Basic leucine zipper transcription factor SIbZIP1 mediates salt and drought stress tolerance in tomato

Background: Basic region/leucine zipper (bZIP) transcription factors perform as crucial regulators in ABA-mediated stress response in plants. Nevertheless, the functions for most bZIP family members in tomato remain to be deciphered. Results: Here we examined the functional characterization of SIbZIP1 under salt and drought stresses in tomato. Silencing of SIbZIP1 in tomato resulted in reduced expression of multiple ABA biosynthesis- and signal transduction-related genes in transgenic plants. In stress assays, SIbZIP1-RNAi transgenic plants exhibited reduced tolerance to salt and drought stresses compared with WT plants, as are evaluated by multiple physiological parameters associated with stress responses, such as decreased ABA, chlorophyll contents and CAT activity, and increased MDA content. In addition, RNA-seq analysis of transgenic plants revealed that the transcription levels of multiple genes encoding defense proteins related to responses to abiotic stress (e.g. endochitinase, peroxidases, and lipid transfer proteins) and biotic stress (e.g. pathogenesis-related proteins) were downregulated in SIbZIP1-RNAi plants, suggesting that SIbZIP1 plays a role in regulating the genes related to biotic and abiotic stress response. Conclusions: Collectively, the data suggest that SIbZIP1 exerts an essential role in salt and drought stress tolerance through modulating an ABA-mediated pathway, and SIbZIP1 may hold potential applications in the engineering of salt- and drought-tolerant tomato cultivars.