Cloning And Functional Analysis Of Rice Pleiotropic QTL,Ghd8

Adaptability of rice is largely affected by its flowering time, which also greatly affects yield rice; spikelets per panicle is a very important yield component and directly determines rice production; rice plant height is associated with its architecture, biomass and lodging properties. Thus, genetic dissection of the yield related agronomic traits, such as plant height, flowering time and number of spikelets per panicle, will provide theoretical guidance to the improvement of rice production. In this study, map-based cloning method was used to fine mapping a rice pleiotropic QTL with major effect, Ghd8, The function of the gene was finally confirmed by complementation test. Ghd8simultaneously affects rice flowering time, plant height and grain number per panicle. After cloning the gene, we tried to elucidate the molecular mechanism of the gene controlling rice flowering and panicle development. Also, we have tested the function of Ghd8in dicotyledonous plant Arabidopsis. The results are as follows:1. Map-based cloning approach had been applied to clone the pleiotropic QTL, Ghd8, which could delay rice flowering for10days, increase plant height for20cm and result in50%more grain per plant under the NIL background. The gene encodes a CCAAT binding protein (CCAAT-binding factor), belonging to heterotrimeric heme activator protein (heterotrimeric heme activator protein, HAP) gene family. Ghd8expressed in various rice tissues and organizations. Especially, strong signals had been detected in leaf and panicle meristem. We had introduced GHD8and yellow fluorescent fusion protein into rice protoplasts, the result showed that Ghd8protein was localized in the nucleus.2. Function of Ghd8is affected by its allele variation. Ghd8allele derived from Nipponbare is the weak allele which only causes10days’delay of rice heading while the strong allele of Ghd8from indica rice variety9311which delays rice heading for20days in near-isogenic lines background.3. GHD8protein localized in the nucleus, but it might not be a transcription factor. Transcriptional activation or transcriptional repression activity could not be detected and in addition, over-expression of Ghd8in a Ghd8functional background does not lead to heading date phenotype variation but suppression of Ghd8could delay rice heading date for2-3days.4. Ghd8inhibits rice flowering under long-day conditions through negatively regulating rice specific flowering regulator Ehdl and rice florigen Hd3a and RFT1. Ghd8can not affect the expression of OsGI, Hdl or OsMADS50.5. Ghd8is allelic with Hd5and in fact they are the same gene. Previously it was reported that Ghd8epististicly interacted with Hdl and our result showed the two genes could not regulate the espression of each other. Meanwhile, GHD8protein could interact with HD1protein.6. Ghd8regulates rice panicle size through acting on rice inflorescence branch development. Ghd8can promote the expression of MOC1gene and increase the number of rice primary branches and secondary branches. Compared with the control, Ghd8transgenic plants also produce more tillers.7. Ghd8is the close homologous to Arabidopsis Hap3b gene. Over-expression of Ghd8in Arabidopsis can cause early flowering under long-day conditions, which is similar to that of Hap3b over-expression in Arabidopsis. The result indicated that the function of Ghd8and Hap3b is conserved.8. Pyrimiding of Ghd7and Ghd8caused extremely late flowering in rice. Cloning of Ghd8not only provides us a better understanding to the molecular mechanism of rice flowering time regulation, plant height and panicle development but also supplies us a good genetic tool for genetic improvement. We hope that we could suitably introduce this Ghd8gene during the genetic improvement of rice yield and adaptation after we fully understand the molecular mechanisms of Ghd8.