Mitochondrial small heat shock protein mediates seed germination via thermal sensing

Seed germination is an energy demanding process that requires functional mitochondria upon imbibition. However, how mitochondria fine tune seed germination, especially in response to the dynamics of environmental temperature, remains largely unknown at the molecular level. Here, we report a mitochondrial matrix-localized heat shock protein GhHSP24.7, that regulates seed germination in a temperature-dependent manner. Suppression of GhHSP24.7 renders the seed insensitive to temperature changes and delays germination. We show that GhHSP24.7 competes with GhCCMH to bind to the maturation subunit protein GhCcmF(c) to form cytochrome C/C(1) (CytC/C(1)) in the mitochondrial electron transport chain. GhHSP24.7 modulates CytC/C(1) production to induce reactive oxygen species (ROS) generation, which consequently accelerates endosperm rupture and promotes seed germination. Overexpression of GhHSP24.7’s homologous genes can accelerate seed germination in Arabidopsis and tomato, indicating its conserved function across plant species. Therefore, HSP24.7 is a critical factor that positively controls seed germination via temperature-dependent ROS generation.