大麦钩芒突变体的遗传解析

Genetic Dissection of Hooded Awn Mutation in Cultivated Barley(Hordeum vulgare L.)

大麦(Hordeum vulgare L.)的芒是其穗部小花的外稃上端延伸出的针状特化结构,内部有绿色组织细胞和维管组织。芒在大麦的防御、光合作用、籽粒自然脱落后在土壤中的固着和萌发出土等方面均具有重要作用。在禾谷类作物中,大麦是少数仍保留着芒结构的栽培作物,在自然群体中其形态变异丰富。研究大麦芒形态的遗传调控与变异分布,具有重要的理论与应用价值。本研究鉴定了1个大麦的钩芒突变体M7966,通过分离群体遗传分析证实该突变由单个显性遗传位点控制;随后利用遗传群体的分离单株混池测序分析,定位和克隆了引起钩芒表型的目标基因HvKNOX3。在突变体中,该基因第4内含子中的一处305 bp序列原位重复与钩芒突变表型共分离;HvKNOX3为homeobox类转录因子,在发育早期1~1.5 cm长的幼穗及播种后35 d的穗轴中特异性表达,在大麦泛基因组包含的20个品种间保守性高,仅在其外显子区域发现少数核苷酸序列变异,其余序列变异均位于非编码区域。通过设计共显性分子标记对我国不同地区来源的238份栽培大麦地方品种进行了基因型鉴定,结果发现该305 bp突变在西藏地方品种中具有较高的分布比例,为钩芒突变起源于喜马拉雅地区的理论假设提供了证据。

Awn is a specialized extension at the tip of lemma or glume of floret in cereal species,consisting of chlorenchyma cells and vascular bundles which support photosynthesis and nutrients transport,respectively.The awn plays important roles in plant defense,photosynthesis and grain filling,as well as facilitate the threshed grains embedding in soil and the geminated seedlings come up.Cultivated barley(Hordeum vulgare L.)has awn remained post domestication,and various morphological diversifications of the awns have been observed within natural population.Studies on genetical regulation and distribution of the barley awn variants have both theoretical and practical significance.In this study,a barley mutant with hooded awn was identified and genetically attributes to a single dominant mutation.By taking use of bulked-segregants-analysis(BSA)the mutation was mapped towards the end of short arm of the barley chromosome 4H,where the barley gene HvKNOX3 resides in the interval.A local duplication of 305 bp fragments in the fourth intron of HvKNOX3 was found to co-segregate with the hooded phenotype.HvKNOX3,which encodes a homeobox protein with function in transcriptional regulation,expressed specifically in young spikelets 1~1.5 cm long at early development and the rachis of 35 days after planting.By analyzing the sequence diversity of the HvKNOX3 among 20 representative landraces/cultivars of the barley pan-genome,the coding sequences were highly conserved while the exons or untranslated regions were detected with rich amount of variations,others are located in non-coding regions.With a co-dominant marker that captures the 305 bp fragmental duplication in genotyping of 238 Chinese barley landraces,a significant high ratio of the hooded genotype was observed amongst germplasms that collected from Tibet,providing evidence for the presumption that the hooded awn variant was originated from Himalayan area.