In this article we will discuss about the CIS-Acting elements and regulatory role of Dreb-Transcription factors.
The promoter region of almost all stress inducible genes contains two major cis-acting elements. One of the most well characterized stress responsive genes, rd 29A (responsive to dehydration) of Arabidopsis contains two kinds of cis-acting elements in their promoter region. One is the ABA-responsive element (ABRE) and the second is dehydration responsive element (DRE/c-repeat).
ABRE and DRE/CRT are cis-acting elements that function in ABA-dependent and ABA-independent gene expression in response to abiotic stress, respectively. Molecular dissection of rd 29A gene promoter shows well defined DRE-cis element (TACCGACAT) (Fig. 15.3) involved in rapid expression under drought, high-salt and cold stress.
The core sequence of DRE-cis element is CCGAC. This core sequence is found in other stress responsive genes in Arabidopsis, such as rdl7, kin 1, and cor 6.6. A similar motif (c-repeat, TGGCCGAC) has been found in the promoter region of cold-inducible cor 15a gene in Arabidopsis.
It is extremely amazing to see how plant cells sense the water deficiency resulting from various stresses, and how different signals are transmitted which consequently activate DRE- dependent transcription and gene expression of stress relieving genes. Several DRE-binding proteins known as transcription factors (named DREBIA—C, DREB2A—B) specifically participate in the expression of stress-responsive genes.
DREB1A, DREB1B and DREB1C transcription factor genes (generally known as DREB genes) are responsive to cold stress and this can be induced within 10 min under 4°C low-temperature treatment. Similarly, DREB2A was also induced within 10 min when plants are subjected to drought or NaCl high-salt treatment (Fig. 15.4).
All DREB proteins contain a basic region in their N-terminal regions which might function as nuclear localization signal (NLS). In addition, all DREB proteins contain a conserved DNA-binding domain (EREBP/AP2 domain) mainly consist of 58 amino-acid residues.
