玉米籽粒突变体smk7的表型分析和基因定位

利用甲基磺酸乙酯(EMS)对玉米自交系B73进行诱变,获得一个可以稳定遗传的小籽粒突变体smk7(small kernel 7)。smk7成熟籽粒表现为体积变小,胚和胚乳发育缺陷,百粒重显著降低。突变籽粒发芽率仅为10%,且幼苗黄化不能生长成正常植株。成熟smk7胚乳中淀粉、蛋白、油分含量与野生型籽粒相比无显著差异,但突变体胚乳淀粉粒体积明显变小且形状不规则。smk7突变籽粒在授粉后12 d即可观察到明显的小籽粒和空瘪表型,石蜡切片显微观察显示突变籽粒的胚和胚乳发育迟缓,胚乳基部转移层细胞(BETL)相对于野生型细胞壁向内生长减少,发育受阻。用杂合植株(+/smk7)与多个自交系分别杂交,构建不同背景的F2分离群体,遗传分析结果表明该性状受单隐性核基因控制。利用靶向测序基因型分型(genotyping by target sequencing,GBTS)技术将基因初定位于2号染色体短臂,进一步精细定位发现该基因位于RM1433917和RM1535316两个标记之间约120 kb的物理范围内,共有8个蛋白编码基因。本研究为进一步克隆和解析SMK7基因调控玉米籽粒发育的分子机制奠定了基础。

Phenotype analysis and gene mapping of small kernel 7(smk7)mutant in maize

In this study,a stable small kernel mutant,named small kernel 7(smk7),was isolated from ethylmethane sulfonate(EMS)mutagenesis of maize inbred line B73.Compared with wild type,the smk7 mutants showed smaller kernel size,defective embryo and endosperm development and a significant decrease in 100-kernel weight.The smk7 kernels showed a low level of germination rate at 10%and cannot grow into normal plants.No significant changes were detected in protein,starch and oil content between mature wild type and smk7 kernels,but the starch grains became significantly smaller and irregular in smk7 kernels compared with wild type.The smk7 kernels could be clearly distinguished from the wild type as early as 12 days after pollination(DAP),on the basis of their smaller and emptier phenotype.Microscopic inspection of the paraffin sections revealed that the development of embryo and endosperm were delayed,and the cell wall in growth in basal endosperm transfer layers(BETL)were arrested in smk7 compared with wild type.The F2 populations with multiple backgrounds were constructed by crossing heterozygous plants(+/smk7)with several other inbred lines.Genetic analysis showed that the mutant phenotype was controlled by a single recessive gene.Based on genotyping by target sequencing(GBTS)strategy,the SMK7 was initially mapped on the short arm of chromosome 2.The fine mapping results suggested that SMK7 was located between markers RM1433917 and RM1535316,with a physical distance of 120 kb.There were eight protein-coding genes in this region.This study laid a foundation for further genes cloning and research of the SMK7 function in regulating maize kernel development.