Characterization of anthocyanin production in maize germplasm

Anthocyanins are the visually appealing red-orange to blue natural pigments present in most plant species. Because of their ease of aqueous extraction and rich color, anthocyanins make suitable natural replacements for synthetic dyes like FD&C Red 40. Increasing consumer demand for natural ingredients in foods and beverages has justified a search for more economic sources of natural colorants. Maize has been used a natural source of color for centuries. South American cultures in particular use purple corn varieties termed “Maize Morado” in foods and beverages. Maize has economic potential as a value-added source of natural colors. To characterize the diversity of anthocyanin production in maize germplasm, 398 diverse accessions of pigmented maize were analyzed with High Performance Liquid Chromatography (HPLC). To the best of our knowledge, this is the largest collection of pigmented maize investigated for anthocyanin diversity and composition. A subset of this collection was also used to test the repeatability of anthocyanin content and composition in several environments. Within the collection, 167 accessions could produce detectable amounts of anthocyanins. Clusters of accessions were created based on the abundance of pigments in the aleurone or pericarp layers and on compositional variations. These clusters were confirmed by principal component analysis and hierarchical clustering. Pericarp-pigmented accessions that could produce flavanol-anthocyanin dimers called “condensed forms” were the most important accessions in the survey in terms of total anthocyanin content. In the survey acylated anthocyanins were typically the most predominant pigments types, except in a few unique lines that only produce cyanidin 3-glucoside as their major pigment. The hypothesis tested was that this trait is due to partial loss of function anthocyanin acyltransferase. To characterize this phenotype, coined the “reduced acylation” trait, a mapping population was created from a mutant phenotype line crossed to B73, the reference genome. Genotyping-by-sequencing was used to generate single nucleotide polymorphisms that could be used to map the location of the trait in the maize genome. QTL analysis found one significant loci at the end of chromosome 1 which corresponds to a candidate anthocyanin acyltransferase GRMZM2G387394. A UniformMu Mu transposon knockout of this gene maintained the phenotype when crossed to reduced acylation mutants meaning the gene is responsible for a majority of the anthocyanin acyltransferase activity in maize. Overall, information provided here will assist plant breeders looking to develop anthocyanin-rich purple corn hybrids as a source of natural colorants for food and beverages