Bacterial Endophytes: Who and Where, and What Are They Doing

Diverse bacteria known as endophytes inhabit virtually all plants. Endophytic bacteria are referred to as those that can be detected at a particular moment within the tissues of apparently healthy plant hosts (Hallmann et al. 1997; Schulz and Boyle, 2006). Most of the endophytes colonize different compartments of the plant apoplast, including the intercellular spaces of the cell walls and xylem vessels. Some of them are able to colonize reproductive organs of plants, for example flowers, fruits, and seeds. Inside a plant these bacteria do not normally cause any substantial morphological changes like root-nodule symbionts do (see Chapters 44, 45). They also do not cause any disease symptoms, in contrast to phytopathogens. Many endophytic bacteria possess a number of plant-beneficial traits in vitro; few of those are exhibited in planta and only a small number of endophytes proved to be very effective plant growth-promoting and/or biocontrol agents under agricultural conditions (Scherwinski et al., 2008; Berg, 2009; see Chapters 53, 54).
In the following paragraphs we 07111 discuss a number of important issues about endophytes. We 07111 begin with a description of which bacteria were found as endophytes. Subsequently, colonization strategies used by endophytes 07111 be described. How do they get inside plants? Which molecular traits are important for endophytic colonization? How do they escape the р1а111’5 Immune response? Once they establish themselves in a plant, some endophytes can have a number of beneficial effects on their hosts. What are the mechanisms of their beneficial influence on plants? Here we will focus on those …