Extensin, a major group of the hydroxyproline-rich glycoproteins, are abundant in the plant cell wall. They are rich in hydroxyproline residues which are arranged in many pentapeptide Ser (Hyp)₄ repeats. Extensins are the most well studied, have been implicated in nearly all aspects of plant growth and development including pollen recognition and fe1iilization, cell division and
differentiation, the cessation of cell elongation, in response to pathogen attack and wounding.
However it still remains largely unknown in the exact roles of extensin in plant cell wall. In order to address this question, the overexpressed extensin transgenic Arabidopsis plants were used to infect with the bacterial and fungal pathogens. Pathogenesis analysis within this transgenic line showed that the formation of disease symptoms was restricted by inhibiting the colonization of
the pathogen. Additionally, bacterial defense and signal transduction pathways involved in plant defense were not perturbed in this transgenic line containing the high level of extensin proteins. This is the first study to convincingly
demonstrate a functional linkage between extensin levels and plant resistance to bacterial pathogen invasion.
The expression of the atExt1 gene was investigated by infection with virulent and avirulent bacteria pathogen, which induced the basal defense response and hypersensitive responses marked by activating defense related genes such as PR-1. Northern analysis on the accumulation of atExt1 gene and PR-1 gene showed that the expression patterns of both genes were completely
different, suggesting that the regulation of atExt1 gene was different compared to that of PR-1 gene.
RNA interference (RNAi) is the most widely used approach to identify the gene functions in plant genome. In order to reveal the function of atExt1 gene, the atExt1 coding sequence in sense and antisense orientation was successfully inserted into specific RNA interference (RNAi) vector to produce the most efficient silencing construct. Transgenic Arabidopsis thaliana plants containing
RNAi-atExt1 were generated. Phenotypic analysis of the transgenic plants showed that the lower atExt1 protein levels significantly delayed the different growth stages of Arabidopsis thaliana, in pa1iicularly inhibited inflorescence emergence.