Extensins are hydroxyproline-rich glycoproteins that are abundant in the cell walls of higher plants. In this work, the function and regulation of one of the extensin genes (atExtl) of the model plantArabidopsis thaliana L. was studied.
In order to discover the function of the atExtl protein, transgenic A. thaliana
plants were generated containing the atExtl coding sequence under the
transcriptional control of the strong constitutive CaMV 35S promoter.
Hydroxyproline assays showed that transgenic plants which over-expressed atExtl contained higher levels of hydroxyproline-rich protein compared to the wild-type controls. Phenotypic analysis of the transgenic plants showed that higher atExtl protein levels stimulated the cessation of stem elongation and caused a reduction in overall plant height. This is the first time that a causal relationship between extensin expression and plant phenotype has been demonstrated.
The regulation of the atExtl gene was investigated by the generation of
transgenic A. thaliana plants containing a series of 5' promoter truncations fused to the GUS reporter gene. Seven truncations were constructed, terminating at -110, - 412, -883, -1226, -1747, -1963 and-2209bp upstream of the translation start site.
Histochemical analysis of the transgenics identified promoter regions involved in
root-specific and seedling-specific expression, as well as induction by insect
herbivory, mechanical stress, pathogen attack and treatment with salicylic acid and methyl jasmonate. Further studies have also shown that at least four regions of the atExtl promoter interact in a complex manner to regulate the response of the plant to wounding.
Sequence analysis of the atExtl gene promoter has identified a large number of
putative cis-acting motifs based on their similarity to known plant transcription factor binding sites. Possible roles for these elements in the regulation of the atExtl gene are discussed.