| Plant cell walls are the most abundant renewable resources on the earth. However, humans currently utilize only 2% of the plant cell wall-based biomass. Rice is one of the major food crops across the world and a model species for the functional genomic characterization of monocotyledonous plants. Rice straw is abundant biomass and its mechanical strength is an important agronomy trait which mainly determined by the property of cell wall. Understanding of biosynthesis and regulation of cell wall is thus significantly important. Characterization of eight brittle culm mutant (bc) genes in previous studies is helpful towards the mechanisms of cell wall biosynthesis and modification.This study reported a new be mutant C8 isolated by screening Nipponbare (NPB) T-DNA insertion mutant library. The Culm of C8 mutant is brittle, while the leaf is normal and other agronomic traits remain unchanged. C8 was preliminary mapped in an interval of RM5647-RM22942 on chromosome 8 that indicates C8 is a new be gene that has never reported. The main results are as follows:1. Agronomic traits observation and mechanical testC8 and NPB are only different in the culm breaking force and the culm tension, the traits associated with brittle culm. However, there are no difference in lodging index, the diameter of culm and the thickness, and the agronomic traits including plant height, the tiller number, and the biomass, only the spike mass reduce a little. No obvious difference in structure was observed between C8 and NPB by Calcofluor white staining, while phloroglucinol staining illustrated that the cell wall of sclerenchyma of C8 was a little thicker than that of NPB, and the shape of cells was abnormal and loosing. As C8 stained deeply, it showed that the lignin in C8 was increased.2. Analysis of cell wall composition and structure.Compared with NPB, the cellulose content of C8 decreased little, and the lignin content increased slightly, while the hemicellulose increased 31.9%, suggesting that the C8 gene may associate with hemicellulose synthesis. It is further confirmed by monosaccharide composition analysis by GC-MS that rhamnose, arabinose, xylose, mannose, galactose are all increased in hemicelluloses of C8. The monolignols analysis by HPLC indicated that the content of guaiacyl (G) units was increased largely, syringyl (S) unit was decreased a little, and p-hydroxyphenyl (H) unit was not much changed.3. F2 segregation population and genetic analysisThe F2 segregating populations derived from the cross between C8 and MH63 and were planted in two locations (Wuhan and Ezhou). In Wuhan, the population BP13, A total of 2056 F2 mutant plants, and 35 were brittle culm. In Ezhou the population BB15 and BB17, a total of 314 F2 mutant plants of BB15, and 65 were brittle culm.770 F2 mutant plants of BB17, and 147 brittle culm, BP13 and BB15 are consistent with Mendelian segregation ratio, but BB17 was a little not. BB17 was selected as mapping population.4. Preliminary mapping of C8Out of total 200 SSRs distributed on chromosomes3-9, there were 136 markers showing polymorphism between C8 (NPB background) and MH63, and the polymorphism rate was 68%. To map the C8, two pools, one was brittle and the other was normal, were generated and BSA method was used. The markers RM408, RM6356 and RM1376 on chromosome 8 were polymorphic between two pools, and the association of there markers with C8 was verified using F2 population BB17, Then, the C8 is further mapped to a 101kb region framed by two markers RM5647 and RM22932.5. The candidate genes of C8A total of 16 predicated genes were found between markers RM5647 and RM22932 using RICE GENOME AMMOT-ATION PROJECT (http://rice.plantbiologymsu.edu/). Among them, LOC_Os08g05510.1 and LOC_Os08g05520.1 belong to MYB transcription factor family, and LOC_Os08g05560.1 contain zinc finger. These genes need further investigation. |
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