Overexpression of the pear PbSPMS gene in Arabidopsis thaliana increases resistance to abiotic stress

The fruit of ‘Dangshansuli’ pear is yellowish green in colour, while that of its mutant ‘Xiusu’ is russet in colour. A differentially expressed gene, PbSPMS, was screened from the transcriptomes of the exocarps of ‘Dangshansuli’ and ‘Xiusu’ fruit. To understand the role of PbSPMS in the russet exocarp formation of ‘Xiusu’, the expression of the PbSPMS gene in the exocarp of ‘Dangshansuli’ and ‘Xiusu’ at different stages of development was analysed. The functions of the PbSPMS gene in phenolic synthesis and suberin and polyamine (PA) deposition in Arabidopsis plants and the responses to drought and salt stress were also studied. The results showed that the relative area of vascular bundles of the transgenic PbSPMS Arabidopsis plants was larger than that of the wild-type (WT) plants and that the secondary thickened cell wall of the xylem was thicker in the transgenic Arabidopsis plants than in the WT plants. The contents of PAs, phenolics and suberin in the PbSPMS Arabidopsis plants were greater than those in the WT plants. Under drought and salt stress, the introduction of PbSPMS facilitated the rapid accumulation of spermidine (Spd) and spermine (Spm) within a short period of time in A. thaliana, and the contents of Spd and Spm were significantly greater in the transgenic plants than in the WT plants, showing that PbSPMS participates in the stress response rapidly to reduce the negative effects of stress. Moreover, exogenous PbSPMS increased the contents of proline (Pro), H2O2, peroxidase (POD) and soluble sugars in the plants. With prolonged stress time, the contents of all the compounds increased gradually, and the longer the stress time was, the more significant the drought resistance of the PbSPMS transgenic plants. Overall, the results demonstrated that PbSPMS contributes to phenolic synthesis and suberin and PA deposition in Arabidopsis plants and improves plant resistance to both drought and salt stress.