Regulation of Wx gene expression to low amylose in wheat endosperm

小麦胚乳中直链淀粉的合成主要受分子量约为60 kDa的颗粒结合型淀粉合成酶（Wx蛋白）控制。Wx蛋白是位于染色体7A（Wx-Al）、4A（Wx-Bl）和7 D（Wx-Dl）上的一式三份单拷贝同源染色体组处的Wx基因的产物。以“中国春”及其缺体-四体、四体、双端体和缺失株系，以及这些染色体的单染色体代换系为材料，研究了全染色体和染色体臂剂量的变化以及无效等位基因对直链淀粉合成的影响。缺失体4A和携带Wx-Bl基因的染色体片段的缺失使直链淀粉含量降低超过3%。在代换系中发现了合理的一致性。这证实了Wx-B1基因的缺失或该基因被其无效等位基因取代对降低直链淀粉合成具有最显著的后果。去除携带Wx-Al或Wx-Dl基因的染色体使直链淀粉含量降低小于2%。用无效等位基因取代这两个基因也显示出类似的减少。染色体7A，4A和7 D的双剂量没有增加直链淀粉含量，而四体染色体产生更多的各自的Wx蛋白。这表明一定水平的Wx基因活性或Wx蛋白导致最大量的直链淀粉。

Amylose synthesis in wheat endosperm is mainly controlled by the granule-bound starch synthase of about 60kDa or so-called waxy (Wx) protein. The Wx proteins are the product of the Wx genes at a triplicate set of single-copy homoeoloci located on chromosomes 7A (Wx-Al), 4A (Wx-Bl) and 7D (Wx-Dl). Using 'Chinese Spring' and its aneuploid lines including nullisomic-tetrasomics, tetrasomics, ditelosomics and deletion stocks, and single-chromosome substitution lines for these chromosomes, the effects of varying the dosage of whole chromosomes and chromosome arms, as well as the effects of null alleles, upon amylose synthesis were investigated. Nullisomic 4A and deletion of chromosome segments carrying the Wx-Bl gene reduced the amylose content by more than 3%. A reasonable agreement was found in the substitution lines. This confirms that the absence of the Wx-Bl gene or substitution of this gene by its null allele has the most striking consequence on decreasing amylose synthesis. The removal of chromosomes carrying either the Wx-Al or Wx-Dl gene reduces amylose content by less than 2%. A similar reduction was revealed by substitution of these two genes by the null alleles. Double dosages of chromosomes 7A,4A and 7D did not increase amylose content, while the tetrasomic chromosomes produced more of the respective Wx proteins. This suggests that a certain level of the Wx gene activity or the Wx proteins led to a maximum amount of amylose.