Insight into Genes Regulating Postharvest Aflatoxin Contamination of Tetraploid Peanut from Transcriptional Profiling

Abstract

Postharvest aflatoxin contamination is a challenging issue that affects peanut quality. Aflatoxin is produced by fungi belonging to the Aspergilli group, and is known as an acutely toxic, carcinogenic, and immune-suppressing class of mycotoxins. Evidence for several host genetic factors that may impact aflatoxin contamination has been reported, , genes for lipoxygenase (PnLOX1 and PnLOX2/PnLOX3 that showed either positive or negative regulation with infection), reactive oxygen species, and WRKY (highly associated with or differentially expressed upon infection of maize with ); however, their roles remain unclear. Therefore, we conducted an RNA-sequencing experiment to differentiate gene response to the infection by between resistant (ICG 1471) and susceptible (Florida-07) cultivated peanut genotypes. The gene expression profiling analysis was designed to reveal differentially expressed genes in response to the infection (infected mock-treated seeds). In addition, the differential expression of the fungal genes was profiled. The study revealed the complexity of the interaction between the fungus and peanut seeds as the expression of a large number of genes was altered, including some in the process of plant defense to aflatoxin accumulation. Analysis of the experimental data with "keggseq," a novel designed tool for Kyoto Encyclopedia of Genes and Genomes enrichment analysis, showed the importance of α-linolenic acid metabolism, protein processing in the endoplasmic reticulum, spliceosome, and carbon fixation and metabolism pathways in conditioning resistance to aflatoxin accumulation. In addition, coexpression network analysis was carried out to reveal the correlation of gene expression among peanut and fungal genes. The results showed the importance of WRKY, toll/Interleukin1 receptor-nucleotide binding site leucine-rich repeat (TIR-NBS-LRR), ethylene, and heat shock proteins in the resistance mechanism.

Pod and seed trait QTL identification to assist breeding for peanut market preferences

“…This supports our finding of QTL co-localized on A07 for KP 456 with previously mapped percentage of pod maturity (Fonceka et al 2012). This 457 demonstrates that maturity can be indirectly measured and that our population is likely 458 segregating for maturity, since both parents of the population have different maturity 459 ranges, Tifrunner being a late maturity peanut with ~150 days after planting (Holbrook 460 and Culbreath 2007) and NC 3033 with an earlier maturity of ~135 days after planting 461 (Beute et al 1976;Korani et al 2018). At the time of harvest, when seed and pod filling 462 is complete and the seeds have accumulated storage products, the seed density is higher 463 than in immature seeds (Williams et al 1987;Sanders 1989;Rucker et al 1994b).…”

Functional Biology and Molecular Mechanisms of Host-Pathogen Interactions for Aflatoxin Contamination in Groundnut (Arachis hypogaea L.) and Maize (Zea mays L.)

“…To understand the post-harvest resistance mechanism, Wang et al (2016) performed global transcriptome profiling in the grains of resistant (Zhonghua 6) and susceptible (Zhonghua 12) genotypes of groundnut and identified 30,143 DEGs, of which 842 were defense-related genes, including mitogen-activated protein kinase, PR proteins, leucine-rich repeat receptor-like kinases transcription factors, nucleotide-binding site-leucinerich repeat proteins, polygalacturonase inhibitor proteins, and ADP-ribosylation factors in response to AP by A. flavus. A recent study by Korani et al (2018) provides new insights into postharvest resistance mechanism in response to A. flavus infection by comparing the seed transcriptome of resistant (ICG 1471) and susceptible (Florida-07) groundnut cultivars. The study identified 4,272 DEGs and showed the importance of WRKY TFs, heat shock proteins and TIR-NBS-LRR in providing resistance.…”

“…Aspergillus infection also involves a dynamic network of transcription factors that coordinate the expression of the target biosynthetic genes of the pathogen and the suppression of the host's immune responses. This may involve the suppression of key gene WRKY, a transcription factor that modulates the expression of several genes involved in detoxification of ROS as well as aflatoxin (Korani et al, 2018), including NBS-LRR; its suppression is linked to aggravated accumulation of aflatoxin in plants such as groundnut (Nayak et al, 2017). Further, these TFs are also associated with PR proteins, which play a major role in resistance after infection (Pierpoint et al, 1981;Van Loon, 1985;Szerszen, 1990;Van Loon and Van Strien, 1999).…”

“…Further, these TFs are also associated with PR proteins, which play a major role in resistance after infection (Pierpoint et al, 1981;Van Loon, 1985;Szerszen, 1990;Van Loon and Van Strien, 1999). In groundnut, WRKY and other key TFs such as ERF and NAC function in a coordinated fashion (Nayak et al, 2017;Korani et al, 2018); their modulation has a substantial impact on antioxidant biosynthetic, PR proteins, chitinase, and beta-1,3-glucanase genes. Modulation of these TFs in the host severely affects the transcription of ROS detoxifying genes such as catalases, superoxide dismutase, glutathione-S-transferase, and antioxidant biosynthesis genes like resveratrol synthase, PAL, chalcone synthase, chitinase, and beta-1,3-glucanase (Nayak et al, 2017;Korani et al, 2018).…”

“…In groundnut, WRKY and other key TFs such as ERF and NAC function in a coordinated fashion (Nayak et al, 2017;Korani et al, 2018); their modulation has a substantial impact on antioxidant biosynthetic, PR proteins, chitinase, and beta-1,3-glucanase genes. Modulation of these TFs in the host severely affects the transcription of ROS detoxifying genes such as catalases, superoxide dismutase, glutathione-S-transferase, and antioxidant biosynthesis genes like resveratrol synthase, PAL, chalcone synthase, chitinase, and beta-1,3-glucanase (Nayak et al, 2017;Korani et al, 2018). These genes protect host plants from oxidative damage, increase the levels of secondary metabolites involved in lignin biosynthesis, and restrict fungal invasion as well as its growth.…”