Fungal Gene Expression and Interaction With Host Plants

Abstract

Plants may be affected by a wide range of diseases, the majority of which can result in significant economic losses. To survive biotic stresses, plants use their inherent or acquired immune systems to resist pathogen invasion. The interactions between plants and diseases are complex, which initiate once they contact each other. The genes for host resistance and pathogen virulence or avirulence must be recognized by precise observation of the initial infection stage. The results of these observations will help researchers direct their efforts toward crop breeding for resistance or facilitate understanding and working on the pathogenesis of fungi. For sustainable crop production, it is important to work on the interaction of cross-species due to the development of resistance against fungicides. Phytopathogenic fungi utilize plants as hosts to cause infection, resulting in huge economic losses. Plants, unlike animals, are immobile; thus, they are highly dependent upon their immune response, either innate or systemic acquired, to escape pathogen invasion. In addition to the immune response, immediately after the plant perceives the pathogen on its surface, it evolves various biochemical mechanisms, such as secretion of proteins or phosphorylation of different kinases, activating several signaling pathways to evade biotic stress. On the other hand, the fungus has its own mechanism to thrive on plants. Obligate fungi utilize plant machinery throughout their life cycle, while the necrotrophic ones survive on living or dead organic matter. Non-obligate fungi require plants to sustain a particular period of their life cycle, while necrotrophic fungi choose to escape host resistance by either killing the host or secreting lytic enzymes or toxins. The fungal infection process initiates with the adherence of the spore to the host surface, followed by germination and penetration through the epidermis or the tiny stomatal openings or plant wounds, and later followed by haustorium development, absorption of nutrients, and spread of the hyphae on host tissues. Certain chemical and physical signals, such as appressoria induction, and the development of structures that can easily penetrate the plant epidermal layer are also involved. Various mechanisms operate during the establishment of a fungal pathogen on the host plant surface, which include the initiation of signaling pathways, production of reactive oxygen species, influx of ions, and phosphorylation of proteins. For each gene responsible for virulence in fungal pathogens, a gene is responsible for resistance in the host plant. A very fine understanding of the mechanism involved in plant–pathogen interaction at the cell genomic level is unraveled. This chapter will focus on the expression of fungal genes during host plant infection and unravel the mechanisms involved.