Kaempferol over-accumulation in the flavonoid 3’ hydroxylase tt7 mutant disrupts seed coat outer integument differentiation and compromises seed longevity

SUMMARY Seeds slowly accumulate damage during storage, which ultimately results in germination failure. The seed coat is the barrier between the embryo and the external environment, and its composition is critical for seed longevity. Flavonols accumulates in the outer integument, but the effect of altering flavonol composition on outer integument development has not been explored. Genetic, biochemical, ultrastructural and transcriptomics assays on a battery of loss-of-function mutants in the flavonoid biosynthesis pathway were used to study the effect of altered flavonoid composition in seed development and seed longevity. Controlled deterioration assays indicate that loss-of-function of the flavonoid 3’ hydroxylase TT7 gene dramatically affects seed longevity and seed development. Seed outer integument differentiation is compromised from nine days after pollination in tt7 seeds, with a defective suberine layer and incomplete degradation of seed-coat starch. These distinctive phenotypes are not shared by other mutants showing also altered flavonoid composition. Double-mutant analysis indicate that over-accumulation of kaempferol is the primary cause of the observed phenotypes. Expression analysis suggest that the tt7 flavonoid pattern affects transcriptional and non-transcriptional levels of regulation. The increase of kaempferols in the seed coat influences seed development. This positions TT7 as an essential player modulating seed coat development and seed longevity.