The TRANSPARENT TESTA12 gene of Arabidopsis encodes a multidrug secondary transporter-like protein required for flavonoid sequestration in vacuoles of the seed coat endothelium

Phenolic compounds that are present in the testa interfere with the physiol ogy of seed dormancy and germination, We isolated a recessive Arabidopsis m utant with pale brown seeds, transparent testa12 (tt12), from a reduced see d dormancy screen. Microscopic analysis of tt12 developing and mature teste s revealed a strong reduction of proanthocyanidin deposition in vacuoles of endothelial cells. Double mutants with tt12 and other testa pigmentation m utants were constructed, and their phenotypes confirmed that tt12 was affec ted at the level of the flavonoid biosynthetic pathway. The TT12 gene was c loned and found to encode a protein with similarity to prokaryotic and euka ryotic secondary transporters with 12 transmembrane segments, belonging to the MATE (multidrug and toxic compound extrusion) family. TT12 is expressed specifically in ovules and developing seeds. In situ hybridization localiz ed its transcript in the endothelium layer, as expected from the effect of the tt12 mutation on testa flavonoid pigmentation. The phenotype of the mut ant and the nature of the gene suggest that TT12 may control the vacuolar s equestration of flavonoids in the seed coat endothelium.