| The main focus of this study was to gain deeper understanding of maize resistance to Aspergillus flavus and aflatoxins, carcinogenic compounds that it produces. The study was primarily aimed at investigating the rachis, maternal ear tissue that delivers nutrients to the kernels and whose possible role in the resistance was suggested. Towards this goal the main objectives were: (1) to provide global proteome profiling of rachis tissue from resistant inbred Mp313E, (2) to identify rachis proteins that may be associated with the resistance and (3) to identify A. flavus-responsive rachis proteins.; By using combined gel-based and gel-free proteomic tools and mass spectrometry, 1,690 proteins were identified in developing rachis from resistant genotype Mp313E, representing the most comprehensive protein profile of maize tissue to date. Functional classification according to Gene Ontology revealed that young rachis contains proteins of diverse cellular activities, the majority of which were shown to be involved in various aspects of metabolism and transport. Comparative proteomic approaches of rachis proteins from resistant and susceptible inbreds revealed that young resistant rachis expresses higher levels of abiotic stress-related proteins such as small heat shock proteins, antioxidant enzymes and enzymes involved in the synthesis of phenolic secondary metabolites. Susceptible young rachis is higher in pathogenesis-related (PR) proteins such as chitinase precursor and glucanase, which are generally inducible upon biotic stress such as pathogen attack.; Response of resistant and susceptible rachis to A. flavus infection seems to be time-dependent. In both young and mature tissues, there were both up- and down-regulated proteins; however, most proteins responded in mature tissues that were under pathogen influence for 35 days. Susceptible rachis showed the most dramatic response by inducing 41 different stress proteins among which 17 were PR proteins. Resistant rachis did not up-regulate PR proteins after infection as these proteins were already high in control samples, where they strongly and constitutively accumulated during maturation. In contrast, susceptible rachis did not accumulate PR proteins to such an extent during maturation, but rather increased them in response to the fungus.; Based on these observations, the model for resistant and susceptible rachis was proposed. |
