Identification of the function of mutualistic root endophytic fungi using an Arabidopsis transcriptome model system
mutualistic fungi are important determinants of many ecosystem functions
because they control community dynamics and net primary productivity of
their host plants (Hartnett
and Wilson 1999; Newsham et al. 1995). Mycorrhizal fungi are an abundant and relatively well-understood group
of such mutualists. Our recent observations challenge the overwhelming
abundance of the mycorrhizal root symbionts: non-mycorrhizal endophytes in
Konza Prairie Long Term Ecological Research site equal or exceed the
mycorrhizal fungi in abundance. During
experiments aiming to determine the host ranges of these endophytes, we
discovered that at least two of the endophyte species form functional
mutualisms with Arabidopsis thaliana
and increase the host’s growth two- to four-fold. This finding is novel: A.
thaliana does not associate with mycorrhizal fungi and there is only one
prior example of endophyte associations in A.
et al. 2004; Smith and Read 1997). We aim to take advantage of this unique and fortuitous mutualism to
further understand the function of root-associated symbioses. This system is
broadly applicable to root symbioses and the wealth of information available
for A. thaliana will allow
advances in understanding mycorrhizal and non-mycorrhizal root symbioses
alike. Our primary hypotheses are that, similar to mycorrhizal systems, root
endophyte colonization will 1) induce a systemic host defense improving the
plant resistance against pathogens; 2) improve host nutrient metabolism;
and, 3) improve host water use efficiency and drought tolerance. We are
testing these hypotheses in experiments using A.
thaliana mutants deficient in defense signaling pathways, in experiments
using A. thaliana and Botrytis
cinerea-pathogen system as well as in experiments where water
availability to endophyte-colonized and non-colonized A.
thaliana plants is controlled and the plant growth and fitness measured.
We also plan to include analyses of differential up- and downregulation of
distal gene expression in endophyte-colonized and endophyte-free hosts using
an Affymetrix ATH1 array for A.
Hartnett DC, Wilson GWT (1999) Mycorrhizae influence plant community structure and diversity in tallgrass prairie. Ecology 80:1187-1195
Newsham KK, Fitter AH, Watkinson AR (1995) Multi-functionality and biodiversity in arbuscular mycorrhizas. TREE 10:407-411
Peskan-Berghöfer T, Shahollari B, Giong PH, Hehl S, Markert C, Blanke V, Kost G, Varma A, Oelm¨ller R (2004) Association of Piriformospora indica with Arabidopsis thaliana roots represents a novel system to study beneficial plant-microbe interactions and involves early plant protein modifications in the endoplasmic reticulum and at the plasma membrane. Physiologia Plantarum 122:465-477
Smith SE, Read DJ (1997) Mycorrhizal symbiosis. Academic Press, London