Functional domain analysis of LmSAP protein reveals the crucial role of the zinc-finger A20 domain in abiotic stress tolerance.

Stress-associated proteins (SAPs), such as A20/AN1 zinc-finger domain-containing proteins, have emerged as a novel class of proteins involved in abiotic stress signaling, and they are important candidates for preventing the loss of yield caused by exposure to environmental stresses. In a previous report, it was found that the ectopic-expression of Lobularia maritima stress-associated protein, LmSAP, conferred tolerance to abiotic and heavy metal stresses in transgenic tobacco plants. This study aimed to investigate the functions of the A20 and AN1 domains of LmSAP in salt and osmotic stress tolerance. To this end, in addition to the full-length LmSAP gene, we have generated three LmSAP-truncated forms (LmSAPΔA20, LmSAPΔAN1, and LmSAPΔA20-ΔAN1). Heterologous expression in Saccharomyces cerevisiae of different truncated forms of LmSAP revealed that the A20 domain is essential to increase cell tolerance to salt, ionic, and osmotic stresses. Transgenic tobacco plants overexpressing LmSAP and LmSAPΔAN1 constructs exhibited higher tolerance to salt and osmotic stresses in comparison to the non-transgenic plants (NT) and lines transformed with LmSAPΔA20 and LmSAPΔA20-ΔAN1 constructs. Similarly, transgenic plants overexpressing the full-length LmSAP gene and LmSAPΔAN1 truncated domain maintained higher superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) enzymatic activities due to the high expression levels of the genes encoding these key antioxidant enzymes, MnSOD, POD, and CAT1, as well as accumulated lower levels of malondialdehyde (MDA) under salt and osmotic stresses compared to NT and LmSAPΔA20 and LmSAPΔA20-ΔAN1 forms. These findings provide insights into the pivotal role of A20 and AN1 domains of LmSAP protein in salt and osmotic stress tolerance.