Submitted to: African Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2010
Publication Date: November 1, 2010
Citation: Fountain, J.C., Chen, Z.Y., Scully, B.T., Kemerait, R.C., Lee, R.D., Guo, B. 2010. Pathogenesis-related gene expressions in different maize genotypes under drought stressed conditions. African Journal of Plant Science. 4(11):433-440. Interpretive Summary: The infection and proliferation of Aspergillus flavus in corn results in the production of several carcinogenic mycotoxins collectively referred to as aflatoxins. The production of aflatoxins is exacerbated by exposure of A. flavus to elevated temperatures and low relative humidity. Drought stress has the ability to retard maize resistance to the growth of A. flavus and subsequent pre- and post-harvest aflatoxin production and accumulation. In this study, the expression of three genes in different maize genotypes was compared in order to determine their possible roles in host resistance in response to drought stress. Genotypes possessing aflatoxin resistance were hypothesized to exhibit a significant up-regulation in defense-related gene expression while possibly susceptible genotypes were expected to exhibit significant down-regulation of these genes assuming that such observed patterns of variation in transcript levels correlate to those of actual translated proteins in the genotypes examined in this study. This was evaluated utilizing both semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) and the quantitative real-time RT-PCR (qPCR). The data suggested that drought stress during kernel development in the field affected the gene expression differently in different genotypes. Such expression patterns combined with the results of previous studies show that these stress-related resistance-associated proteins (RAP’s) may play a role in corn resistance to A. flavus infection and subsequent aflatoxin contamination.
Technical Abstract: Aflatoxins are carcinogenic mycotoxins produced by the fungus Aspergillus flavus during infection of grain crops including maize (Zea mays). Contamination of maize grain with aflatoxin is exacerbated by late season drought stress. Previous studies have identified numerous resistance-associated proteins (RAP’s) that may be responsible for resistance to A. flavus proliferation and aflatoxin production. The present study examined the expression of three genes encoding RAP’s ZmPR-10 (PR-10), glyoxalase I (GLX-I), and a 14-kDa trypsin inhibitor (TI-14) in different maize genotypes; and determined whether there is any potential utility as selection markers for resistance to aflatoxin contamination. The expression of these genes was evaluated in 2007 and 2008 in drought stress versus well-watered conditions using RT-PCR and real-time qPCR. The semi-quantitative RT-PCR with 20 cycles was not as sensitive as real-time qPCR. The data suggested that drought stress during kernel development in the field affected the gene expression differently in different genotypes. In general, the expression of pr-10 was lower overall as compared to glx-I and ti-14; some genotypes, such as CLQ-G2507, generally had higher constitutive levels of gene expression while other genotypes, such as B73, had relatively low gene expression. Exceptions, such as Lo964, possessed lower levels of expression of one gene but higher expression of others. This study was partly consistent with expectations in that elevated levels of RAP-coding gene expression generally correlated to known resistive qualities of the examined genotypes to A. flavus infection and subsequent aflatoxin contamination. However, this study was unable to conclude whether these genes could be used as selection markers.