Genetics and Biochemistry of the Low Tannin Characteristic in Vicia faba L. and Development of a Molecular Marker for the zt2 Gene
Zanotto, Stefano 1992-
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Faba bean is a cool season grain legume which is grown in many areas of the world. It is used either as a food or feed and it has the highest concentration of protein in the seed compared to all the other pulses. The presence of condensed tannins (proanthocyanidins) in the testa of the seeds limits the use of faba bean both in the food and feed industries. Low tannin faba bean varieties are available for cultivation. The low tannin phenotype is controlled by two genes zt1 and zt2. Low tannin plants also have completely white flowers. The presence of either of the genes in the recessive form is sufficient for determining the low tannin and white flower phenotype. The main objective of this project was to develop and validate a molecular marker for the zt2 gene. A set of 875 SNP markers physically anchored to the genome of Medicago truncatula was used to genotype a RIL population at the F6 segregating for zt2. One of the SNP markers, located 10.5 cM from zt2, successfully discriminated the genotypes carrying the recessive (zt2) allele from those carrying the dominant (ZT2) allele. The SNP marker was then converted to KASP assay format. The second objective of this study was to test the available molecular tools for tagging the zt1 and zt2 genes for their efficacy in identifying the genotypes carrying the recessive alleles at both zt1 and zt2 loci. The F2:3 population segregating for both low tannin genes were used for this purpose. The KASP marker for the zt2 gene was again successful in distinguishing the recessive (zt2) allele from the dominant (ZT2) allele. For the zt1 gene we used two SCAR markers, SCG111171 and SCC5551 that are publicly available. Only SCC5551 was partially effective in tagging the zt1 gene. This marker in combination with the zt2 KASP marker may be used in future research aiming at the identification of the double recessive genotype zt1zt2. The third objective of the research was to analyze the phenolic profiles of the seed coats and flowers of three faba bean genotypes, one wild type and two low tannin lines recessive for either zt1 or zt2. For these analyses we used LC-MS techniques, covering over 100 known phenolic compounds. The results suggested a possible point of action of the zt genes in the flavonoid biosynthetic pathway. The results also showed clear differences in the phenolic profiles between the two low tannin lines both in the seed coats and the flowers. Furthermore, one unknown compound present in only one of the two low tannin lines was characterized, matching its MS/MS spectrum with that of a compound previously identified in another species. This and other compounds could be used as biochemical markers to distinguish the zt1 from the zt2 genotypes. In conclusion, this study enhanced our knowledge on the mode of action of the two low tannin genes zt1 and zt2, linking the results from molecular analysis with those at the biochemical level. The study successfully developed a molecular marker for the zt2 gene which could be used in combination with biochemical markers by plant breeders targeting the low tannin phenotype in their breeding programs.
DegreeMaster of Science (M.Sc.)
SupervisorTar'an, Bunyamin; Vandenberg, Albert
CommitteeLamb, Eric; Tyler, Robert; Yuefeng, Ruan
Copyright DateAugust 2018