Long-term high temperatures affect seed maturation and seed coat integrity in Brassica napus

O_LITemperatures above the optimum growth temperature affect seed development, producing seeds with ruptured seed coats. This phenotype is associated with accelerated embryo development. However, the molecular mechanism underlying this effect remains unclear. C_LIO_LITo investigate the occurrence of temperature-induced seed coat rupture, we combined detailed phenotyping approaches of oilseed rape seeds with transcriptomics, histology, immunolabelling, hormone and cell wall profiling. C_LIO_LIOur data suggest that high temperatures accelerate embryo growth, resulting in the formation of larger embryos but not larger seeds. The formation of large embryos increased the mechanical pressure exerted by the embryo on the seed coat cells, reducing their thickness. The seed coat began to mature prematurely with the accumulation of demethylesterified pectin, possibly making the cell wall stiffer. Application of abscisic acid, a hormone involved in seed dormancy, did not rescue the seed coat rupture phenotype. Hormonal and transcriptional profiling indicated that the embryo did not enter dormancy. C_LIO_LIProlonged high temperatures during seed development accelerated embryo growth by stimulating cell division, while the seed coat, which depends on cell elongation, could not withstand the tension exerted by the embryo, started seed maturation and eventually ruptured. C_LI