Natural Genetic Variation at Tan1 Defines Tannin in Sorghum Grain and Offers Seedling Cold Tolerance

Sorghum, an ancient old-word cereal grass, is the dietary staple of over 500 million people in more than 30 countries of the tropics and semi-tropics. Its C4 photosynthesis, drought resistance, wide adaptation, and high nutritional value hold the promises to alleviate hunger in African populations. Not present in other major cereals such as rice, wheat, and maize, condensed tannin (proanthocyanidin) in the pigmented testa of some sorghum cultivars was implicated in reducing protein digestibility, but recently in promoting human health due to its high antioxidant capacity and fighting obesity due to its digestion reduction. Tannin presence has also been linked to early-season cold tolerance in sorghum. With a combination of genetic tools including quantitative trait locus (QTL) mapping, meta-analysis fine mapping, candidate gene association validation, and gene expression analysis, we showed that natural mutations in the sorghum Tan1 gene, a WD40 protein, control the tannin synthesis and regulate the anthocyanin pathway. One SNP and a second indel in the Tan1 coding region separate the wild-type and mutant haplotypes across diverse sorghum accessions. The sorghum Tan1 gene was transformed into a non-tannin Arabidopsis mutant and restored the wild-type phenotypes. The trait distribution and the molecular diversity analysis of Tan1 in wild sorghums, landraces, and cultivars suggested an incomplete domestication process of sorghum tannin. Genetic dissection of tannin and cold tolerance is being conducted with a set of recombinant inbred lines containing different combinations of Tan1 and Tan2 alleles.