Overexpression of the Arabidopsis H+-PPase enhanced resistance to salt and drought stress in transgenic alfalfa (Medicago sativa L.)

Salinity and drought are two major abiotic factors limiting crop production. To generate the legume forage adapting to saline and arid soils, we had transformed alfalfa (Medicago sativa) with AVP1, a vacuolar H+-pyrophosphatase (H+-PPase) gene from Arabidopsis thaliana. In this paper, we report that overexpression of the AVP1 gene confers enhanced salt and drought tolerance to the transformed alfalfa. Transgenic alfalfa grows well in the presence of 200 mM NaCl and also under a water-deprivation condition, while wild-type plants exhibit chlorosis and growth inhibition, even death. Compared with wild-type plants, transgenic plants accumulate more Na+, K+ and Ca2+ in leaves and roots. Moreover, the leaves of transgenic plants retain more water during drought stress than those of wild-type plants due to lower solute potential. Increased solute accumulation and water retention, and steady intracellular ion homeostasis might also confer other phenotypes of salt and drought tolerance in the transgenic plants, which include the higher photosynthesis capacity and the lesser cell membrane damage during salt or water-deficit stress. Furthermore, the increased potassium uptake and root activity in transgenic alfalfa may be the consequences of rhizosphere acidification resulting from expression of the AVP1. These results indicated that the expression of AVP1 confers enhanced salt and drought tolerance on alfalfa, a very important crop. This study provides a way for improving salt and drought tolerance in important legume forages.