Relationships between C6−C12Alkanal and Alkenal Volatile Contents and Resistance of Maize Genotypes toAspergillus flavusand Aflatoxin Production

Maize genotypes resistant or susceptible to aflatoxin production or contamination were compared for differences in both constitutive and inducible proteins. Five additional constitutive proteins were found to be associated with resistance in over 8 of the 10 genotypes examined. Among these, the 58- and 46-kDa proteins were identified as globulin-1 and globulin-2, respectively. Differences in the ability to induce specific antifungal proteins, such as the higher synthesis of the 22-kDa zeamatin in resistant genotypes, were also observed between resistant and susceptible kernels incubated under germinating conditions (31°C, 100% humidity). Both constitutive and inducible proteins appear to be necessary for kernel resistance. Embryo-killed kernels (unable to synthesize new proteins) supported the highest level of aflatoxins, whereas imbibed kernels (to hasten protein induction) supported the lowest among all treatments. This suggests that the synthesis of new proteins by the embryo plays an important role in conferring resistance. However, significantly lower levels of aflatoxin production in embryo-killed resistant kernels than in susceptible ones suggest that, in reality, high levels of constitutive antifungal proteins are indispensable to kernel resistance.

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Identification of a Maize Kernel Pathogenesis-Related Protein and Evidence for Its Involvement in Resistance to Aspergillus flavus Infection and Aflatoxin Production

Phytopathology ◽

10.1094/phyto-96-0087 ◽

2006 ◽

Vol 96 (1) ◽

pp. 87-95 ◽

Cited By ~ 72

Author(s):

Z.-Y. Chen ◽

R. L. Brown ◽

K. Rajasekaran ◽

K. E. Damann ◽

T. E. Cleveland

Keyword(s):

Aspergillus Flavus ◽

Fungal Growth ◽

Aflatoxin Production ◽

Related Protein ◽

Susceptible Genotype ◽

Leaf Extracts ◽

Maize Genotypes ◽

Resistant Lines ◽

Pathogenesis Related Protein ◽

Pathogenesis Related

Aflatoxins are carcinogens produced by Aspergillus flavus and A. parasiticus during infection of susceptible crops such as maize. Several aflatoxin-resistant maize genotypes have been identified and kernel proteins have been suggested to play an important role in resistance. In the present study, one protein (#717), which was expressed fivefold higher in three resistant lines compared with three susceptible ones, was identified using proteomics. This protein was sequenced and identified as a pathogenesis-related protein (PR-10) based on its sequence homology. To assess the involvement of this PR-10 protein (ZmPR-10) in host resistance of maize against fungal infection and aflatoxin production, the corresponding cDNA (pr-10) was cloned. It encodes a protein of 160 amino acids with a predicted molecular mass of 16.9 kDa and an iso-electric point of 5.38. The expression of pr-10 during kernel development increased fivefold between 7 and 22 days after pollination, and was induced upon A. flavus infection in the resistant but not in the susceptible genotype. The ZmPR-10 overexpressed in Escherichia coli exhibited a ribonucleolytic and antifungal activities. Leaf extracts of transgenic tobacco plants expressing maize pr-10 also demonstrated RNase activity and inhibited the growth of A. flavus. This evidence suggests that ZmPR-10 plays a role in kernel resistance by inhibiting fungal growth of A. flavus.

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Identification of a Maize Kernel Stress-Related Protein and Its Effect on Aflatoxin Accumulation

Phytopathology ◽

10.1094/phyto.2004.94.9.938 ◽

2004 ◽

Vol 94 (9) ◽

pp. 938-945 ◽

Cited By ~ 80

Author(s):

Z.-Y. Chen ◽

R. L. Brown ◽

K. E. Damann ◽

T. E. Cleveland

Keyword(s):

Regulatory Gene ◽

Aflatoxin Production ◽

Glyoxalase I ◽

Constitutive Activity ◽

Aflatoxin Biosynthesis ◽

Maize Kernel ◽

Kernel Infection ◽

Maize Genotypes ◽

Aflatoxin Accumulation ◽

Resistant Genotypes

Aflatoxins are carcinogens produced mainly by Aspergillus flavus during infection of susceptible crops such as maize. Through proteomic comparisons of maize kernel embryo proteins of resistant and susceptible genotypes, several protein spots previously were found to be unique or upregulated in resistant embryos. In the present study, one of these protein spots was sequenced and identified as glyoxalase I (GLX-I; EC 4.4.1.5). The full-length cDNA of the glyoxalase I gene (glx-I) was cloned. GLX-I constitutive activity was found to be significantly higher in the resistant maize lines compared with susceptible ones. After kernel infection by A. flavus, GLX-I activity remained lower in susceptible genotypes than in resistant genotypes. However, fungal infection significantly increased methylglyoxal (MG) levels in two of three susceptible genotypes. Further, MG was found to induce aflatoxin production in A. flavus culture at a concentration as low as 5.0 μM. The mode of action of MG may be to stimulate the expression of aflR, an aflatoxin biosynthesis regulatory gene, which was found to be significantly upregulated in the presence of 5 to 20 μM MG. These data suggest that GLX-I may play an important role in controlling MG levels inside kernels, thereby contributing to the lower levels of aflatoxins found in resistant maize genotypes.

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Wax and Cutin Layers in Maize Kernels Associated with Resistance to Aflatoxin Production by Aspergillus flavus

Journal of Food Protection ◽

10.4315/0362-028x-58.3.296 ◽

1995 ◽

Vol 58 (3) ◽

pp. 296-300 ◽

Cited By ~ 59

Author(s):

BAO Z. GUO ◽

JOHN S. RUSSIN ◽

THOMAS E. CLEVELAND ◽

ROBERT L. BROWN ◽

NEIL W. WIDSTROM

Keyword(s):

Aspergillus Flavus ◽

Potassium Hydroxide ◽

Aflatoxin Production ◽

Maize Kernel ◽

Maize Hybrids ◽

Maize Population ◽

Maize Genotypes ◽

Aflatoxin Accumulation ◽

Maize Kernels ◽

Susceptible Group

Thirteen maize hybrids and one maize population, MAS:gk, were screened for susceptibility to aflatoxin production by Aspergillus flavus. Marked differences in aflatoxin B1 production were detected among the maize genotypes tested. Most commercial hybrids consistently supported high levels of aflatoxin accumulation. Aflatoxin levels did not differ between intact and wounded kernels of these genotypes. However, different results were obtained from 4 of the 13 hybrids and the maize population MAS:gk. Levels of aflatoxin accumulation in intact kernels of these genotypes were lower than in the previous susceptible group of genotypes. In addition, aflatoxin levels were higher in wounded than in intact kernels. MAS:gk not only supported the lowest levels of aflatoxin production in intact kernels, but aflatoxin levels in endosperm-wounded kernels also were significantly lower in MAS:gk than in wounded kernels of all tested hybrids. Treatment with KOH to remove cutin from intact kernels prior to inoculation with A. flavus effected substantial increases in aflatoxin accumulation in MAS:gk, but only marginal increases in the susceptible hybrid Pioneer 3154. Removing wax from the surface of MAS:gk kernels greatly increased the susceptibility of this genotype to aflatoxin accumulation. When wax removal was combined with treatment with potassium hydroxide (KOH) or purified cutinase, aflatoxin levels in kernels were equal to those in wounded control kernels in both genotypes. These results indicated that wax and cutin layers of maize kernel pericarps may play a role in resistance to aflatoxin accumulation in MAS:gk and some other genotypes. However, results suggest further that resistance in MAS:gk also may be due to other preformed compounds as well.

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