Fig. 1.

S1A4-S1TPR-S1A6 constitutes a killer–protector system. a The structures of the African rice allele S1-g (g) and Asian rice allele S1-s (s). A point (C-to-A) mutation of S1TPR (TPR) results in a premature stop codon in S1TP (TP). African rice-specific sequences are in green. Six putative genes specific to African rice, S1A1–S1A6 (A1–A6), were located in S1-g. Red arrows, CRISPR/Cas9 target sites. b–d The fertility of the transgenic plants of RP-s (the recurrent parent of O. sativa ssp. japonica with ss) and their hybrids carrying different combinations of the transgenes TPR^t (T) and linked A4–A6^t (46). The T₀ plants carrying one (b) or two (c) transgenes were fully fertile (FF, ~95% fertility), as observed in their pollen (top) and spikelets (bottom); however, the co-existence of the three transgenes (all in hemizygous state; ‘–’ denotes absence of the T-DNA/transgene in the chromosome site) induced semi-sterility (SS, 45~55% sterility) of the pollen and spikelets (green spikelets are sterile). d Bars, 50 μm for pollen and 5 cm for panicles. e The segregation of the A4–A6^t and TPR^t transgenes in the T₁ family, and the segregation of the A4–A6^t in F₂ population derived from A4–A6^t (homozygote) × TPR^t (homozygote) fit the 1:2:1 ratio, but the segregation of the TPR^t transgene in this F₂ population was significantly distorted (***P < 0.001 in the Χ² test) from the ratio. f A deduced model for the segregation behavior of the transgenes in the F₂ progeny derived from A4–A6^t × TPR^t. The F₁ male and female gametes containing T are fertile, and those lacking T are generally sterile. The color codes are consistent with the genotype of the individuals in the F₂ population. Black represents homozygous TPR^t; dark orange represents homozygous A4–A6^t; orange represents hemizygous A4–A6^t; light orange represents lacking A4–A6^t. Source data of (e) are provided as a Source Data file