Phenylalanine ammonia lyase (PAL) plays a major role in plant growth, development and adaptation. In Arabidopsis thaliana, the enzyme is encoded by four genes, namely PAL1, PAL2, PAL3, and PAL4 with PAL1 and PAL2 being closely related phylogenetically and functionally. PAL1 promoter activities are associated with plant development and are inducible by various stress agents. However, PAL2 promoter activities have not been functionally analysed. Here, we show that the PAL2 promoter activities are associated with the structural development of a plant and its organs. This function was inducible in an organ-specific manner by the avirulent strain of Pseudomonas syringae pv. tomato (JL1065). The PAL2 promoter was active throughout the course of the plant development particularly in the root, rosette leaf, and inflorescence stem that provide the plant with structural support. In aerial organs, the levels of PAL2 promoter activities were negatively correlated with relative positions of the organs to the rosette leaves. The promoter was inducible in the root following an inoculation by JL1065 in the leaf suggesting PAL2 to be part of an induced defence system. Our results demonstrate how the PAL2 promoter activities are being coordinated and synchronised for the structural development of the plant and its organs based on the developmental programme. Under certain stress conditions the activity may be induced in favour of certain organs.
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Acknowledgments This work was supported by a grant to Dr Mohd Puad Abdullah from the Research University Grant Scheme (RUGS) Initiative 4 Project No. 02-02-07-0328RU, Universiti Putra Malaysia (UPM). We thank Prof Maznah Ismail of the Institute of Bioscience UPM for allowing us to use some of the facilities in the Laboratory of Molecular Biomedicine, Prof Tan Soon Guan and Dr Noor Baity Saidi of the Department of Cell and Molecular Biology, UPM for proofreading and commenting on the manuscript.
- Phenylalanine ammonia lyase
- Phenylpropanoid pathway
- Promoter activities
- Pseudomonas syringae pv. tomato