水稻籽粒灌浆突变体gef1的鉴定及其基因定位

Identification and gene mapping of a grain-filling mutant gef1 in rice

籽粒灌浆是水稻(Oryza sativa)生长发育过程中极为重要的阶段,涉及复杂的遗传调控网络和环境互作,直接关系到水稻产量和品质的形成.本研究通过甲基磺酸乙酯(EMS)诱变籼稻品种宜香1B,筛选到一个能稳定遗传的籽粒灌浆延长突变体gef1(grain extended filling 1).与野生型相比,该突变体灌浆速率下降,灌浆延长约30 d,且籽粒变大,结实率下降.相关生理指标测定表明,突变体gef1在整个灌浆过程中光合同化物供应正常,但同化物的分配与转化效率较低.对突变体gef1组织细胞学观察发现,穗轴与茎秆部位的大维管束数量减少,表明同化物的运输效率降低是影响灌浆速率的原因之一;颖壳内表皮细胞纵向伸长且数量增多,推测籽粒大小的改变与细胞的数量及形状有关.基因表达分析表明,gef1影响籽粒中糖代谢相关酶的表达;遗传分析表明,该突变表型受单隐性核基因控制,利用图位克隆法将gef1基因定位于水稻第3染色体短臂标记InDel3-1与InDel3-2之间198 kb的范围内,在该区域内尚未有与水稻籽粒灌浆相关基因的报道.

Grain filling is an extremely important process in rice growth and development. This process which involves complex genetic regulatory networks and environmental interaction, is directly related to the formation of rice yield and quality. A stable inherited mutant with grain extended filling（gef1） was identified from an EMS mutagenized population of Yixiang 1B. The investigation of agronomic traits, measurement of physiological and biochemical characteristics, histology observation, gene expression analysis and gene mapping were performed in this study. Compared with the wild type plants, the grain filling rate of gef1 was significantly lower than that of Yixiang 1B, resulting in the grain filling time of gef1 was about 30 days delay. Meanwhile, the 1000-grain weight of gef1 became bigger and seed setting rate decreased by 22%. During the development of caryopsis, we found that the soluble sugar content in wild type showed a single peak curve, and the content maintained at a low level throughout the grain filling stage. However, the soluble sugar content of the gef1 was significantly higher than that of the wild type, and showing a bimodal curve. It revealed that the transportation and distribution of photosynthate, and starch synthesis were inefficiency in gef1. In addition, histocytological analysis showed that the number of big vascular bundles in the same transection parts of rachis, the first top internodes and the second top internodes were all decreased in gef1, and indicated that the transport efficiency of photosynthate was one of the limiting factors in the rate of grain filling. The scanning electron microscope showed that the glume of gef1 had smooth surface and slender cells. Scanning of grain transection showed that gef1 had spherical amyloplasts and arranged loosely, but the wild type had unregular polygon amyloplasts and packed closely. These results suggested that the changes of grain size associated with the cell number and shape of glume, and gef1 had impact on rice quality. Additionally, by analyzing the expression of the glycometabolism-related genes in developing caryopsis, we found that all of them were keeping at a low level in gef1 compared with the wild type. By analyzing the three crosses gef1/Yixiang 1B, gef1/02428 and gef1/Kitaake, we found that the F1 plants of these three crosses were all normal and indicated that the mutant trait was controlled by a recessive gene. The ratio of normal plants to mutant plants in the three F2 populations was 3：1 and indicating that the mutant trait was controlled by a single recessive nuclear gene. gef1 was preliminarily mapped on the short arm of rice chromosome 3, and was narrowed to a 198 kb region between InDel3-1 and InDel3-2. This region has 21 open reading frames and there was no homologous gene had been reported within it, and the further identification work of candidate genes is ongoing.