The Content of Anthocyanins in Cowpea (Vigna unguiculata (L.) Walp.) Seeds and Contribution of the MYB Gene Cluster to Their Coloration Pattern

Abstract

The intensively pigmented legumes belonging to Phaseolus and Vigna spp. are valued as an essential component of healthy nutrition due to their high content of flavonoids. In this context, we used the accessions of Vigna unguiculata with different colors of seed coats from the N.I. Vavilov All-Russian Institute of Plant Genetic Resources collection as the main object of this research. We applied confocal laser scanning microscopy, biochemical analysis, and wide in silico and molecular genetic analyses to study the main candidate genes for anthocyanin pigmentation within the MYB cluster on chromosome 5. We performed statistical data processing. The anthocyanin content ranged from 2.96 mg/100 g DW in reddish-brown-seeded cowpea accessions to 175.16 mg/100 g DW in black-seeded ones. Laser microscopy showed that the autofluorescence in cowpea seeds was mainly caused by phenolic compounds. The maximum fluorescence was observed in the seed coat, while its dark color, due to the highest level of red fluorescence, pointed to the presence of anthocyanins and anthocyanidins. Genes of the MYB cluster on chromosome 5 demonstrated a high homology and were segregated into a separate clade. However, amplification products were not obtained for all genes because of the truncation of some genes. Statistical analysis showed a clear correlation between the high content of anthocyanins in cowpea seeds and the presence of PCR products with primers Vigun05g0393-300-1.