[Objective]Culm strength, an important agronomic trait, is related to lodging resistance of rice. The research of brittle culm mutants and genes has great significance to demonstrate the regulation of genetic mechanism of culm mechanical strength and breed lodging resistance varieties.[Method]In this study, a brittle culm mutant, named bc1-wu3(brittle culm 1 from Wuyujing 3), was obtained from thejaponicavarietyWuyujing 3 after60Co-γinduced mutagenesis. F2 population derived frombc1-wu3/Kasalath was used to mapping this corresponding gene by position cloning approach.[Result]The mutant was characterized by the brittle leaf, leaf sheath, and culm during the whole growing stage. Compared with the wild type, the panicle length and grain length ofbc1-wu3decreased significantly, and the grain width presented a significant increase. There was a significant decrease in the cellulose content in culm, the number of sclerenchyma cell layers and the thickness of sclerenchyma cell wall, but the contents of xylose, glucose and arabinose increased significantly inbc1-wu3. Genetic analysis showed that the brittle trait inbc1-wu3 was controlled by one single recessive nuclear gene, and the locus was mapped to a 57 kb genomic region on chromosome 3 between molecular markers M12 and Mk18. In the mapped region the cloned brittle culm geneBC1(LOC_Os03g30250) was included, which might be the candidate gene ofbc1-wu3. Sequence analysis revealed that there was a single-base substitution(G-T) in the second exon ofBC1gene inbc1-wu3 mutant, leading to a residue substitution from cysteine to phenylalanine. The data from real-time RT-PCR indicated that there was significant decrease in the expression ofBC1gene in the culm of the mutant.[Conclusion]Based on these results,we speculate that thebc1-wu3 gene is allelic toBC1 gene. These results would deepen our understanding for the function ofBC1and help us to clarify the genetic mechanisms of culm strength.%[目的]茎秆机械强度与植株抗倒伏性直接相关.发掘脆秆突变体,克隆其相关基因有助于了解茎秆机械强度遗传机制,为抗倒伏育种提供理论依据.[方法]在经60Co-γ 诱变的粳稻品种武育粳3号后代群体中获得一个脆秆突变体,命名为bc1-wu3(brittle culm 1 from Wuyujing3),以突变体bc1-wu3为母本,Kasalath为父本构建相应的F2分离群体,采用图位克隆的方法定位相应脆秆基因.[结果]与野生型相比,突变体的叶片、叶鞘、茎秆等组织在全生育期始终表现为脆性,易折断;穗长和粒长显著降低,粒宽显著增加.茎秆细胞细胞壁糖成分测定表明,细胞壁中纤维素含量极显著下降,而木糖、葡萄糖及阿拉伯糖含量则显著增加.茎秆切片观察发现突变体茎秆的厚壁细胞层数减少,厚壁细胞细胞壁极显著变薄.遗传分析表明,bc1-wu3脆性性状受1对隐性核基因控制.采用图位克隆的技术将该基因定位于第3染色体标记MK12与MK18之间,物理距离为57 kb,在此定位区段内包含1个已克隆的脆性基因BC1(LOC_Os03g30250).测序结果表明,突变体bc1-wu3中BC1基因第2外显子内(CDS 659处)有1个碱基的替换(G-T),导致编码氨基酸由半胱氨酸变异为苯丙氨酸.实时荧光定量PCR结果表明,BC1基因在脆秆突变体bc1-wu3茎秆中的表达量显著降低.[结论]据此推断本研究中定位的脆秆基因bc1-wu3为BC1新等位基因.相关结果加深了对BC1基因功能的认识,有助于阐明水稻茎秆强度遗传机制.
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