DEVELOPING RESISTANCE TO AFLATOXIN THROUGH SEED-BASED TECHNOLOGIES
Location: Food and Feed Safety Research
Title: Identifying cotton (Gossypium hirsutum L.) genes induced in response to Aspergillus flavus infection
Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 9, 2012
Publication Date: August 31, 2012
Citation: Lee, S., Rajasekaran, K., Ramanarao, M.V., Bedre, R., Bhatnagar, D., Baisakh, N. 2012. Identifying cotton (Gossypium hirsutum L.) genes induced in response to Aspergillus flavus infection. Physiological and Molecular Plant Pathology. 80:35-40.
Interpretive Summary: Aspergillus flavus is the primary causal agent of aflatoxin contamination of cottonseed resulting in a significant economic loss and a threat to food security. Improvement of commercial varieties of cotton, either by conventional breeding or by genetic engineering, for resistance to the fungus depends on our understanding of molecular regulation during host-pathogen interaction. As a defense mechanism, several hundreds of genes are turned on when the fungus invades the host cotton plant. How these genes are regulated in different plant tissues of diverse genotypes of cotton under different environmental conditions is not well known. Our current study is one of the first ones to identify a set of differentially-expressed cotton genes induced soon after Aspergillus infection of cotton bolls and seed. This study will provide important clues to the molecular network contributing to the resistance in cottonseed. Results from this study would also help in developing multiple strategies to control preharvest aflatoxin contamination in cottonseed.
Aflatoxin contamination in cottonseed, caused primarily by Aspergillus flavus, is a global concern in terms of food safety and economy. Current strategies to reduce the risk of aflatoxin contamination rely mostly upon biological control with non-aflatoxigenic strains and chemical control measures. Success in enhancing host resistance for eliminating pre-harvest aflatoxin contamination by A. flavus is handicapped by the lack of resistance source available in cotton germplasm. Genetic engineering for aflatoxin-free cotton, as the alternative, warrants for identification of resistance-associated proteins in cotton. As a first step toward this, we isolated 44 genes that were differentially expressed (DEGs) in response to A. flavus infection in pericarp and seed tissues, using annealing control primer system. Four of the DEGs had significant match to cotton-specific genes (legumin A, spot11 catalase, alpha globulin A&B, and cytochrome c oxidase). The DEGs belonged to different functional gene ontology (GO) categories, which suggested that the fungus induced a complex and multi-factorial responses in the cotton plant. Quantitative expression analysis of eight DEGs representing different categories of genes, including transcription factors, kinase, and downstream stress responsive genes, revealed their tissue and time-dependent response to the fungal infection. Identification of fungus induced/regulated genes will provide clues to understanding the underlying resistance response network, which ultimately would help develop multiple strategies to control the aflatoxin contamination in cottonseed. The upregulated genes would have potential use in development of A. flavus resistance in cottonseed through genetic engineering and/or molecular marker-assisted breeding.