Overexpression of ShCHL P in tomato improves seedling growth and increases tolerance to salt, osmotic, and oxidative stresses

Geranylgeranyl reductase (CHL P) catalyzes the reduction of geranylgeranyl diphosphate to phytyl diphosphate and provides phytol for both chlorophyll (Chl) and tocopherol (TP) synthesis. Our previous study has found that the Solanum habrochaites CHL P (ShCHL P) gene was repressed by cold stress. In this study, we functionally characterized this gene with respect to abiotic stress tolerance. ShCHL P is expressed highly in leaves and stems, and barely in roots. Also, its expression was suppressed by low and high temperatures, drought, salt, and oxidative stresses. Transgenic tomato plants overexpressing ShCHL P showed increased levels of Chl and alpha-TP in leaves. In contrast, Chl and alpha-TP contents were reduced in the co-suppression plants, which exhibited chlorosis. These results confirmed the previous findings that CHL P is essential for Chl and TP synthesis in plants. Moreover, the ShCHL P overexpression and suppression lines showed improved and inhibited early seedling growth under normal, salt, and osmotic stress conditions, respectively, as compared with the wild type. Surprisingly, both overexpression and suppression of CHL P in transgenic tomato enhanced tolerance to methyl viologen-induced oxidative stress. These results indicate that tomato CHL P plays an important role in response to abiotic stress through regulation of Chl and TP synthesis. CHL P might be a good candidate gene for genetic improvement of plant growth under abiotic stress conditions in tomato.