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ISHS Acta Horticulturae 834: III International Late Blight Conference

THE REGULATION OF SPORULATION-SPECIFIC TRANSCRIPTION IN PHYTOPHTHORA INFESTANS

Authors:   Qijun Xiang, H.S. Judelson
Keywords:   asexual development, sporangia, promoter, transcription factor binding site, potato late blight
Abstract:
The asexual sporangia produced by P. infestans play an important role in spreading disease. Prior microarray analyses identified numerous genes specifically expressed during sporulation that may provide insight into this important pathway. This study focuses on identifying the transcription factor binding sites (TFBS) in promoters of those genes, and the matching transcription factors. The promoters of two genes (Cdc14 and Pks1) were characterized in detail. The Cdc14 promoter contains three tandemly repeated 9-bp motifs with the consensus YCTYAACVS. This apparent TFBS determines not only the strength of sporulation-specific transcription, but also the specificity of the site of transcription initiation. Electrophoretic mobility shift assays (EMSA) indicate that the nuclear protein binding to the motif requires at least two adjacent repeats and the AACV bases are critical for binding. By following the DNA-binding activity in chromatographic separations, we are purifying the putative transcriptional regulator. The Pks1 promoter also contains several putative TFBSs based on functional analyses and assays for protein-binding activity. One may involve two tandem repeats of the sequence CGTTG, which is significantly enriched in promoters expressed preferentially in sporangia. In conclusion, our research indicates that sporulation-specific promoters contain diverse regulatory modules. This may reflect the complex spatial and temporal patterns of gene expression that are required to form sporangia, to prepare them for germination and infection structure development, and to satisfy the nutritional and metabolic needs of sporangia prior to germination.
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