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

ABSTRACT Temperatures above the optimum growth temperature affect seed development; accelerating the embryo development and producing seeds with ruptured seed coats. However, the underlying mechanism of this effect remains unclear. To investigate temperature-induced seed coat rupture, we used a combination of detailed phenotyping, transcriptomics, histology, immunolabelling, cell wall profiling and seed coat mechanics to analyse oilseed rape seeds. Our data suggest that high temperatures accelerate embryo growth, resulting in the formation of larger embryos but not larger seeds. The formation of large embryos increases the mechanical stress exerted on the seed coat cells by the embryo, reducing their thickness. Prolonged exposure to high temperatures during seed development causes the seed coat to mature prematurely, resulting in the accumulation of demethylesterified pectin and making the cell wall more rigid. This inhibits cell growth and limits the expansion of the seed. The consequences of these events result in tension building up in the seed coat cells. These cells eventually undergo seed coat rupture, affecting the quality of the seed. Our work on seed maturation and the mechanism of heat-induced seed coat rupture provides valuable insights for future research into generating thermotolerant Brassica napus , crucial in the context of changing climates. HIGHLIGHTS Growth of Brassica napus under long-term high temperatures accelerated the embryo growth and led to half of the seeds undergoing seed coat rupture phenotype. Pathways linked to cell wall modification were found to be significantly misregulated at high temperatures. The stiffening of the seed coat correlated with increased pectin demethylesterification. The faster-growing embryo imparted increased tension to the developing seed coat cells, reducing the thickness of each individual layer. While the seed coat was stiffening, it was unable to restrict the embryo growth, resulting in its rupture.