Transcription factor binding is regulated by several interactions, primarily involving cis-element binding. These binding sites maintain specificity by means of their sequence, and other additional factors such as inter-motif distance and spacer specificity. The ACGT core sequence has been established as a functionally important cis-element which frequently regulates gene expression in synergy with other cis-elements. In this study, we used two monocotyledonous – Oryza sativa and Sorghum bicolor, and two dicotyledonous species – Arabidopsis thaliana and Glycine max to analyze the conservation of co-occurring ACGT core elements in plant promoters with respect to spacer distance between them. Using data generated from Arabidopsis thaliana and Oryza sativa, we also identified conserved regions across all spacers and possible conditions regulating gene promoters with multiple ACGT cis-elements.

Gene expression is mediated through interaction between cis regulatory elements and its cognate transcription factors. Cis regulatory elements are defined as non-coding DNA sequences that provide the binding sites for transcription factors and are clustered in the upstream region of genes. ACGT cis regulatory element is one of the important cis regulatory elements found to be involved in diverse biological processes like auxin response, salicylic acid response, UV light response, ABA response and jasmonic acid response .We identified through in silico analysis that the upstream region of protein phosphatase 2C (PP2C) gene has a distinct genetic architecture of ACGT elements. In the present study, the activation of the full length promoter and its deletion constructs like 900 base pair, 500 base pair, 400 base pair and NRM were examined by stable transformation in Arabidopsis thaliana using β glucuronidase as the reporter gene. Evaluation of deletion constructs of PP2C- like promoter was carried out in the presence of phytohormones like abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA). Our result indicated that the full length and 900 base pair promoter-reporter constructs of PP2C-like promoter was induced in response to ABA but not to methyl jasmonate and salicylic acid.

Transcription control of gene expression depends on a variety of interactions mediated by the core promoter region, sequence specific DNA-binding proteins, and their cognate promoter elements. The prominent group ofcisacting elements in plants contains an ACGT core. Theciselement with this core has been shown to be involved in abscisic acid, salicylic acid, and light response. In this study, genome-wide comparison of the frequency of occurrence of two ACGT elements without any spacers as well as those separated by spacers of different length was carried out. In the first step, the frequency of occurrence of theciselement sequences across the whole genome was determined by using BLAST tool. In another approach the spacer sequence was randomized before making the query. As expected, the sequence ACGTACGT had maximum occurrence inArabidopsis thalianagenome. As we increased the spacer length, one nucleotide at a time, the probability of its occurrence in genome decreased. This trend continued until an unexpectedly sharp rise in frequency of (ACGT)N25(ACGT). The observation of higher probability of bigger size motif suggests its directed evolution inArabidopsis thalianagenome.