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rd29A Stress Induced Promoter

Plants experience a wide range of abiotic stresses due to their sessile nature. Plants have evolved many biochemical responses to stresses that range from cold and drought to salinity and osmotic factors. Substantial research has revealed a complex network of genes that work together during stress conditions. A key player in the abiotic stress response in Arabidopsis is DREB1 (Dehydration Response Element Binding Protein) a family of three related (A, B, C) transcription factors that bind to DRE (Dehydration Response Element), a cis-acting element that functions in ABA-independent gene expression, specifically as an up regulator of rd29A. Researchers have demonstrated that rd29A is up regulated in response to salt, drought and cold conditions (Shinozaki, 1998).

Plant cold stress responses in Arabidopsis have been shown to contain several pathways that are specific to abiotic stresses. The DREB1 family has been shown to be most strongly expressed in response to cold stress, salinity, osmotic, and drought stresses. Specifically, DREB1C has been shown to be most active in cold stress response, while DREB1A and DREB1B show expression patterns in drought and salinity as well (Yamaguchi-Shinozaki, 2009). Promoter regions for the three DREB1 proteins contain six homologous sequences, or boxes, that correspond to specific binding motifs. While the specific mechanism of cold induction is not yet clear, DREB1C promoter analysis has shown MYB, and MYC binding sequences(Shinozaki, 1998)as well as evidence that the CAMTA3, calcium dependent protein, is involved in up regulation of the cold response (Thomashow, 2009).

While DREB1C up regulation shows significant increase in plant cold tolerance, an over expression results in dwarfism and stunted growth. It has been shown that PIF7, a Phytochrome interacting factor (PIF) which is integral to circadian rhythm controls, act as a daytime inhibitor of DREB1C (Yamaguchi-Shinozaki, 2009). This helps mitigate damage from over expression by acting as one of many counter regulatory elements.

These genes have also been shown to have orthologs in rice and maize, OsDREB1A and ZmDREB1A respectively. Expression of these gene constructs in transgenic Arabidopsis showed increased tolerance to cold, salt, and drought stresses. While these genes do not bind all target DREB1 sequences, they show expression patterns that mimic Arabidopsis (Yamaguchi-Shinozaki, 2006).

The DREB1C promoter could be combined with a reporter gene to serve as a valuable biosensor for cold induced stresses. The fact that it is up regulated by cold stress (MYB and MYC binding motifs) (Shinozaki, 1998) but down regulated by circadian controls (PIF7 binding) (Yamaguchi-Shinozaki, 2009) allow for a more accurate warning when particular plants were under cold stress while keeping constitutive levels low. Evidence that it shares expression orthologs in some plants hints that the DREB1C promoter could be adapted to fit many crop types.