Hybrids between the indica and japonica subspecies of rice (Oryza sativa)
are usually sterile, which hinders the use of heterosis in the
inter-subspecific hybrid breeding. The complex locus Sa comprises two
adjacently located genes, SaF and SaM, which interact to cause abortion of
pollen grains carrying the japonica allele in japonica-indica hybrids. In
this study, Yongyao Xie of the South China Agricultural University aims to
restore male fertility in indica-japonica hybrids via silencing of SaF or
SaM.

RNA interference restored male fertility in indica-japonica hybrids with
heterozygous Sa. The team then used CRISPR-Cas9 genome editing to knockout
the SaF and SaM alleles of an indica rice line to create hybrid-compatible
lines. The resultant alleles did not affect pollen viability and other
agricultural traits, but broke down the reproductive barrier in the hybrids.
They also found that some rice lines have natural neutral allele Sa-n, which
was compatible with the typical japonica or indica alleles in hybrids.

This study provides basis for the generation of hybrid-compatible lines by
knocking out the Sa locus or using the natural Sa-n allele to overcome
hybrid male sterility in rice breeding.

[onlinelibrary.wiley.com]