The genome of the gymnosperm Picea glauca encodes a single Nucleobase Cation Symporter 1 (PgNCS1) that displays a broad yet unique solute specificity profile

Abstract

The Picea glauca genome contains a locus that encodes for a nucleobase cation symporter 1 (PgNCS1). As a gymnosperm, P. glauca belongs to a key taxonomic position for an ongoing evolution-function analysis of viridiplantae nucleobase cation symporter 1 proteins (NCS1). Here the solute transport and binding properties for PgNCS1 are determined through heterologous expression in Saccharomyces cerevisiae strains deficient in functional NCS1 loci. PgNCS1 displays a broad, yet unique, solute specificity profile –common with other plant NCS1. Yeast containing PgNCS1 transport adenine, guanine, hypoxanthine, xanthine and uracil and are sensitive to growth on 8-azaadenine. Neither cytosine nor 5 flourocytosine are transported by PgNCS1 but along with caffeine and uric acid, act as competitive inhibitors of [3H]-adenine and [3H]-hypoxanthine uptake. This transporter displays high affinity for adenine (Km = 2.67 μM), guanine (Ki = 1.71 μM) and hypoxanthine (Ki = 1.82 μM) but lesser affinity for xanthine (Ki = 5.36 μM). Arabidopsis plants that are deficient in their endogenous NCS1, yet carry PgNCS1, show significant uptake of [3H]-adenine. The results support previous studies and together confirm a broad nucleobase transport and binding pattern for plant NCS1 across the viridiplantae. PgNCS1 displays a broad yet unique nucleosbase transport and binding profile. It transports adenine, guanine, hypoxanthine, xanthine and uracil but only binds cytosine, caffeine, and uric acid.