Role of Transgrafting in Plant Tolerance to Osmotic Stress
Abiotic stresses, including osmotic stress (OS), significantly limit apple production worldwide. However, limited studies assessed apple rootstocks’ tolerance to osmotic stress. Additionally, the mechanisms by which the tolerant rootstocks improve the tolerance of the scion are largely unknown. It was hypothesized that the tolerance of apple rootstocks is regulated by their responses to OS and that the transgenic rootstock can improve wild-type (WT) scion tolerance through the modulation of the metabolic responses at the physiological, biochemical, and molecular levels. The physiological and molecular responses and their relationships with abscisic acid (ABA) levels were assessed in six apple rootstocks (M26, V3, G41, G935, B9 and B118) which were osmotically stressed with 30% polyethylene glycol (PEG). The results showed that compared to M26 and B118, the rootstocks V3, G41, G935 and B9 demonstrated better tolerance with higher relative water content, higher water use efficiency and lower electrolyte leakage. These differential responses were associated with the ABA content and the expression of some osmotic-responsive genes (ORGs) in the tolerant rootstocks. Furthermore, to investigate the mechanisms underlying the imparted tolerance from the rootstock to the scion, a tomato/potato heterograft model was used to study mRNA transport of some ORGs; where potato was the donor rootstock and tomato was the recipient scion. Of the 21 genes tested under OS, only StNPR1 transcripts were transported across the graft union under both normal and OS conditions. To investigate how the transgenic rootstock affects scion tolerance under OS conditions, the StNPR1 and StDREB1 genes representing the mobile and non-mobile transcripts, respectively, were overexpressed in tobacco (Nicotiana tabacum). The evaluation of transgenic tobacco plants indicated that overexpression of these genes improved the physiological status of transgenic plants growing under OS conditions. Transgenic tobacco rootstocks also increased the OS tolerance of the WT-scion through upregulation of some ORGs transcript levels compared to non-transgenic rootstocks. However, neither StNPR1 nor StDREB1 transcripts were transported from the transgenic rootstock to the WT tobacco scion. This study suggests two candidate genes for future use in transgrafting of tolerant apple rootstocks with specific characteristics to improve plant performance and productivity under OS conditions.
Hezema, Y.S., Shukla, M.R., Goel, A., Ayyanath, M.M., Sherif, S.M., Saxena, P.K. Rootstocks Overexpressing StNPR1 and StDREB1 Improve Osmotic Stress Tolerance of Wild-Type Scion in Transgrafted Tobacco Plants. Int. J. Mol. Sci. 2021, 22, 8398. https://doi.org/10.3390/ijms22168398