A Functional View of Plant Microbiomes: Endosymbiotic Systems That Enhance Plant Growth and Survival
Over the past several decades, it has become clear that numerous nonpathogenic or weakly pathogenic microbes inhabit plants both internally and externally. The challenge for plant biologists who study endophytism lies not only in the discovery of endophyt
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James F. White Jr., Mónica S. Torres, Holly Johnson, Ivelisse Irizarry, and Mariusz Tadych
Abstract
Over the past several decades, it has become clear that numerous nonpathogenic or weakly pathogenic microbes inhabit plants both internally and externally. The challenge for plant biologists who study endophytism lies not only in the discovery of endophytes in plants but also in articulating the precise mechanisms whereby these endophytes function to support the growth and survival of their plant hosts. In this chapter, we discuss the phenomenon of microbial endophytism from a functional perspective. We propose that endophytic microbes in plants comprise a critical part of the plant’s functional systems. We propose three broad categories of endosymbiotic systems, including (1) Defensive Endosymbiotic Systems, (2) Stress Tolerance Endosymbiotic Systems, and (3) Nutritional Endosymbiotic Systems. We will also consider potential interactions between endosymbiotic organisms of plants and relativity of function of endosymbionts. A particular endophyte may serve multiple functions in the ecology of its host plant, and predominant functions of an endophyte may change depending on the ecological circumstances affecting its host. Only now are we beginning to realize how important endophytic microbes are to plants. Much research is needed to elucidate the mechanisms of action and the roles that endophytes play in modulating host plant ecology and enhancing plant growth and survival.
1 J.F. White Jr. (*) • M.S. Torres • I. Irizarry • M. Tadych Department of Plant Biology and Pathology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901, USA e-mail: [email protected] H. Johnson Department of Computer Science, Central Washington University, Ellensburg, WA, USA
Introduction
Since the development of the germ theory, most scientists, working with plant- and animalinfecting microbes, have focused their research efforts on microbes that cause disease (Ainsworth 1981). Endophytes (fungi and/or bacteria that live within tissues of plants) largely appear to be the inverse of plant pathogens since generally
V.C. Verma and A.C. Gange (eds.), Advances in Endophytic Research, DOI 10.1007/978-81-322-1575-2_21, © Springer India 2014
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they represent cryptic benign infections of healthy plants. Although we cannot cite any statistics, experience with endophytic microbial populations in plants suggests that they outnumber plant pathogens many times to one (Bills 1996; Suryanarayanan et al. 1998; Arnold et al. 2001). Recent diversity studies of microbial endophytes would seem to support this view (Arnold et al. 2001; West et al. 2010; Lucero et al. 2011; Porras-Alfaro and Bayman 2011; Zimmerman and Vitousek 2012). In fact, endophytism is so common among microbes (as compared to pathogenicity) that it may well be that endophytism is the normal state for most plantinfecting microbes and pathogenicity is the “out-of-balance” condition (Schulz and Boyle 2005). In this chapter, we discus
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