Innovative mutant screening identifies TRANSPARENT TESTA7 as a player in seed oil/protein partitioning

Brassicaceae species mainly accumulate oil and protein in their seeds, which are essential to human life as a source of food, but also as animal feed and resources for green chemistry. To date, Brassicaceae crops such as rapeseed have been selected mainly for their oil content. However, there is a growing interest in their seed protein content. A strong negative correlation between oil and protein content makes it difficult to increase both compounds simultaneously. In this study, an Arabidopsis thaliana homozygous EMS mutant library was screened by near-infrared spectroscopy for seed oil and protein content, with the aim of identifying mutants with impaired oil-protein correlation. The mutant most affected in this correlation was found to be in the TRANSPARENT TESTA7 gene, which is involved in the flavonoid biosynthetic pathway. Analysis of different mutants in the flavonoid pathway revealed that the tt7 mutants were the only ones to show such a significant reduction in seed oil content, highlighting a phenotype never described before for the tt7 mutants and suggesting a specific role for TT7 in the interplay between the oil and flavonoid biosynthetic pathways. Untargeted metabolomic analysis allowed the identification of metabolic features that are highly accumulated and specific to tt7 seeds compared to the other genotypes and genetic analysis established that the accumulation of kaempferol-3-O-rhamnoside seems to be responsible for the seed oil reduction of tt7 mutants. Significance StatementBrassicaceae species accumulate oil and protein in their seeds and understanding how the partitioning of these compounds is regulated is necessary to engineer seeds for specific purposes. By screening an Arabidopsis EMS mutant library, we identified mutants affected in seed oil/protein partitioning, including tt7, highlighting a link between oil and flavonoid biosynthetic pathways, that we explore further in this paper.