Roles of the Histone Acetyltransferase Rtt109 in Genome Integrity Maintenance of Magnaporthe oryzae

Abstract

Preservation of genome integrity is undoubtedly a fundamental function of life, ensuring the survival and propagation of specific genetic assemblages selected over time. The fungal-specific histone acetyltransferase Rtt109 is implicated in various chromatin functions influencing genome integrity and plasticity. In particular, Rtt109 plays a crucial role in nucleosome assembly associated with DNA replication and repair processes. This thesis explores the implications of Rtt109-mediated genome integrity maintenance in the plant pathogen Magnaporthe oryzae, regarding pathogenicity and mycological development. Deletion of Rtt109 led to a marked decrease in mycelial growth rate and a concomitant growth reduction in planta. The growth defect seems to be linked to the elevated level of DNA damage constitutively suffered by the mutant, even in the absence of genotoxins. Accordingly, expression of DNA damage repair genes and stress-related genes were increased. The deletion mutant was also rendered hypersensitive to various forms of genotoxic stress including ROS, which is integral to fungal morphogenesis and the plant defense response. However, appressorium morphogenesis was unaffected by the absence of Rtt109 and the extent of growth reduction in planta was not beyond the innate mycelial growth defect. Therefore it is considered that the level of ROS and genotoxic stress experienced by M. oryzae during interaction with the host plant is not sufficient to hinder infectious development, even in the vulnerable state without Rtt109. Furthermore, it can be inferred that the intrinsic protective mechanisms together with the up-regulation of DNA damage and stress response genes may be sufficient to protect the mutant throughout the lifecycle. In conclusion, Rtt109-mediated genome preservation is required for normal growth and genotoxic stress resistance in M. oryzae. Although Rtt109 is not directly involved in pathogenicity, it is expected to have important contributions to genome regulation and evolution.