Poster: Late and Moved Abstracts
Abs #
1395: EST sequencing and elicitor-responsive gene expression in hybrid poplar
Plant defense against pests and pathogens is a very active process. Little is known about inducible defenses in trees, where mechanisms and signaling pathways leading to defense responses may differ from those in herbaceous species. In most plants, a rapid response to pathogen attack is the induction of signaling and defense related genes. We have used different elicitor treatments to trigger defense mechanisms in hybrid poplar plants and cell cultures in order to analyze gene expression profiles. Elicitation with salicylic acid (SA), benzothiadiazol (BTH), and other elicitors led to rapid accumulation of marker gene transcripts. The kinetics and levels of gene expression differed among the various elicitors, and these different responses were also reflected in distinct pH changes in the culture medium. BTH, an SA analogue, triggered expression of a pathogenesis-related gene PR1 but did not effect extracellular pH. By contrast, SA induced wound-responsive genes such as phenylalanine ammonia lyase and a trypsin inhibitor, and caused strong transient medium alkalinization. To further investigate the differences among defense pathways and to identify novel genes potentially involved in defense, five suppression subtractive hybridization (SSH) libraries were constructed for expressed sequence tag (EST) sequencing. Comparison with sequence databases revealed that these SSH libraries are enriched in clones with putative defense roles. However, the most frequent ESTs differed markedly among the libraries, providing indirect evidence of differential gene expression. DNA microarrays are being constructed to enable simultaneous high-throughput gene expression analyses to further investigate the diversity of defense responses in hybrid poplar.
