and postharvest conditions. United States federal regulations restrict the use of aflatoxin contaminated cottonseed at >20 ppb for animal feed. Several strategies have been proposed for controlling aflatoxin contamination, and much success has been achieved by the application of an atoxigenic strain of A. flavus in cotton, peanut and maize fields. Development of cultivars resistant to aflatoxin through overexpression of resistance associated genes and/or knocking down aflatoxin biosynthesis of A. flavus will be an effective strategy for controlling aflatoxin contamination in cotton. In this study, genome-wide transcriptome profiling was performed to identify differentially expressed genes in response to infection with both toxigenic and atoxigenic strains of A. flavus on cotton (Gossypium hirsutum L.) pericarp and seed. The genes involved in antifungal response, oxidative burst, transcription factors, defense signaling pathways and stress response were highly differentially expressed in pericarp and seed tissues in response to A. flavus infection. The cell-wall modifying genes and genes involved in the production of antimicrobial substances were more active in pericarp as compared to seed. The genes involved in auxin and cytokinin signaling were also induced. Most of the genes involved in defense response in cotton were highly induced in pericarp than in seed. The global gene expression analysis in response to fungal invasion in cotton will serve as a source for identifying biomarkers for breeding, potential candidate genes for transgenic manipulation, and will help in understanding complex plant-fungal interaction for future downstream research.

Infection with toxigenic and atoxigenic strains of Aspergillus flavus induces different transcriptional signatures in maize kernels

“…Different isoforms of chitinases were induced by infection with both atoxigenic and toxigenic A. flavus in cotton pericarp and seed (Bedre et al 2015). Furthermore, a chitinase A positioned in bin 2.04 was associated with a large aflatoxin reducing QTL, as reported by Hawkins et al (2015).…”

“…This inhibition was correlated with the activity levels of β-1,3-glucanase in the callus and in the culture medium. Bedre and co-workers (2015) reported that two β-1,3-glucanases (BG1 and BG3) were highly induced by an atoxigenic strain of A. flavus on cotton seed, whereas another BG3 transcript was upregulated specifically by the toxigenic strain (Bedre et al 2015). The hydrolytic enzymes β-1,3-glucanase and chitinase, such as PRm3, possess antifungal activity by degrading the fungal cell wall containing chitins ).…”

“…On the other hand no expression changes were observed for WRKY110 gene (designated as WRKY30), suggesting that it may respond primarily to environmental stress and not to pathogen infections (Wei et al 2012). Recent transcriptional profiling studies have shown that 28 WRKY-related transcripts were differentially expressed under toxigenic and atoxigenic strains of A. flavus in cotton seed and pericarp tissues (Bedre et al 2015). Most of the WRKY TFs were upregulated under the atoxigenic strain infection in pericarp and the toxigenic strain infection in seed, with the exception of WRKY75 and WRKY40 genes that were specifically upregulated under the atoxigenic strain in both tissues.…”

“…role in the mechanism of resistance against this pathogen (Bedre et al 2015). Prior research illustrated the role of lipids, particularly oxylipins, in the specific interaction between maize and A. flavus and in regulating aflatoxin biosynthesis ).…”

RNA Sequencing of Contaminated Seeds Reveals the State of the Seed Permissive for Pre-Harvest Aflatoxin Contamination and Points to a Potential Susceptibility Factor

“…In cotton, inoculated bolls were harvested in a time series after inoculation and subjected to RNA sequencing [25]. Differential expression analysis found an up-regulation of defense-related and antifungal genes in pericarp and seeds in response to Aspergillus [25]. Dolezal et al, 2014 [26] inoculated maize kernels and profiled expression with a maize microarray at four days after infection.…”