Pennycooke, Joyce C , Cheng, Hongmei , Stockinger, Eric J .
Comparative genomic sequence of downstream targets of Medicago CBF transcription factors reveals clusters of functional cis-acting low temperature regulatory elements 2kbp upstream of the coding sequences.
Medicago truncatula, an annual of Mediterranean origin and alfalfa, M. sativa subsp. falcata, a perennial of wide geographic adaptation were compared for their capacity to cold acclimate and in elements of the cis/trans regulatory system of the CBF transcriptional activators. Freezing tolerance studies indicated that M. truncatula survived to about - 5 oC but unlike alfalfa did not substantially increase in freezing tolerance after a period of cold treatment. Cold acclimation specific CAS15 transcripts were induced in both spp while CAS17 transcripts were not expressed in M. truncatula. Alignment of the genomic sequence containing CAS15 revealed a highly conserved region more than 2kb upstream of the coding sequence separated from the coding sequence by a region of non-identity. Within this upstream region was an island of CRT/DRE and ABRE motifs found to be essential for cold induced CAS15 expression. Similarly, in CAS17 the distal upstream region was conserved and separated from the coding sequence and the adjacent promoter region by a stretch of non-identical nucleotides. This also revealed that the CAS17 genes encode much larger polypeptides than previously thought and were renamed MfCAS30 and MtCAS31 accordingly. Functional analyses of the homologous MfCAS30 and MtCAS31 regions immediately upstream of the coding sequence indicated that MfCAS30 had the necessary elements to confer low temperature responsiveness while MtCAS31 did not. However addition of the MfCAS30 distal region with multiple pairs of closely spaced CRT/DRE motifs to the MtCAS31 proximal promoter imparted low temperature responsiveness. From these experiments we conclude that regions distal to the coding sequence are critical for low temperature induced CAS expression in Medicago species.
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1 - The Ohio State University / OARDC, Horticulture and Crop Science, 1680 Madison Ave, Wooster, OH, 44691, USA
comparative functional genomics
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM