Molecular Genetic Basis Of The S1-mediated Interspecific Hybrid Sterility In Rice

Rice is one of the main crops in the world.Cultivated rice was divided into two species,Asian cultivated rice and African cultivated rice.Hybrids between two cultivated rice species show strong hybrid vigor,but suffer from serious hybrid sterility（HS）which severely limits the utilization of heterosis in rice.The S1 locus is an important interspecific HS locus that causes male and female gamete abortion between Asia rice and Africa rice.Given that the S1 locus which requires at least two key genes,S1TPR and S1A6（SSP）is a complex gene locus,but the molecular mechanism resulting in S1-HS is unclear.Therefore,I explored the molecular mechanism by genetic interaction and molecular interaction in this study.The main results of this study are as follows:1.To investigate the role of S1TPR and S1A6 in S1-HS,I created a functional complementary vector carrying S1TPR-A6,then transformed it into RP-s of Asia rice parent and obtained functional complementary transformants S1TPR-A6^t.The pollen and spikelet fertilities of the transformants showed fully fertile,indicating that other factors may be required for HS.2.To find out the other unknown key factors,I created functional complementary vectors carrying S1A2～S1A5,transformed them into RP-s and produced functional complementary transformants S1A2^t～S1A5^t.The results showed that the pollen and spikelet fertilities of these transformants were fully fertile,meaning that only S1A2～S1A5 can not cause HS,respectively.3.S1A2^t～S1A5^t were crossed with S1TPR-A6^t to polymerize these genes in RP-s.The results showed that the semi-sterile pollen and spikelet were observed in the F₁（S1A4^t-/S1TPR-A6^t-）plants of S1A4^t×S1TPR-A6^t,and the pollen and spikelet fertilities of the other crosses were full fertility.These results strongly indicated that S1A4 is also involved in S1-HS and the three genes,S1A4,S1A6 and S1TPR,lead to gamete abortion in the F₁ plants.4.To further illuminate the genetic relationship among S1TPR,S1A4 and S1A6,I constructed a functional complementary vector harboring S1A4-A6,then transformed it into RP-s and obtained functional complementary transformants S1A4-A6^t.The spikelet and pollen fertilities of F₁（S1A4-A6^t-/S1TPR^t-）plant derived from S1A4-A6^t crossing S1TPR^tshowed semi-sterility,confirming that S1A4,S1A6 and S1TPR are sufficient and necessary for S1-HS.5.To obtain the flanking sequences of the tranformants,I identified the T-DNA insertion sites of S1TPR-A6^t,S1A4^t and S1A4-A6^t through TAIL-PCR and analyzed the segregation ratio of T-DNA in different hybrid F₂ populations.The results showed that the segregation ratio of S1A4^t and S1A4-A6^t fitted normal Mendelian ratio,but the segregation ratio of S1TPR^t and S1TPR-A6^t had strong segregation distortion,suggesting that S1A4,S1A6 and S1TPR form a killer system in the sporophyte,while S1TPR can protect gametes.6.The subcellular localization analysis showed that S1TPR,S1A4,and S1A6 are localized in the nucleus by fusing fluorescent proteins.7.Bi FC and Pull-down assays were used to explore the relationship among S1TPR,S1A4,and S1A6.The results showed that S1TPR-S1A4-S1A6 is a tripartite complex in vivo and S1A4 interacts with S1TPR and S1A6,respectively.In this study,I illuminate genetic interaction and molecular interaction among S1A4,S1TPR and S1A6 which are the key genes of S1-HS,and propose a work model of S1-HS.The results provide a solid foundation for studying the molecular mechanism of S1-HS in future,and give a direction for creating hybrid-compatible materials.