Date Published: October 27, 2016
Publisher: Public Library of Science
Author(s): Mahla Mirali, Randy W. Purves, Rob Stonehouse, Rui Song, Kirstin Bett, Albert Vandenberg, Wei Wang.
The zero-tannin trait in lentil is controlled by a single recessive gene (tan) that results in a phenotype characterized by green stems, white flowers, and thin, transparent, or translucent seed coats. Genes that result in zero-tannin characteristics are useful for studies of seed coat pigmentation and biochemical characters because they have altered pigmentation. In this study, one of the major groups of plant pigments, phenolic compounds, was compared among zero-tannin and normal phenotypes and genotypes of lentil. Biochemical data were obtained by liquid chromatography-mass spectrometry (LC-MS). Genomic sequencing was used to identify a candidate gene for the tan locus. Phenolic compound profiling revealed that myricetin, dihydromyricetin, flavan-3-ols, and proanthocyanidins are only detected in normal lentil phenotypes and not in zero-tannin types. The molecular analysis showed that the tan gene encodes a bHLH transcription factor, homologous to the A gene in pea. The results of this study suggest that tan as a bHLH transcription factor interacts with the regulatory genes in the biochemical pathway of phenolic compounds starting from flavonoid-3’,5’-hydroxylase (F3’5’H) and dihydroflavonol reductase (DFR).
Phenolic compounds are characterized by the presence of at least one -OH group and an aromatic ring. They include phenolic acids, stilbenes, and flavonoids such as flavanones, flavones, dihydroflavonols, flavonols, flavan-3-ols, anthocyanidins, and proanthocyanidins . Phenolics are associated with health benefits including antioxidant activity and protection against diseases such as cardiovascular disorders, cancer, HIV, and diabetes [2–6]. Physical removal of the seed coat of lentils leads to improved iron bioavailability , probably due to the removal of phenolic compounds and the implication that these compounds interfere with iron nutrition .
Phenolic compounds are produced through the actions of numerous regulatory genes and TFs in the phenylpropanoid pathway. These compounds fulfill different roles including seed pigmentation for plants and confer health benefits to humans who eat the seeds [2–6]. We used a combination of biochemical and genetic approaches to investigate the phenylpropanoid pathway to elucidate what is responsible for the lack of seed coat pigmentation in zero-tannin (tan) lentil phenotypes. To accomplish this, we compared seed coats from brown opaque (Ggc Tgc Tan), gray translucent zero-tannin (Ggc tan), and transparent zero-tannin (ggc tan) phenotypes.