Global Patterns of Gene Regulation Associated with the Development of Ectomycorrhiza Between Birch (Betula pendula Roth.) and Paxillus involutus (Batsch) Fr.

Abstract

The formation of ectomycorrhizal (ECM) root tissue is characterized by distinct morphological and developmental stages, such as preinfection and adhesion, mantle, and Hartig net formation. The global pattern of gene expression during these stages in the birch (Betula pendula)-Paxillus involutus ECM association was analyzed using cDNA microarrays. In comparison with nonsymbiotic conditions, 251 fungal (from a total of 1,075) and 138 plant (1,074 in total) genes were found to be differentially regulated during the ECM development. For instance, during mantle and Hartig net development, there were several plant genes upregulated that are normally involved in defense responses during pathogenic fungal challenges. These responses were, at later stages of ECM development, found to be repressed. Other birch genes that showed differential regulation involved several homologs that usually are implicated in water permeability (aquaporins) and water stress tolerance (dehydrins). Among fungal genes differentially upregulated during stages of mantle and Hartig net formation were homologs putatively involved in mitochondrial respiration. In fully developed ECM tissue, there was an upregulation of fungal genes related to protein synthesis and the cytoskeleton assembly machinery. This study highlights complex molecular interactions between two symbionts during the development of an ECM association.

PtSRR1, a putative Pisolithus tinctorius symbiosis related receptor gene is expressed during the first hours of mycorrhizal interaction with Castanea sativa roots

“…However, most of the differentially expressed fungal genes were observed in later stages of symbiotic development, especially after two or more days of interaction (3,6,9), which is corroborated by the 12 h PtSRR1 transcription. Therefore, the high relative expression of PtSRR1 at 12 h favours its investigation.…”

“…Several stages of the ectomycorrhiza formation and maintenance processes from preinfection to the formation of the mantle and the Hartig net have been described, and it is obvious that changes in gene expression have to accompany the processes leading to symbiosis (6,8).…”

Paxillus involutus Forms an Ectomycorrhizal Symbiosis and Enhances Survival of PtCOMT-modified Betula pendula in vitro

“…In the ECM symbiosis, on the other hand, the defence responses are thought to be weak or only transient (HAHN and MENDGEN, 2001). In a recent microarray assay of B. pendula-P. involutus ECMs, expression of the precursor genes of lignin biosynthesis, CCoAOMT (caffeoyl-coenzyme A 3-Omethyltransferase) and SAD (sinapyl alcohol dehydrogenase), as well as a gene homolog to a dirigent protein, were induced in specific developmental phases of ECMs (LE QUÉRÉ et al, 2005). This indicates that lignin biosynthesis may also be involved in the formation of the ECM association.…”

“…is a common ECM fungus forming a symbiosis with a large number of tree species including Betula pendula. In the ECM symbiosis between P. involutus and B. pendula (BRUN et al, 1995;LE QUÉRÉ et al, 2005) lateral roots are rapidly enclosed by the hyphal mantle and thus isolated nutritionally from the soil. In addition, the hyphae penetrate between epidermal cells and form a highly branched Hartig net at the nutrient exchange interface.…”

“…During mycorrhiza formation the epidermal cells of lateral roots extend radially, which has been suggested to increase the surface contact between the symbionts (BRUN et al, 1995). The distinct stages in the ECM development between B. pendula and P. involutus are covered by numerous changes in gene expression in both symbionts (JOHAN-SSON et al, 2004;LE QUÉRÉ et al, 2005;MOREL et al, 2005), including the genes related to lignin biosynthesis in B. pendula (LE QUÉRÉ et al, 2005).…”