Understanding the mechanism of abiotic-tolerance and producing germplasm of abiotic tolerance are important in plant research. Wild species often show more tolerance of environmental stress factors than their cultivated counterparts. Genes from wild species show potential abilities to improve abiotic resistance in cultivated species. Here, a tomato proline-, lysine-, and glutamic-rich type gene SpPKE1 was isolated from abiotic-resistant species (Solanum pennellii LA0716) for over-expression in tomato and tobacco for salt tolerance. The protein encoded by SpPKE1 was predominantly localized in the cytoplasm in tobacco. SpPKE1 and SlPKE1 (from cultivated species S. lycopersicum cv. M82) shared 89.7% similarity in amino acid sequences and their transcripts abundance in flowers and fruits was reduced by the imposition of drought or oxidative stress and the exogenous supply of abscisic acid. The DNA of the PKE1 promoter was highly methylated in fruit and leaf, and the methylation of the coding sequence in leaf was significantly higher than that in fruit at different development stages. The over-expression of SpPKE1 under the control of a CaMV (Cauliflower Mosaic Virus) 35S promoter in transgenic tomato and tobacco plants enhanced their tolerance to salt stress. PKE1 was downregulated by abiotic stresses but enhanced the plant's salt stress tolerance. Therefore, this gene may be involved in post-transcriptional regulation and may be an important candidate for molecular breeding of salt-tolerant plants.
Keywords: abiotic stress; proline-, lysine-, and glutamic-rich protein; salt stress; tobacco; wild tomato species.