Genetic analyzes of seed storage protein gene expression in response to environmental stimuli

- conglycin是大豆主要的种子贮藏蛋白之一，主要由α、α′和β三个亚基组成。其中，β亚基是独特的，因为它的表达在硫酸盐缺乏时增强，在蛋氨酸存在时被抑制。构建了携带β -葡萄糖醛酸酶（GUS）基因与β亚基基因启动子融合的转基因拟南芥SNTbeta3。拟南芥突变体mto1-1在营养生长期的莲座叶片中积累的可溶性蛋氨酸浓度高出10- 40倍。然而，一旦突变植株开始开花，莲座叶片中可溶性蛋氨酸的浓度就会降低，突变植株在未成熟果实和顶端区域积累可溶性蛋氨酸。吸胀后40天，突变体植株在这些吸收器官中积累的可溶性蛋氨酸浓度增加了约5倍。构建了mto1-1突变与转基因均纯合子的拟南芥系（SNTbeta3mto）。SNTbeta3mto植株种子中GUS活性为SNTbeta3种子的1/40。将SNTbeta3与mto1-1突变体植株进行反向杂交，并在F1种子中测定GUS活性。结果表明，以mto1-1突变株为母本时，F1种子的GUS活性受到抑制，而以野生型代替mto1-1突变株的反交与对照比较，GUS活性无明显差异。这些结果表明，可溶性蛋氨酸从母体植物转运调节种子中β亚基启动子的活性。

beta-Conglycinin, one of the major seed storage protein of soybean, consists mainly of three subunits, namelyalpha, alpha' and beta.Among these, the beta subunit is unique because its expression is enhanced under sulfate deficiency and repressed in the presence of methionine.Transgenic Arabidopsis thaliana, SNTbeta3, which carries the beta-glucuronidase (GUS) gene fused to the promoter of the betasubunit gene was constructed.An A.thaliana mutant, mto1-1, accumulates 10- to 40-fold higher concentration of soluble methionine in rosette leaves during the vegetative growth period.However, once the mutant plants started to flower, the concentration of soluble methionine in rosette leaves become low and the mutant plants accumulate soluble methionine in immature fruits and the apex region.At 40 days after imbibition, the mutant plants accumulated about 5-fold higher concentration of soluble methionine in these sink organs.An A.thaliana line that is homozygous for both the mto1-1 mutation and the transgene was constructed (SNTbeta3mto).GUS activity in seeds of SNTbeta3mto plants was 1/40 of that of SNTbeta3 seeds.Reciprocal crosses were made between SNTbeta3 and the mto1-1 mutant plants and the GUS activity was measured in the F1 seeds.The results indicated when the mto1-1 mutant plants were the mother, GUS activity in F1 seeds was repressed while there was no apparent difference in the GUS activity in the reverse cross as compared to the control cross in which wildtype plants were used in place of the mto1-1 mutant plants.These results suggest that soluble methionine translocated from the mother plants regulates the beta subunit promoter activity in seeds.