BREAKING THE TIGHT GENETIC LINKAGE BETWEEN THEa1ANDsh2GENES LED TO THE DEVELOPMENT OF ANTHOCYANIN-RICH PURPLE-PERICARP SUPER-SWEETCORN

Abstract

The existence of purple-pericarp super-sweetcorn based on the most common supersweet mutation, shrunken2 (sh2), has not been previously reported, partly due to its extremely tight genetic linkage to a non-functional anthocyanin biosynthesis gene, anthocyaninless1 (a1). Generally, both aleurone- and pericarp-pigmented purple corn is starchy, the latter of which contains significantly higher anthocyanin compared to the former. The development of purple-pericarp super-sweetcorn is dependent on breaking the a1-sh2 tight genetic linkage, which occurs at a very low frequency of <1 in 1000 meiotic crossovers. Here, to develop purple-pericarp super-sweetcorn, an initial cross between a male purple-pericarp maize (purple-round seed), Costa Rica (A1Sh2.A1Sh2) and a female white shrunken2 super-sweetcorn (white-shrunken seed), Tims-white (a1sh2.a1sh2), was conducted. Subsequent self-pollination based on purple-pericarp-shrunken kernels identified a small frequency (0.08%) of initial heterozygous F3 segregants (A1a1.sh2sh2) producing a fully sh2 cob with a purple-pericarp phenotype, enabled by breaking the close genetic linkage between the a1 and sh2 genes. Resulting rounds of self-pollination generated a F6 homozygous purple-pericarp super-sweetcorn (A1A1.sh2sh2) line, Tim1. Genome sequencing revealed a recombination break between the a1 and yz1 genes of the a1-yz1-x1-sh2 multigenic interval, with the sequence pattern of Tim1 similar to the Costa Rica parent, and after the linkage break, similar to the Tims-white parent. The novel purple-pericarp super-sweetcorn produced a similar concentration of anthocyanin and sugar as in its purple-pericarp maize and white super-sweetcorn parents, respectively, potentially adding a broader range of health benefits than currently exists with standard yellow/white sweetcorn.

Sequence Variations Associated With Novel Purple-Pericarp Super-Sweetcorn Compared to Its Purple-Pericarp Maize and White Super-Sweetcorn Parents

“…The presence of A1 and sh2 has been confirmed by only visual phenotyping. The genetic linkage between them is confirmed by both field observation and genomic analysis (Anirban et al, 2022). However, no genomic information of this novel genotype is available regarding the anthocyanin biosynthesis structural and regulatory genes, along with sweetcorn structural gene.…”

Profiling and Quantification of Anthocyanins in Novel Purple-Pericarp Sweetcorn and Purple-Pericarp Maize

“…Therefore, the kernels are non-purple and shrunken, due to the absence of starch, when fully mature. Recently, a novel purple sh2 sweetcorn was developed from Peruvian purple maize (‘Costa Rica’) and white sh2 sweetcorn (‘Tims-white’) by breaking the extremely tight genetic link between the non-purple a1 and supersweet sh2 genes (Anirban and O’Hare, 2020, Anirban et al, 2022).…”