Mutations of two AhTT8 genes reduce the accumulation of anthocyanins and confer the white testa of peanut (Arachis hypogaea L.).

Anthocyanins and proanthocyanidins (PAs), which determine the color of peanut seed coats, not only offer protection to plants under biotic and abiotic stress but also contribute to human health. The white testa peanut contains lower levels of anthocyanins and PAs, yet the mechanisms underlying the white testa phenotype in peanuts remain largely unknown. In the current study, two homologous peanut AhTT8 genes, namely AhTT8_AA and AhTT8_BB, were identified as the key genes controlling the seed coat color of peanuts through BSA-seq analysis and fine mapping. Null mutations or long sequence insertions were observed in two AhTT8 genes across six cultivated peanut varieties with white seed coat, and expression of AhTT8 genes was downregulated significantly in the white seed coat of peanuts. Overexpression of AhTT8 successfully restored PA and anthocyanin productions in Arabidopsis thaliana tt8 mutant. Furthermore, transcriptomic profiling of the seed coats of pink testa peanuts and white testa peanuts showed that expression of genes encoded transcription factors like AhMYB5, AhTTG1, AhMYB1, AhCPC, AhTTG2 and AhGL2 was downregulated in the white seed coats, while a subset of genes involved in PA and anthocyanin biosynthesis were also downregulated in the white seed coats. These results indicated that AhTT8 plays a central role in the regulation of peanut PA and anthocyanin biosynthesis, and resolving the molecular mechanisms of AhTT8 in peanuts is of great significance for peanut molecular breeding.