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, 38 (3), 354-61

Expression and Regulation of the Arabidopsis Thaliana Cel1 Endo 1,4 Beta Glucanase Gene During Compatible Plant-Nematode Interactions

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Expression and Regulation of the Arabidopsis Thaliana Cel1 Endo 1,4 Beta Glucanase Gene During Compatible Plant-Nematode Interactions

Serenella Sukno et al. J Nematol.

Abstract

The root-knot nematode Meloidogyne incognita is an obligate endoparasite of plant roots and stimulates elaborate modifications of selected root vascular cells to form giant cells for feeding. An Arabidopsis thaliana endoglucanase (Atcel1) promoter is activated in giant cells that were formed in Atcel1::UidA transgenic tobacco and Arabidopsis plants. Activity of the full-length Atcel1 promoter was detected in root and shoot elongation zones and in the lateral root primordia. Different 5' and internal deletions of regions of the 1,673 bp Atcel1 promoter were each fused to the UidA reporter gene and transformed in tobacco, and roots of the transformants were inoculated with M. incognita to assay for GUS expression in giant cells and noninfected plant tissues. Comparison of the Atcel1 promoter deletion constructs showed that the region between -1,673 and -1,171 (fragment 1) was essential for Atcel1 promoter activity in giant cells and roots. Fragment 1 alone, however, was not sufficient for Atcel1 expression in giant cells or roots, suggesting that cis-acting elements in fragment 1 may function in consort with other elements within the Atcel1 promoter. Root-knot nematodes and giant cells developed normally within roots of Arabidopsis that expressed a functional antisense construct to Atcel1, suggesting that a functional redundancy in endoglucanase activity may represent another level of regulatory control of cell wall-modifying activity within nematode feeding cells.

Figures

Fig. 1
Fig. 1
Schematic representation of Atcel1 promoter-UidA constructs in transformed tobacco plants analyzed for tissue expression and response to nematode infection. A) The full-length 1,673 bp Atcel1 promoter, B-F) 5’ Atcel1 promoter deletion constructs harboring different lengths of the promoter (serial B and C, internal D, E, and F). Numbers indicate the length in bp of the respective promoter regions. Coding region of the β-glucuronidase gene. TSP transcription starting point, 1 to 4 indicate respective excised promoter regions.
Fig. 2
Fig. 2
Histochemical staining for GUS activity in transgenic tobacco plants containing the Atcel1 promoter infected by the root-knot nematode, Meloidogyne incognita. A) Atcel1-driven GUS expression in a 7-day-old uninfected tobacco root. B) Atcel1-driven GUS expression in a shoot tip of a young uninfected tobacco seedling. C) Atcel1 promoter deletion construct B (harboring a 502 bp 5’ deletion, promoter fragment 1)-driven GUS expression in the shoot elongation zone of an uninfected tobacco plant. No activity is detectable in the roots. D) Whole-mount histochemical GUS assay of a Cel1-transgenic tobacco plant infected with M. incognita. Atcel1 activity is confined to the nematode feeding cells (not shown) and the plant elongation/ differentiation zones. A = shoot meristem (Construct B shown). E) Atcel1-driven GUS expression within M. incognita-induced giant cells four days post-inoculation of nematodes to an Atcel1-GUS transgenic tobacco root (construct A, Fig. 1). GUS activity is confined to the central region of the developing gall tissue. F) Sections (30 μm thick) through M. incognita-infected Atcel1-GUS tobacco roots after GUS staining. GUS expression is restricted to the giant cells induced by the nematode. N = nematode, GC = giant-cells,
Fig. 3
Fig. 3
Putative cis-acting elements of the Atcel1 promoter as predicted by the Plant-CARE (Lescot et al., 2002), PLACE (Higo et al., 1999; Rombauts et al., 2003), and MOTIF SAMPLER (Thijs et al., 2001) algorithms. The transcription start point (TSP) is indicated with +1: transcription start point. Distances in bp are relative to the translation start codon.
Fig. 4
Fig. 4
Constitutive expression of antisense Atcel1 in transgenic A. thaliana and infection of these plant roots with the root-knot nematode, M. incognita. A) Both shoot and root development of Atcel1 antisense (ANTI) plants are compromised as compared to wild-type (WT) Arabidopsis. B) Giant cells (GC) form normally around the head of a developing root-knot nematode (N) in a (10-μm-thick) cross- section of a wild-type Arabidopsis root. C) Giant cell and nematode development in antisense Atcel1 Arabidopsis progress normally even as root and shoot development are compromised. Abbreviations are defined in the text and in Table 2.

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