Study On The Enhancement Of Drought And Salt Tolerance Of Tall Fescue (Festuca Arundinacea Schreb) By Over-expressing ZmPIS

Drought and salinity stress is detrimental for the growth and development of plants, resulting in the slow growth or even death of crops. Plants have developed many complicated mechanisms in response to the drought and salinity injury in the course of evolution through a variety of signaling pathways. Previous studies have indicated that phosphoinositide-signaling pathways play key roles in plant growth, development and response to environmental stresses. Phosphatidylinositol (PtdIns) is synthesized from CDP-DG and myo-inositol, catalyzed by phosphatidylinositol synthase (PIS), and is one of the most important phospholipids and a major precursor of molecules involved in phosphoinositide-signaling pathways. Tall fescue (Festuca arundinacea Schreb) is a perennial, cool-season grass species widely used for forage and turf with a heterologous hexaploid genome. It is widely maintained on lawns and public grounds for the characters of resistance to cold, heat and diseases. In this research, ZmPIS, cloned from Maize, was transformed into tall fescue and transgenic lines were used for experiments for drought or salinity stress tolerance determination, in order to reveal the impact of heterologous overexpression of ZmPIS on physiological and developmental changes of tall fescue, thus obtaining new breeding materials which present tolerance to drought and salinity stresses, with potential in the tall fescue genetic breeding.In this research, ZmPIS cDNAs were introduced into tall fescue using Agrobacterium-mediated transformation method in sense and antisense forms. The transgenic events were identified by PCR and Southern blotting analysis, showing the integration of ZmPIS gene into the tall fescue genomes. Then, the sterile single buds derived from multiple shoot clumps of transgenic and non-transgenic tall fescue plants were subcultured on MS medium supplemented with mannitol or NaCl. The results indicated that the lines expressing sense ZmPIS gene showed significant better growth and proliferation capacity than the wild-type, and those expressing antisense ZmPIS gene showed similar growth and proliferation capacity as the WT.The drought tolerance of transgenic tall fescues plants in pots was measured. Three lines expressing sense ZmPIS gene, one expressing antisense ZmPIS gene and the WT were selected, for each of the three genotypes, and treated by withholding water at the same time to determine the changes of physiological parameters. Under drought stress condition, most transgenic lines expressing sense ZmPIS gene had more biomass and better growth than WT, also they had higher relative water content and chlorophyll content in leaves, and less membrane damage and lipid peroxidation than WT, showing much better drought tolerance than WT. Those expressing antisense ZmPIS gene showed similar results as the WT. It is deduced that plants of these sense lines had lower solute potential than those of antisense lines and WT, protecting plants from drought stress induced injury. Overall the results suggested that the over-expression of ZmPIS in tall fescue enhanced the drought tolerance of transgenic plants.During salinity stress treatment, transgenic and WT tall fescue seedlings grown in pots full of sand were subjected to salinity stress by watering sufficient Hoagland nutrient solution adding 350 mM NaCl everyday to allow drainage at the bottom of the pots. 15 days later, the shoots of antisense line and the WT withered and turned yellow, partly due to the higher environmental temperature, but the tillers of some sense lines were still green and alive all the time. Most sense lines had higher proline and chlorophyll content, and less MDA content, implying less lipid peroxidation, than WT, while there was no significant difference between those of the antisense line and the WT. The better salt-tolerance of the sense transgenic lines might be due to the retain of more solutes including proline in cells, which would benefit the capability of water uptake at low soil solution water potential to reduce the level of salt stress injury.In summary, the results of drought and salinity stress experiments indicated that over-expression of ZmPIS in tall fescue significantly improved the salt and drought tolerance of transgenic plants. These salt and drought-tolerant lines are of value in drought and salt-tolerant tall fescue breeding, thereby make contributions to tall fescue production and utilization of large area of arid and saline-alkali soils in China. Also, the results obtained here open up a way for a better understanding of the relationship between plant adaptation to osmotic stress and phosphatidylinositol signal pathway.