Overexpression of ZxABCG11 from Zygophyllum xanthoxylum enhances tolerance to drought and heat in alfalfa by increasing cuticular wax deposition

Drought and heat stresses cause yield losses in alfalfa, a forage crop cultivated worldwide. Improving its drought and heat tolerance is desirable for maintaining alfalfa productivity in hot, arid regions. Cuticular wax forms a protective barrier on aerial surfaces of land plants against environmental stresses. ABCG11 encodes an ATP binding cassette (ABC) transporter that functions in the cuticular wax transport pathway. In this study, ZxABCG11 from the xerophyte Zygophyllum xanthoxylum was introduced into alfalfa by Agrobacterium tumefaciens-mediated transformation. Compared to the wild type (WT), transgenic alfalfa displayed faster growth, higher wax crystal density, and thicker cuticle on leaves under normal condition. Under either drought or heat treatment in greenhouse conditions, the plant height and shoot biomass of transgenic lines were significantly higher than those of the WT. Transgenic alfalfa showed excellent growth and 50% greater hay yield than WT under field conditions in a hot, arid region. Overexpression of ZxABCG11 up-regulated wax-related genes and resulted in more cuticular wax deposition, which contributed to reduction of cuticle permeability and thus increased water retention and photosynthesis capacity of transgenic alfalfa. Thus, overexpression of ZxABCG11 can simultaneously improve biomass yield, drought and heat tolerance in alfalfa by increasing cuticular wax deposition. Our study provides a promising avenue for developing novel forage cultivars suitable for planting in hot, arid, marginal lands.