Characterization of the ABC Transporter G Subfamily in Pomegranate and Function Analysis of .

ATP-binding cassette subfamily G (ABCG) proteins play important roles in plant growth and development by transporting metabolites across cell membranes. To date, the genetic characteristics and potential functions of pomegranate ABCG proteins (PgrABCGs) have remained largely unknown. In this study, we found that 47 PgrABCGs were divided into five groups according to a phylogenetic analysis; groups I, II, III, and IV members are half-size proteins, and group V members are full-size proteins. , , and were highly expressed in the inner seed coat but had very low expression levels in the outer seed coat, and the expression levels of these three genes in the inner seed coats of hard-seeded pomegranate 'Dabenzi' were higher than those of soft-seeded pomegranate 'Tunisia'. In addition, the expression of these three genes was highly correlated with the expression of genes involved in lignin biosynthesis and hormone signaling pathways. The evolution of presents a highly similar trend to the origin and evolution of lignin biosynthesis during land plant evolution. Ectopic expression of in promoted plant growth and lignin accumulation compared to wild type plants; meanwhile, the expression levels of lignin biosynthesis-related genes (, , and ) and cytokinin response marker genes ( and ) were significantly upregulated in transgenic plants, which suggests the potential role of in promoting plant growth and lignin accumulation. Taken together, these findings not only provide insight into the characteristics and evolution of s, but also shed a light on the potential functions of s in seed hardness development.