Key Laboratory of Forage and Endemic Crop Biotechnology, Ministry of Education, School of Life Sciences, Inner Mongolia University, Hohhot, 010010, PR China.
Key Laboratory of Forage and Endemic Crop Biotechnology, Ministry of Education, School of Life Sciences, Inner Mongolia University, Hohhot, 010010, PR China; State Key Laboratory of Reproductive Regulatory and Breeding of Grassland Livestock, Inner Mongolia University, Hohhot, 010010, PR China; Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, Beijing, 100081, PR China.
J Plant Physiol. 2020 Sep;252:153208. doi: 10.1016/j.jplph.2020.153208. Epub 2020 Jun 10.
Arabidopsis thaliana BRANCHING ENZYME 1 (AtBE1) is a chloroplast-localized embryo-lethal gene previously identified in knockout mutants. AtBE1 is thought to function in carbohydrate metabolism; however, this has not been experimentally demonstrated. Chlorosis is a typical symptom of cesium (Cs) toxicity in plants. The genetic target of Cs toxicity is largely unknown. Here, we isolated a Cs-tolerant and chlorophyll-defective Arabidopsis ethyl methanesulfonate (EMS) mutant, atbe1-5. Mapping by sequencing and genetic complementation confirmed that a single amino acid change (P749S) in a random coil motif of AtBE1 confers the mutant's Cs-tolerant and chlorophyll-defective phenotype. An isothermal titration calorimetry assay determined that the 749th residue is the Cs-binding site and hence likely the target of Cs toxicity. We hypothesized that binding of Cs to the 749th residue of AtBE1 inhibits the enzyme's activity and confers Cs toxicity, which in turn reduces photosynthetic efficiency. In support with this hypothesis, atbe1-5 leaves have a reduced photosynthetic efficiency, and their amylose and amylopectin contents are ∼60 % and ∼1%, respectively, of those in Col-0 ecotype leaves. Leaves of the mutant have a lower sucrose, but higher maltose, concentration than those of Col-0. This study demonstrated that AtBE1 is an essential gene for amylopectin and amylose biosynthesis, as well as the target of Cs toxicity; therefore, it can serve as a genetic locus for engineering plants to extract Cs from contaminated soil while maintaining growth.
拟南芥 BRANCHING ENZYME 1（AtBE1）是一种定位于叶绿体的胚胎致死基因，先前在敲除突变体中被鉴定出来。AtBE1 被认为在碳水化合物代谢中发挥作用；然而，这尚未通过实验证明。缺绿症是植物中铯（Cs）毒性的典型症状。Cs 毒性的遗传靶标在很大程度上是未知的。在这里，我们分离出一个耐 Cs 和叶绿素缺陷的拟南芥乙基甲磺酸（EMS）突变体，atbe1-5。通过测序和遗传互补作图证实，AtBE1 中一个随机卷曲基序中的单个氨基酸变化（P749S）赋予了突变体的耐 Cs 和叶绿素缺陷表型。等温滴定量热法测定表明，第 749 位残基是 Cs 结合位点，因此可能是 Cs 毒性的靶标。我们假设 Cs 与 AtBE1 的第 749 位残基结合抑制了酶的活性并赋予了 Cs 毒性，进而降低了光合作用效率。支持这一假说，atbe1-5 叶片的光合作用效率降低，其直链淀粉和支链淀粉含量分别为 Col-0 生态型叶片的约 60%和 1%。突变体叶片的蔗糖浓度较低，但麦芽糖浓度较高，比 Col-0 叶片高。这项研究表明，AtBE1 是支链淀粉和直链淀粉生物合成的必需基因，也是 Cs 毒性的靶标；因此，它可以作为一个遗传基因座，用于工程植物从污染的土壤中提取 Cs，同时保持生长。
