| The strength of rice stem is an important agronomic trait, which has a close relationship with resist lodging of plants. Researchers have shown that the main cause of rice lodging is insufficient mechanical strength of stem. The main components of cell wall that act as the plant skeleton are cellulose, hemicellulose and lignin contents, which have a close relationship with plant mechanical strength.The brittle culm mutant can be a good material to study the mechanism of stem strength and lodging resistance since the cell wall components such as cellulose, hemicelluloses and lignin have changed leading to decrease of stem strength. Meanwhile, due to its unique components, it is expected to become a new type fodder and its raw material will be used to make fuel. At present, many brittle mutants have been found in rice, and related brittle culm genes such as BC1-8, BC10-12, BC14-15, the majority of which were involved in the synthesis of the cellulose that had been fine mapped and cloned. Therefore, further study on molecular mechanism of rice brittle culm mutant help to reveal the molecular mechanism of plant mechanical strength changes, and it would be theoretically and practically significance in rice breeding. A brittle mutant named as be 16(brittle culm 16) was isolated from Nipponbare through EMS (Ethyl Methane Sulphonate) treatment, and a genetic analysis and fine mapping were carried out in this study. The main results were as follows:1. From seedling stage, the brittleness of stem and leaves could be observed in mutant be 16. The plant height and main root length of be 16 were lower than those of wild type. In addition, the mutant also showed shorter panicle, reduced grains per panicle and late maturing.2. The components analysis of stem cell wall showed that the cellulose content in be 16 mutant was sharply decreased by 36.9%, while hemicellulose content was evidently increased by 23.6%, and no significant difference was found in the lignin content between be 16 mutant and wild type.3. Results of the inverted fluorescence microscope showed that the cell shape and arrangement of parenchyma cells in be 16 mutant became irregular and disordered, and the sclerenchyma cell walls under the epidermis layer were thinner than those of wild type. Under the SEM, the parenchyma cell walls and the secondary cell walls of sclerenchyma cells in be 16 mutant under the epidermis layer were thinner than those of wild type.4. The results of genetic analysis indicated that there were 120 wild type plants and 38 brittle culm plants in the F2 population crossed by be 16 mutant and Nipponbare cultivar. The segregation ratio of the wild type and bc16 mutation was 3:1 (χ2= 0.08<χ20.05= 3.84), which means the bc16 mutation was controlled by a single recessive nuclear gene.5. BC16 gene was primarily mapped between Indel markers 2-B and 2-E on the long arm of chromosome 2 by map-based cloning, and then fine mapped in 66.6-kb region between Indel markers 2-F and 2-H with 7 candidate genes.Among these genes, Os02g0738900 was considered to be the most likely candidate gene of be 16 bccause it was involved in the synthesis of the cellulose at the secondary cell wall. DNA sequencing results showed that bc16 and bc3 were coming from different mutation methods.There was a T to A substitution at the very end of the 13th intron of Os02g0738900 which was at the 5113th base location from initiation codon by sequencing, which led an splicing forward mutation in the process of transcription, and six nucleotides were cut into mRNA as a result, which finally cause the stop of translation. Additionally, in the mutant, there were significant decrease in the expression of bc16 gene in roots, culms and leaves by real-time PCR method.. bc16 may influence rice stem brittleness through the regulation of the synthesis of sclerenchyma secondary cells wall and parenchyma primary cells wall. |
PDF Full Text Request