Interactions of Meristem-Associated Endophytic Bacteria
Generally, all endophytes should be considered as a community that interacts with other symbiotic organisms, such as mycorrhiza. Even though an endophyte may colonize the plant systematically, communities colonizing the plant shoots normally differ to a d
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Interactions of MeristemAssociated Endophytic Bacteria Johanna Pohjanen, Janne J. Koskimäki, and Anna Maria Pirttilä
Abstract
Generally, all endophytes should be considered as a community that interacts with other symbiotic organisms, such as mycorrhiza. Even though an endophyte may colonize the plant systematically, communities colonizing the plant shoots normally differ to a degree from the root-associated endophytes. Meristem-associated shoot endophytic bacteria are often found as contaminants in plant tissue cultures started from shoot tips (buds) or embryos. Whereas root endophytic bacteria are reasonably well studied with respect to location and interactions with the host, not much is known about endophytes associated with shoot meristems. Endophytic bacteria have been localized in the meristematic tissues of buds and flowers by in situ hybridization and transmission electron microscopy. Meristem-associated endophytes may share some growth-promoting traits with the root endophytes, but likely additional mechanisms of actions exist. For example, such endophytes can produce adenine derivatives that induce growth of the host tissue. These endophytes may also affect the plant development by various ways. Some of them can co-synthesize secondary metabolites together with the plant host. Many more mechanisms remain to be determined by methods such as genomics and metabolomics, which are valuable tools for characterizing the interactions between the plant and endophytic bacteria.
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J. Pohjanen • J.J. Koskimäki • A.M. Pirttilä (*) Department of Biology, University of Oulu, PO Box 3000, 90014 Oulu, Finland e-mail: [email protected]
Introduction
The studies on endophytic bacteria are often done on the plant root tissues (Rosenblueth and Martinez-Romero 2006). However, the rootassociated communities typically differ from the shoot-associated ones on their diversity and function (Moore et al. 2006; Mano et al. 2006, 2007;
V.C. Verma and A.C. Gange (eds.), Advances in Endophytic Research, DOI 10.1007/978-81-322-1575-2_5, © Springer India 2014
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Izumi et al. 2008; Yrjälä et al. 2010; Compant et al. 2011). The study by Yrjälä et al. (2010) on hybrid aspen seedlings showed that the most frequently cultured leaf endophyte was Methylobacterium fujisawaense, whereas the roots mainly contained bacterial species of Burkholderia fungorum, Pseudomonas koreensis, and Rahnella aquatilis. Izumi et al. (2008) compared the endophytic populations of pine, birch, and rowan in the belowand aboveground tissues using cultivation-dependent and cultivation-independent analyses. They found a clear difference between the bacterial communities and also showed that a higher number of strains are found in the roots than in the stem and leaf tissues, whereas there was no difference between stem and leaf communities. Cultivation-dependent analyses of grape vine (Compant et al. 2011) and rice (Mano et al. 2006, 2007) have given similar results. In this chapter, the shoot tissues, especially the meristematic tissu
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