ABSTRACT
Plant-microbe interactions are vital to agricultural and plant productivity, which in turn have a direct and significant influence on the diversity, nature, and activity of colonizing microbial communities. Enzymes play a key role in these interactions and consequently have been the subject of intense interest. The main focus has been at the soil-plant interface (the rhizosphere), but plant litter decomposition is also of major importance. The ecological characteristics, ecosystem function, and mechanistic approaches to the study of phytopathogenicity all have aspects that involve enzymes. These subject areas are dealt with elsewhere in this volume (see Chapter 7). In this chapter, we concentrate on the interplay of microorganisms, how “cross-talking” and the regulation of gene expression influence the enzymes they produce, and how such processes influence community succession and functional diversity. We intend to draw on the limited data available to describe microorganisms that colonize the surface of leaves and, to a lesser extent, the inner tissues and other aerial parts of the plant such as the stems, fruits, flowers, and woody tissue (the phyllosphere). The chapter has been organized to describe the physical and chemical nature of the habitat, and the type and survival strategies of colonizing microbial populations. We discuss the nature and role of enzymes that have evolved to provide the genotypic and phenotypic plasticity necessary for microorganisms to survive under the selective pressures of this extreme habitat. The chapter is completed by discussion of developments in methodology that recently have become available to investigate the role and potential activity of enzymes in what can be extreme conditions, and the potential for their biotechnological exploitation.
