Key genes needed for maintenance and growth for the two pathogens, Fusarium graminearum and Magnaporthe oryzae, were identified. These are genes that are induced in response to maintenance requirements (stress) and growth requirements. The processes involved are synthesizing arginine, synthesis of DNA-bases, nitric oxide synthesis needing arginine, autophagy, DNA synthesis, and DNA repair. A simplified regulatory network for these key genes for both organisms was constructed as a hypothesis for the work, and procedures previously developed to use sets of downloaded transcriptomic data were used to test hypotheses concerning what time under the course of infection of plants the key genes are expressed. The analysis shows that the transcription efforts (costs) to maintain the fungal cells (maintenance) are high before infection and during early infection. During the following biotrophic stage, maintenance activities drop, followed by a dramatic increase in the necrotrophic stage transition. Finally, in the necrotrophic stage, maintenance is again lower despite the high growth rate that can also cause stress. All identified genes' expressions behaved almost similar with an increased expression in the biotrophy-necrotrophy transition for both fungi except the DNA repair genes PARP/PARG that was not responding or absent (PARG) in the mainly clonal M. oryzae. This PARG expression pattern might indicate that M. oryzae is more subject to evolution by point mutations than F. graminearum, where sexual reproduction is frequent. The potential consequences of this in the development and the accelerated breakage of host species resistance in a Red Queen dynamics scenario are discussed. The analysis demonstrates the possibility of using large transcriptome datasets and co-regulations between key genes to test hypotheses. This technique's advantages complement molecular techniques that employ knockouts and over-expression of target genes to suggest that genes' roles are discussed.