TRANSPARENT TESTA10 Encodes a Laccase-Like Enzyme Involved in Oxidative Polymerization of Flavonoids in Arabidopsis Seed Coat

Abstract

The Arabidopsis thaliana transparent testa10 (tt10) mutant exhibits a delay in developmentally determined browning of the seed coat, also called the testa. Seed coat browning is caused by the oxidation of flavonoids, particularly proanthocyanidins, which are polymers of flavan-3-ol subunits such as epicatechin and catechin. The tt10 mutant seeds accumulate more epicatechin monomers and more soluble proanthocyanidins than wild-type seeds. Moreover, intact testa cells of tt10 cannot trigger H 2 O 2 -independent browning in the presence of epicatechin and catechin, in contrast with wild-type cells. UVvisible light detection and mass spectrometry revealed that the major oxidation products obtained with epicatechin alone are yellow dimers called dehydrodiepicatechin A. These products differ from proanthocyanidins in the nature and position of their interflavan linkages. Flavonol composition was also affected in tt10 seeds, which exhibited a higher ratio of quercetin rhamnoside monomers versus dimers than wild-type seeds. We identified the TT10 gene by a candidate gene approach. TT10 encodes a protein with strong similarity to laccase-like polyphenol oxidases. It is expressed essentially in developing testa, where it colocalizes with the flavonoid end products proanthocyanidins and flavonols. Together, these data establish that TT10 is involved in the oxidative polymerization of flavonoids and functions as a laccase-type flavonoid oxidase.

Gene Expression and Metabolite Profiling of Developing Highbush Blueberry Fruit Indicates Transcriptional Regulation of Flavonoid Metabolism and Activation of Abscisic Acid Metabolism

“…polymerization (Pourcel et al, 2005). We also detected flavonols in placentae and the seed coat, and in the epidermal layer of the seed coat there appeared to be a redistribution of flavonols toward the cell periphery in early seed development.…”

PROTEIN l-ISOASPARTYL METHYLTRANSFERASE2 Is Differentially Expressed in Chickpea and Enhances Seed Vigor and Longevity by Reducing Abnormal Isoaspartyl Accumulation Predominantly in Seed Nuclear Proteins

“…The accumulation of antioxidant components like tocopherols, tocotrienols, flavonoids, and a number of antioxidative enzymes was shown to be important in maintaining seed vigor and viability (Bailly, 2004). The contribution of testa to seed longevity was also shown by various studies (Debeaujon et al, 2000;Pourcel et al, 2005). Desiccation tolerance and seed longevity in orthodox seeds were also shown to be associated with the presence and abundance of specific proteins like late embryogenesis abundant proteins or heat shock proteins (Blackman et al, 1995;Wehmeyer and Vierling, 2000).…”

A Key Role for Apoplastic H2O2 in Norway Spruce Phenolic Metabolism

“…3; Supplemental Fig. S2B; Pourcel et al, 2005Pourcel et al, , 2007. As peroxidase action is essential in the formation of high-molecular-weight lignin polymer in this cell culture and polymers were not formed in the presence of KI, the involvement of another type of oxidative enzyme is likely.…”