粳稻超亲变异系籽粒谷氨酰胺合成酶基因表达特性及序列变异分析

Expression Characteristics and Sequence Variation Analysis of Glutamine Synthetase Gene in Grain of japonica Rice with Transgressive Variation

选用籽粒蛋白质含量有显著差异的亲本和杂种后代超亲变异系,比较分析灌浆过程中籽粒蛋白质积累特性、谷氨酰胺合成酶（GS）活性变化、GS基因mRNA表达量变化和基因碱基序列.结果表明,杂交后代通过籽粒蛋白质含量的连续定向选可获得超亲变异系,籽粒蛋白质积累量与基因型紧密相关;灌浆过程中籽粒GS活性呈单峰曲线变化,籽粒蛋白质含量与籽粒GS活性密切相关,而且籽粒GS活性也能产生超亲变异;在灌浆过程中籽粒蛋白质含量不同的亲本及超亲变异系籽粒GS1.3 和GS2 基因的mRNA表达量变化趋势基本一致,即随灌浆进程mRNA表达量逐渐增加,到抽穗后15-20d表达量最高,随后逐渐下降,呈单峰曲线变化;GS1.3 和GS2 基因mRNA表达量与籽粒蛋白质含量关系密切,GS基因mRNA表达量高的基因型籽粒蛋白质含量也高,而且超亲表达;尽管不同品种GS1.3 和GS2 基因碱基序列保守性很高,但不同品种水稻GS1.3 和GS2 基因的碱基序列和蛋白质氨基酸序列并不完全一致,存在着个别碱基不同的基因多态性,品种间有性杂交后代在基因分离和稳定过程中通过碱基的替换仍然能发生碱基的随机性变化及三联体密码和氨基酸的变化.

The transgressive variants derived from rice varieties with significant difference in grain protein content were used to investigate the expression level and structure of glutamine synthetase gene(GS),activity of glutamine synthetase and protein accumulation characteristics during grain filling.The results showed that transgressive variants could be obtained through successive directive selection of grain protein content,because the grain protein content was closely related to corresponding genotype.During grain filling,the activity of glutamine synthetase followed a single-peak curve,highly correlated with grain protein content and significantly differed between parents and progenies.GS1.3 and GS2 genes,in transgressive variants and their parents with different protein content,exhibited similar transcription trend during grain filling,that is,the transcription level increased 15-20 days before heading and then decreased gradually.Moreover,the grain protein content was closely related to GS1.3 and GS2 expression levels.The varieties with higher GS transcription level showed higher protein content compared with their parents.In addition,although GS1.3 and GS2 gene sequences showed high conservation,the gene sequence and protein sequence of GS1.3 and GS2 were not completely identical in different varieties,and there are some single nuclear polymorphisms.Random base variation as well as changes in codon and amino acids might occur because inter-variety sexual hybridization causes base substitution during segregation and stability.