Spatial distribution of chitinases and β‐1,3‐glucanase transcripts in bean arbuscular mycorrhizal roots under low and high soil phosphate conditions

Abstract

Arbuscular mycorrhizal (AM) fungi extensively colonize the root cortex under low-soil-phosphate (P) conditions, whereas infection is limited under high-P conditions. Fungal growth under both P conditions might be influenced by plant defence-related gene expression. In this study, we used in situ hybridization methods to compare the cellular localization of three defence-related mRNAs in non-infected bean roots and in relation to fungal infection units. In non-infected and infected roots, mRNAs encoding acidic and basic endochitinases were generally most abundant in the vascular cylinder. High-P-grown mycorrhizal roots showed localized accumulation of the acidic endochitinase mRNA in cortical cells containing arbuscules and in their immediate vicinity (one to five cell layers). The pattern of accumulation of the basic endochitinase mRNA was not affected by P or AM fungal infection. At the low P concentration, the β-1,3-glucanase mRNA accumulated predominantly in the vascular cylinder of noninfected roots. Suppression of β-1,3-glucanase mRNA accumulation in these tissues was observed in non-infected roots at the high-P and in mycorrhizal roots at both P concentrations. The observed suppression extends at least several mm from fungal infection units, characterizing a systemic effect. Beta-1,3-glucanase mRNA accumulated also around a number of cortical cells containing arbuscules only at the low P concentration. The localized accumulations of the endochitinase and β-1,3-glucanase mRNAs suggest that the encoded proteins might be involved in the control of intraradical fungal growth.

Reduced arbuscular mycorrhizal colonization in tomato ethylene mutants

“…In addition, accumulation of transcripts encoding chitinases and β-1,3-glucanases in cells containing arbuscules and their vi- cinity (Lambais & Mehdy, 1998), and suppression of a basic chitinase transcript accumulation in bean mycorrhizal roots, as compared to non-mycorrhizal controls, have been reported (Lambais & Mehdy, 1993). In general, under high P conditions, the expression of these genes is induced or their suppression is attenuated .…”

In silico differential display of defense-related expressed sequence tags from sugarcane tissues infected with diazotrophic endophytes

“…Attenuated suppression, and/or localized induction of DR genes has been observed in mycorrhizal roots grown at conditions unfavorable to the development of the symbioses, e.g. high phosphate concentrations in the soil (Lambais and Mehdy, 1998;Lambais, 2000). Activation of the plant defense system has also been observed in Medicago sativa upon infection with an exopolysaccharide (EPS I)-deficient mutant of Sinorhizobium, suggesting that exopolysaccahrides may act as suppressors of the plant defense system (Niehaus et al, 1993;Gonzalez et al, 1996).…”

Unraveling the signaling and signal transduction mechanisms controlling arbuscular mycorrhiza development

“…Another evidence for this signaling pathway is the reorganization of the microtubule cytoskeleton in cortical cells adjacent to cells containing arbuscules (Blancaflor et al, 2001). The existence of a systemic signal in AM roots-containing arbuscules has also been suggested by Lambais & Mehdy (1998), which showed an induction in the accumulation of transcripts encoding an acidic chitinase in cells containing arbuscules and their immediate vicinity, using in situ hybridization.…”