イネにおける温度感受性種間生殖隔離を付与する三者間花粉キラー・プロテクターシステム

Hybrid-sterility-mediated reproductive isolation is pivotal for speciation, yet the underlying molecular mechanisms and its response to the environment remain elusive. Here, we report a temperature-sensitive pollen killer-protector system at a three-gene Sa locus for indica-japonica rice hybrid sterility. Genetic analyses identified SaFL⁺, a strong pollen protector from Sa-i (indica allele), and SaFL^-, a weak japonica allele from Sa-j exclusively functional under high temperatures. Protein interaction, ubiquitination, and degradation assays showed that SaF⁺ and SaM⁺ from Sa-i form a pollen-killer complex to bind and ubiquitinate the reactive oxygen species scavenger COX11 for degradation in mitochondria, causing male sterility of the Sa-j pollen. Protein affinity and competitive binding assays indicated that in the Sa-i pollen, SaFL⁺ binds SaM⁺ to disrupt the killer complex and restore fertility. However, the weak protector SaFL^- can bind SaM⁺ under high temperatures, sparing the Sa-j pollen from sterility. Synteny comparisons and haplotype analyses showed that the Sa locus originated in ancient wild rice and underwent divergence in the Oryza genus during expansion from tropical to temperate environments, which might have driven the latitudinal adaptation and reproductive isolation of rice populations. Thus, Sa represents a temperature-sensitive reproductive-isolation system associated with domestication and environmental adaptation in rice.