Identification and Functional Analysis of cis-Regulatory Elements in Salicornia brachiata SbPIP2 Promoter Under Abiotic Stress

This study aims to elucidate the regulatory role of the Salicornia brachiata aquaporin gene (SbPIP2) promoter, in response to abiotic stress in plants. Through computational analysis, we identified an array of cis-regulatory elements within the 1800 bp SbPIP2 promoter region. To functionally characterize this promoter, we constructed five sequential deletions and two specific deletions targeting the ABRE and AS-1 elements, and fused them to a GUS reporter gene. Quantitative GUS assays revealed a 5.7-fold increase in expression under abiotic stress conditions for the full-length promoter. Compared to the CaMV 35S promoter, the SbPIP2 promoter showed half the expression levels under unstressed conditions, but displayed a three-fold increase under abiotic stress. Deletion of ABRE and AS-1 elements confirmed their roles in elevated promoter activity and stress responsiveness, respectively. Additionally, quantitative MUG assays highlighted the presence of tissue-specific repressor sites between positions − 1027 to − 707 in the stem and root. Our findings provide critical insights into the SbPIP2 promoter's architecture and function, and identify key motifs for targeted manipulation to enhance abiotic stress tolerance in crops. This work contributes substantially to our understanding of molecular mechanisms in plant stress responses, setting the stage for the development of more resilient agricultural systems in the context of climate change.