Overexpression of ATP binding cassette transporters (ABCs) from Hydrangea macrophylla enhance aluminum tolerance

The ATP-binding cassette (ABC) transporter family represents a large and diverse protein superfamily that plays a crucial role in responding to metal elements stresses. Hydrangea macrophylla is notable for its sepal's bright blue color caused by sequestration of an aluminum (Al) binding pigment in the sepal vacuoles. This allows the species to thrive in acidic soil with high toxic levels of Al. However, the information of ABC family in hydrangea and their roles underlying Al stress are still limited. This study performed a genome-wide characterization, expression analysis and functional assessment of the HmABC family members. The results showed that total 133 HmABC genes were identified from the genome of H. macrophylla 'Bailer', which were classified into eight subfamilies. Furthermore, numerous hormone-response and stress-related promoter cis-acting elements were identified within the HmABC genes. The expansion and duplication of HmABC genes were driven by whole-genome duplication (WGD), segmental duplication, and tandem duplication events. Co-expression analysis identified that 12 ABC members were of hub genes. Expression analysis indicated that these genes were induced in different tissues during Al treatment. Overexpression of certain HmABC genes showed that they can enhance the tolerance of yeast and Arabidopsis to Al by increasing gene expression levels, elevating Al accumulation, and boosting antioxidative enzymatic activities. This discovery lays a foundation for further exploration of the biological functions of HmABCs in hydrangea responding to Al stress, and is helpful for the phytoremediation of acid soils.