Discovery and confirmation of genes/proteins associated with maize aflatoxin resistance

Abstract

Maize (Zea mays L.) is one of the major crops susceptible to Aspergillus flavus infection and subsequent aflatoxin contamination. Many earlier studies indicated the roles of kernel proteins, especially constitutively expressed proteins, in maize resistance to A. flavus infection and aflatoxin production. In this review, we examined the past and current efforts in identifying maize genes and proteins from kernel, rachis, and silk tissues that may play an important role in resistance to A. flavus infection and aflatoxin contamination, as well as the efforts in determining the importance or involvement of them in maize resistance through biochemical, molecular and genetics studies. Through these studies, we gained a better understanding of host resistance mechanism: resistant lines appear to either express some stress-related and antifungal proteins at higher levels in endosperm, embryo, rachis and silk tissues before A. flavus infection or induce the expression of these proteins much faster compared to susceptible maize lines. In addition, we summarised several recent efforts in enhancing maize resistance to aflatoxin contamination using native genes from maize or heterologous and synthetic genes from other sources as well as from A. flavus. These efforts to either suppress A. flavus growth or aflatoxin production, have all shown some promising preliminary success. For example, maize plants transformed with an α-amylase inhibitor protein from Lablab purpurea showed reduced aflatoxin levels by 56% in kernel screening assays. The antifungal potentials of transgenic maize plants expressing synthetic lytic peptides, such as cecropin-based D4E1 or tachyplesin-based AGM peptides with demonstrated antiflavus activity (IC 50 = 2.5 to 10 μM), are yet to be assayed. Further investigation in these areas may provide a more cost-effective alternative to biocontrol in managing aflatoxin contamination in maize and other susceptible crops.

The impact ofBacillus thuringiensis technology on the occurrence of fumonisins and other mycotoxins in maize

“…Kernel screening assays in AILPtransgenic maize plants revealed AF levels 56% lower than controls. AILP expression therefore appears to reduce both fungal growth on the kernels and AF accumulation (Chen et al, 2015).…”

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

“…The α-amylase enzyme is crucial in A. flavus as it is involved in the degradation of the host's carbohydrate reservoir which is an essential energy source for fungus growth and reproduction, as well as AP. Therefore, an α-amylase inhibitor protein (AILP) that inhibits α-amylase activity was expressed in the host; this reduced fungus growth and subsequent AP (Fakhoury and Woloshuk, 2001; see Chen et al, 2015). Recently, a transgenic maize line expressing AGM182 which encodes a tachyplesin1-derived synthetic peptide (an antimicrobial peptide) was developed that exhibited reduced fungal growth and a significant reduction in aflatoxin level (76-98%) compared to the control (Rajasekaran et al, 2018).…”

“…Although some success has been achieved, good management practices are neither very cost effective nor always practical for the resource-poor farmers, or are not effective in reducing aflatoxin content below tolerance thresholds if not used as part of a holistic aflatoxin management strategy. Climate change and frequent extreme weather events, hot and dry conditions, and erratic rainfall have become more pronounced, allowing aflatoxin-producing fungi to thrive, exacerbating the frequency and severity of contamination events (Chen et al, 2015). Heat and drought stresses are the most important abiotic stresses that predispose crops to Aspergillus infection and also affect crop productivity.…”

“…In rainfed areas where farmers are subjected to unavoidable biotic and abiotic stresses that influence aflatoxin accumulation, it is paramount to conduct comprehensive genetics and genomics studies for a better understanding of the genetic behavior, genetic architecture, and molecular mechanisms that govern different types of aflatoxin resistance in groundnut and maize. Several genetic mapping studies conducted in both groundnut and maize have concluded that aflatoxin resistance is a quantitative trait and has complex genetic behavior with high G × E interaction (Chen et al, 2015;Pandey et al, 2019). Hence, by dissecting host-pathogen interactions during fungal infection by aflatoxin producers and aflatoxin contamination, important host-specific, resistance-related genes/proteins/pathways/resistant factors can be characterized in both groundnut and maize.…”

Advances in molecular and genomic research to safeguard food and feed supply from aflatoxin contamination

“…A number of potential maize resistance-associated proteins (RAPs) and the genes encoding them have been identified (Table 2) and some of these have been introduced into other crops for evaluation (Chen et al, , 2007Rajasekaran et al, 2005aRajasekaran et al, , 2008. Proteomic analyses of resistant maize kernels revealed existence of many resistance associated proteins and they have been shown to play an active role in resistance to A. flavus contamination (Chen et al, 2002(Chen et al, , 2015Majumdar et al, 2017b). Unlike maize, there are no well-characterised resistance proteins/genes available in cotton germplasm that demonstrate enhanced resistance to A. flavus infection and aflatoxin contamination.…”