Scientists discovered mutation in single rice gene cancels interspecific hybrid sterility

A new study to modify food production.

Rice Farming, Green, Nature
Asian species (Oryza sativa, top), African species (O. glaberrima, bottom), and their hybrid (middle). The hybrid has husks but does not yield seeds.

Scientists jointly from Hokkaido University, Japan International Research Center for Agricultural Sciences (JIRCAS) and Kyoto University successfully employed mutagenesis to recognize the gene that causes hybrid sterility in rice, which is a chief reproductive interrupt between species.

This study is anticipated to assist explicate the genetic basis of interspecific hybrid sterility, which is prominent not only for tracing the advanced biology of speciation but also for modifying crops for food production.

There are only two cultured rice species: an Asian one (Oryza sativa) and an African one (O. glaberrima). The African species is tolerant to several abiotic and biotic stresses such as high temperature, producing a valuable source of genes that could be useful in rice production. However, the interspecific reproductive barrier stands in the way of utilizing the African species in breeding episodes with the Asian species. Plants received from hybridizing the two species yield almost no seeds when they are cultivated. This is known as hybrid sterility.

Later to find the cause of this infertility, Assistant Professor Yohei Koide and Associate Professor Akira Kanazawa of Hokkaido University along with their collaborators’ Senior Researcher Yoshimichi Fukuta from JIRCAS and Professor Yutaka Okumoto from Kyoto University scrutinize on the S1 gene locus, which is perceived to be part in hybrid sterility.

The team produced a number of hybrid seeds heterozygous for the S1 locus, which were then subjected to heavy-ion beam irradiation to induce mutations. The irradiation experiments were conducted at RIKEN.

Further while screening for mutants, they discovered plants that produced seeds, thus fertile, despite being heterozygous for the S1 locus. Succeeding gene analysis of the S1locus discovered a deletion in the peptidase-coding gene called SSP. When the team brought the intact SSP into the Asian species by transformation experiments and crossed the transformant with the mutant, it regained hybrid sterility, showing SSP is causative.

Interestingly, the transformation alone did not show sterility, suggesting that SSP is indispensable but not enough for hybrid sterility.

Researchers then invented the evolutionary pathways of SSP and discovered that the gene is existing mere in the African species and some other wild species, not in the Asian one. This unfolds the gene was acquired or lost in certain evolutionary pathways and maintained interspecific boundaries.

Yohei Koide said, “Our study shows the intraspecific reproductive barrier can be overcome by a disruption of a single gene. Further research could help improve breeding programs and enhance rice yields to address food shortages in growing populations.”