Ectopic expression of an apple ABCG transporter gene MdABCG25 increases plant cuticle wax accumulation and abiotic stress tolerance

A number of enzymes and transcription factors involved in cuticular wax biosynthesis have been identified in plenty of plant species. The pathway of wax biosynthesis is relatively definite. The molecular basis of cuticular wax deposition is still unclear, especially the transport mechanism of cuticular wax from endoplasmic reticulum (ER) to the cell wall. It has been found that ABCG transporter family is involved in wax export process in some model plants. However, whether ABCG transporters participate in wax transport in apple is unknown. In this study, MdABCG25, encoding an ABCG transporter, was isolated from apple (Malus domestica Brokh.). MdABCG25, containing an AAA domain and an ABC2_membrane domain, is highly expressed in apple pericarp and induced by drought, salt and ABA conditions. The heterologous expression of MdABCG25 in Arabidopsis leads to an increasing cuticular wax accumulation of stems and leaves. The epidermal permeability, water loss rate and chlorophyll extraction rate of MdABCG25 transgenic Arabidopsis were decreased. The expression of MdABCG25 improved the drought and salt tolerance of apple calli and Arabidopsis.