Transcriptional activation of a maize α‐tubulin gene in mycorrhizal maize and transgenic tobacco plants

Abstract

SummaryMycorrhizae are symbioses between soil fungi and roots, with substantial modifications of the cells of both partners, Thus, host cells colonized by mycorrhizal fungi may express otherwise inactive genes. Here it is demonstrated that two arbuscular mycorrhizal (AM) fungi, Glomus versiforme and Gigaspora margarita, cause the transcriptional activation of a gene coding for a-tubulin in the colonized cells of maize and transgenic tobacco roots. Tobacco plants transformed with a construct containing the maize TubG3 gene promoter fused upstream from the bacterial GUS gene showed an intense GUS activity only in meristematic regions. When colonized by G. margarita, GUS activity was detected in the cortical root cells containing fungal arbuscules. No GUS activity was found in root cells when transformants carrying TubG 1 promoter were used, nor when Tub~ 3 transformants were colonized by ericoid mycorrhizal fungi, leading to a non-specific interaction. Activation of the TubG 3 appears to be specific to the gene and to the appropriate interaction. Further evidence that fully differentiated host tissues re-activate the TubG 3 gene following colonization by AM fungi also comes from accumulation of the corresponding transcripts in maize root cells containing arbuscules.

Reorganization of tobacco root plastids during arbuscule development

“…The substructural alterations to a cortical cell during arbuscule formation ± disintegration of the central vacuole, enlargement of the nucleus and its migration towards the center of the cell, respectively, and a general increase in cell organelles ± are features of high metabolic activities. The cellular reorganization of arbuscule-containing cortical cells is, in addition, accompanied by a profound reorganization of the cytoskeleton (Bonfante et al 1996). This feature of high metabolic activities might apply to cells from a suspension culture as well as to cortical cells colonized by a fungal arbuscule and might therefore be the reason for the observed structural similarities.…”

The Cytoskeleton as a Regulator and Target of Biotic Interactions in Plants

“…Increases in expression of tubulin genes and concentrations of plant a-, b-, and g-tubulins and actin have been observed in a variety of ecto-and endomycorrhizas (Bonfante et al, 1996;Diaz et al, 1996;Niini et al, 1996;Timonen et al, 1996;Timonen and Peterson, 2002). Studies of cytoskeletal behavior in ectomycorrhizal associations are limited but suggest that microtubules and actin microfilaments may be largely unaffected by the proximity of intercellular hyphae except, perhaps, in heavily colonized regions where the density of both cytoskeletal arrays was substantially decreased (Timonen et al, 1993;Timonen and Peterson, 2002;Kuga-Uetake et al, 2004).…”

Detection of symbiosis‐related polypeptides during the early stages of the establishment of arbuscular mycorrhiza between Glomus mosseae and Pisum sativum roots

“…A phosphate transporter gene (Harrison & van Buuren, 1995) and a gene homologous to H*-ATPase (Murphy, Langridge & Smith, 1997) were proved to be upregulated in AM symbiosis. Transcriptional activation of a-tubulin gene also occurred in mycorrhizal maize and transgenic tobacco plants symbiosis with AM fungi but are unable to form (Bonfante et al, 1996). Changes in mRNA popu-symbiosis with i^/zz^-o^zMm (myc"*", nod").…”