Resistance to Aspergillus flavus in Corn Kernels Is Associated with a 14-kDa Protein

Abstract

Corn genotypes resistant or susceptible to Aspergillus flavus were extracted for protein analysis using a pH 2.8 buffer. The profile of protein extracts revealed that a 14-kDa protein is present in relatively high concentration in kernels of seven resistant corn genotypes, but is absent or present only in low concentration in kernels of six susceptible ones. The N-terminal sequence of this 14-kDa protein showed 100% homology to a corn trypsin inhibitor. The 14-kDa protein purified from resistant varieties also demonstrated in vitro inhibition of both trypsin activity and the growth of A. flavus. This is the first demonstration of antifungal activity of a corn 14-kDa trypsin inhibitor protein. The expression of this protein among tested genotypes may be related to their difference in resistance to A. flavus infection and subsequent aflatoxin contamination.

Aflatoxins: Mechanisms of Inhibition by Antagonistic Plants and Microorganisms

“…A RAP from maize kernel, the 14 kDa trypsin inhibitor, in resistance to fungal invasion and AF contamination has been confirmed (Brown et al, 2010 and references therein). This trypsin inhibitor indirectly suppresses AF production by inhibiting -amylase of A. flavus, a fungal pathogenesis factor (Chen et al, 1998;Fakhoury & Woloshuk, 1999). Extracellular hydrolases of A. flavus including -amylase are responsible for degrading starch to glucose and maltose used for fungal growth.…”

Identifying Aflatoxin Resistance-related Proteins/Genes through Proteomics and RNAi Gene Silencing1

“…A more rapid and stronger induction of the pathogenesis-related (pr1 and pr5) genes in maize leaves has also been observed in a resistant reaction when compared to a susceptible reaction upon pathogen infection (Morris et al, 1998). In another investigation, a 14 kDa trypsin inhibitor (TI) protein was found constitutively produced at high levels in resistant lines but at low levels or was missing in susceptible ones (Chen et al, 1998). This protein demonstrated antifungal activity against A. flavus and several other pathogenic fungi , possibly through inhibition of fungal a-amylase activity and production.…”

“…McMillian et al (1993) released the maize population GT-MAS:gk as a source of resistance to aflatoxin accumulation. To use the resistance traits from GT-MAS:gk, such as physical pericarp wax (Guo et al, 1995(Guo et al, , 1996Russin et al, 1997) and antifungal proteins Chen et al, 1998), efforts of self-pollination and selection have been made since 1996 for reduced aflatoxin contamination. By evaluating S1 families, Guo et al (2001) demonstrated that considerable variation among the individual plants within the population GT-MAS:gk was detectable using random amplified polymorphic DNA (RAPD) markers and a laboratory aflatoxin bioassay.…”

Development of Maize Host Resistance to Aflatoxigenic Fungi

“…In another investigation, an examination of kernel protein profiles of 13 maize genotypes revealed that a 14 kDa trypsin inhibitor protein (TI) is present at relatively high concentrations in seven resistant maize lines, but at low concentrations or is absent in six susceptible lines [43]. The mode of action of TI against fungal growth may be partially due to its inhibition of fungal -amylase, limiting A. flavus access to simple sugars [44] required not only for fungal growth, but also for toxin production [45].…”