Characterization of tt15, a novel transparent testa mutant of Arabidopsis thaliana (L.) Heynh.

The Arabidopsis thaliana seed coat typically has a brown color due to the accumulation of flavonoid pigments in the testa. Mutants of A. thaliana with defects in pigment biosynthesis often produce seeds that are olive brown or even yellow in appearance, and the responsible genetic loci are referred to as TRANSPARENT TESTA (TT). Large-scale screening for mutants affected in seed development and complementation analysis of a candidate mutant line with all published A. thaliana tt mutants identified a new tt locus designated tt15. The tt15 mutation maps to the lower part of chromosome 1. Mutant plants produced pale greenish-brown seeds whose dormancy was slightly reduced. The phenotype was consistent with the maternal origin of the testa. Analysis of pigment accumulation and the study of expression patterns of genes involved in flavonoid biosynthesis in tt15 plants and seeds indicated a seed-specific phenotype. Most notable was a reduction of the cyanidin and quercetin content of tt15 seeds.