| Rice (Oiyza sativa L.), the staple food for almost50%of the world’s population, is researched more and more in-depth and extensively. It is rice researchers’dreams to cultivate such as high-yield, insect-resistant, high-quality, well adaptability and so on in rice. Research on the rice growth period, especially the heading stage (flowering stage), is one of hot spots of rice study. Heading early or late and size of panicles is directly to impact on rice yield and quality. Most of research of genetic characteristics and molecular mechanisms of rice heading date are conducted compared with the similar researched results of Arabidopsis. However, many regulation ways and actions of heading date are found in rice show that it is completely different compared with Arabidopsis, revealing that the rice has a more complex and higher control system. While, so far the research fruits on rice flowering are just the tip of the iceberg. To clarify the molecular regulation mechanisms of rice heading date, not only contributes to enhance human knowledge, but also is an important significance in the actual production and breeding.The rice heading date related mutant was obtained from a M2generation which was from a japonica Zhejing22via radiation of60Co-γ-ray. The heading date of the mutant was delayed for almost20days than the wild type and the mutant was temporarily named as hd(t)(heading date). In this study, we have observed the traits, detected the photonasty, analyzed the genetic characteristic and mapped the gene of the hd(t) mutant. The main results are as following: 1. The observation of hd(t) mutant traits:The heading date of the mutant was delayed for almost20days than the wild type. The leaf color and the plant height of the mutant was greener and higher comparing with wild type plant both in heading stage and grain-filling stage. And the flag leaf of main stem of mutant was longer than the wild type’s. Besides, the rice panicle of mutant was a little larger than the wild type’s. The width and length of mutant seed grains were longer and shorter than the wild type’s. In addition, no significant difference was observed in seedling height between the mutant plant and the wild type plant at one-leaf stage, but mutant roots lengths were about twice as long as the wild type’s at this time.2. The detection of hd(t) mutant photonasty:In rice growing season, an artificial short day (SD) conditions (10h light/14h dark) treatment was carried out for the detection of mutant photonasty. The results suggested that the trait of hd(t) mutant might not be caused by short photoperiod treatment.3. Genetic analysis of hd(t) mutant:The mutant was crossed with Zhejing22(wild type) so as to analyze the late heading date trait genetically. In the F1s, all the hybrids displayed same as the WT heading date, suggesting that the late heading date trait was controlled by a recessive gene. In the F2segregation population, the number of individuals was found to be similar to the mutant and the number of individuals was found to be similar to the wild type were123and335, fitting the1:3ratios. The result indicated that mutant trait was fitted by the Mendel’s Laws and was controlled by a single nuclear-encoded recessive gene.4. Fine mapping of Hd(t):A map-based cloning approach was employed for fine mapping the Hd(t) gene. A total of479individuals with typical mutant phenotype in the F2segregation population of hd(t) mutant/Zhenshan97were selected for the gene Hd(t) mapping. The Hd(t) gene was finally mapped in an approximate53kb region between the In/Del markers of10-61W and10-66W on chromosome10. According to the genome sequence of Nipponbare, the target region contained13annotated genes. In this region, we found a heading date related gene Ehdl (early heading date1)(msu: LOC_Osl0g32600). According to the sequencing results of LOC_Os10g32600 genomic sequence and promoter region of LOC_Os10g32600, there was no any base pair mutation in LOC_Os10g32600promoter region while there was a T base-pair deletion at60bp site after start coding areas and early stopped coding at67bp site in hd(t) mutant compared with wild type. This mutation might be the cause that leaded to delay heading date in hd(t) mutant. |
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