Characterization and diagnostic marker for TTG1 regulating tannin and anthocyanin biosynthesis in faba bean

Abstract

Condensed tannins, found in coloured-flowering varieties of faba bean (Vicia faba L) are, after vicine and convicine, one of the major anti-nutritional factors for monogastric animals. The development of tannin-free cultivars is a key goal in breeding to broaden the use of this legume in the animal feed industry. Two recessive genes, zt-1 and zt-2, control the zero-tannin content and promote white-flowered plants. Previous studies exploiting synteny with the model Medicago truncatula reported a mutation in TTG1, a gene encoding a WD40 transcription factor located in chromosome II, as the responsible for the zt-1 phenotypes. Here a comprehensive analysis of VfTTG1 (including phylogenetic relationships, gene structure and gene expression) has been conducted to confirm the identity of the gene and to reveal structural changes that may result in different functional alleles. The results confirmed the identity of the candidate and revealed the existence of two different alleles responsible for the phenotype: ttg1-a, probably due to a mutation in the promoter region, and ttg1-b caused by a deletion at the 5′end of VfTTG1. Based on the sequencing results, an allele-specific diagnostic marker was designed that differentiate zt-1 from wild and zt-2 genotypes and facilitates its deployment in faba bean breeding programs.

A bHLH transcription factor (VfTT8) underlieszt2, the locus determining zero tannin content in faba bean (Vicia faba L.)

“…Previous studies ascribed this locus to the distal part of chr. III 26,28,29 . The last authors also reported a KASP marker (SNP marker Vf_Mt7g100500_001), 10.5 cM far from flower colour, as a successful marker to discriminate low tannin plants although the closest flanking marker (Vf_Mt1g072740_001), 3 cM apart, failed to distinguish contrasted genotypes in the validation panel 29 .…”

“…The approach ascribed the target zt2 region in the distal part of faba bean chr. III between the ESTs markers Pis-Gen-8-1-1 and LG38 26,28 . Using the sequence information deposited in the M. truncatula Genome Database (MTGD) (http://www.medicagogenome.org/), these genes corresponded to…”

“…The approach allows us to assign the target loci to the distal part of the chr. III 26,28 . Upon confirmation of the chromosomal region containing the flower colour locus, the next step was to exploit the extensive collinearity with Medicago to saturate the target region and mine candidate genes associated with the trait.…”

“…Our results provide new insights on the regulatory mechanisms for tannin biosynthesis in faba bean and will favour the development of an ultimate zt2 diagnostic marker for the fast generation of new value-added cultivars free of tannins and improved nutritional value.Recently, an ortholog of the Medicago WD40 transcription factors, Transparent Testa Glabra 1 (TTG1) in the faba bean chromosome (chr.) II, has been reported as the gene encoding the zt1 phenotypes [25][26][27][28] . Likewise, the locus zt2 was found to be in the distal part of the chr.…”

“…Recently, an ortholog of the Medicago WD40 transcription factors, Transparent Testa Glabra 1 (TTG1) in the faba bean chromosome (chr.) II, has been reported as the gene encoding the zt1 phenotypes [25][26][27][28] . Likewise, the locus zt2 was found to be in the distal part of the chr.…”