Abstract
Drought stress conditions in soil or air hinder plant growth and development. Here, we report that the hot pepper (Capsicumannuum) RING type E3 Ligase 1 gene (CaREL1) is essential to the drought stress response. CaREL1 encodes a cytoplasmic- and nuclear-localized protein with E3 ligase activity. CaREL1 expression was induced by abscisic acid (ABA) and drought. CaREL1 contains a C3H2C3-type RING finger motif, which functions in ubiquitination of the target protein. We used CaREL1-silenced pepper plants and CaREL1-overexpressing (OX) transgenic Arabidopsis plants to evaluate the in vivo function of CaREL1 in response to drought stress and ABA treatment. CaREL1-silenced pepper plants displayed a drought-tolerant phenotype characterized by ABA hypersensitivity. In contrast, CaREL1-OX plants exhibited ABA hyposensitivity during the germination, seedling, and adult stages. In addition, plant growth was severely impaired under drought stress conditions, via a high level of transpirational water loss and decreased stomatal closure. Quantitative RT-PCR analyses revealed that ABA-related drought stress responsive genes were more weakly expressed in CaREL1-OX plants than in wild-type plants, indicating that CaREL1 functions in the drought stress response via the ABA-signalling pathway. Taken together, our results indicate that CaREL1 functions as a negative regulator of ABA-mediated drought stress tolerance.
Highlights
Plants are sessile organisms, and they frequently encounter various stress conditions such as high light, extreme temperature, and water stress
We investigated whether Capsicumannuum RING type E3 Ligase 1 gene (CaREL1) has E3 ligase activity by conducting an in vitro self-ubiquitination assay with maltose-binding protein tagged CaREL1 (MBP::CaREL1)
Several studies have reported that abscisic acid (ABA)-signalling components, which function as positive or negative regulators of abiotic stress responses, are ubiquitinated and degraded by E3 ubiquitin ligase and 26S proteasome, respectively[30, 31]
Summary
They frequently encounter various stress conditions such as high light, extreme temperature, and water stress. A large number of stress-related genes involved in these defence mechanisms are regulated by ABA4. Ubiquitin is composed of 76 amino acids and contains seven lysines that serve as the site of modification[12] Ubiquitination via these enzymes conjugates single or multiple ubiquitins to the target proteins, which are recognized by the 26S proteasome for degradation. CaREL1-silenced pepper plants exhibited an ABA-hypersensitive phenotype with significantly enhanced tolerance to drought stress. CaREL1-OX Arabidopsis plants exhibited an ABA-insensitive and drought-sensitive phenotype characterized by a high transpiration rate and altered expression levels of stress-related genes. Our findings indicate that the CaREL1 RING type E3 ligase negatively regulates drought stress tolerance via the ABA-signalling pathway
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