A seed coat-specific β-ketoacyl-CoA synthase, KCS12, is critical for preserving seed physical dormancy ($) (Plant Physiol.)

Physical dormancy is a dormancy class caused by a water-impermeable cell layer that prevents seed water uptake. Despite being present in several families, its molecular basis has seldom been addressed. Here, Chai and colleagues identify a β-ketoacyl-CoA synthase (KCS) –one of the enzymes that participate in very long chain fatty acid (VLCFA) biosynthesis– involved in the acquisition of physical dormancy in Medicago truncatula. Previous studies reported that M. truncatula knox4 mutants lack physical dormancy and presented less content of VLCFAs. Moreover, these mutants also exhibited a downregulation in KCS12, a KCS whose expression was specific to the seed coat. Further mutant analysis showed that kcs12 seeds were not physically dormant and could absorb water just like scarified wild-type seeds. In line with these, kcs12 seeds had a thinner cuticle with altered VLCFAs composition. Notably, these seeds showed a reduction in the content of 24C VLCFAs, suggesting that KCS12 is responsible for their synthesis and that they are required to achieve physical dormancy. Therefore, this research provides exciting insights into the molecular mechanisms underpinning physical dormancy. (Summary by Carlos A. Ordóñez-Parra @caordonezparra) Plant Physiol. 10.1093/plphys/kiab152