Metabolic profiling and cytological analysis of proanthocyanidins in immature seeds of Arabidopsis thaliana flavonoid accumulation mutants

Kitamura, Satoshi; Matsuda, Fumio*; Toge, Takayuki*; Sakakibara, Keiko*; Yamazaki, Mami*; Saito, Kazuki*; Narumi, Issei

Arabidopsis TT19 encodes a GST-like protein that is involved in the accumulation of proanthocyanidins (PAs) in the seed coat. PA accumulation sites in tt19 immature seeds were observed as small vacuolar-like structures, which show unique thick morphology by differential interference contrast microscopy. The distribution pattern of the thick structures overlapped the location of PA accumulation sites in tt19. Metabolic profiling of the solvent-soluble fraction demonstrated that PA derivatives such as epicatechins and epicatechin oligomers, although highly accumulated in the wild-type, were absent in tt19. We also revealed that tt12 specifically accumulated glycosylated epicatechins, the putative transport substrates for TT12. Given the cytosolic localization of functional GFP-TT19 proteins, our results suggest that TT19, which acts prior to TT12, functions in cytosol for regular accumulation of PA precursors such as epicatechin and glycosylated epicatechin in the vacuole.