A Maternally Deposited Endosperm Cuticle Contributes to the Physiological Defects of transparent testa Seeds

Mature dry seeds are highly resilient plant structures where the encapsulated embryo is kept protected and dormant to facilitate its ultimate dispersion. Seed viability is heavily dependent on the seed coat9s capacity to shield living tissues from mechanical and oxidative stress. In Arabidopsis (Arabidopsis thaliana) the seed coat, also called testa, arises after differentiation of maternal ovular integuments during seed development. We recently described a thick cuticle tightly embedded in the mature seed9s endosperm cell wall. We show here that it is produced by the maternal inner integument 1 layer (ii1) and, remarkably, transferred to the developing endosperm. Arabidopsis transparent testa (tt) mutations are a class of maternally-inherited mutations causing seed coat pigmentation defects. TT gene products encode proteins involved in flavonoid metabolism and regulators of seed coat development. tt mutants have abnormally high seed coat permeability, resulting in lower seed viability and dormancy. However, the biochemical basis of this high permeability is not fully understood. We show that the cuticles of developing tt mutant integuments have profound structural defects, which are associated with enhanced cuticle permeability. Genetic analysis indicates that a functional proanthocyanidin (PA) synthesis pathway is required to limit cuticle permeability, and our results suggest that PAs could be intrinsic components of the cuticle. Together, these results show that the formation of a maternal cuticle is an intrinsic part of the normal integumental differentiation program leading to testa formation and is essential for the seed9s physiological properties.