Garlic In The Phytochelatin Synthase Gene Cloning And Functional Analysis

Heavy metals have become one of the most serious environmental pollution problems worldwide. Traditional methods to remove the heavy metals from environments are very expensive and inconvenient. Phytoremediation is a new cheap and effective way that depends plants to clean the environmental pollution. Phytochelatins (PCs) are a type of polypeptide in plant to bind heavy metals. They have been identified in a wide variety of plant species and in some microorganisms. PCs are synthesized from GSH by the catalysis of phytochelatin synthase. So revealing the molecular base of the phytochelatins synthase is very important to understand the mechanism of heavy metal resistance in plants. Until now, the research about phytochelatins synthase genes only focuses on two heavy metal sensitive plant: Arabidopsis thaliana and Triticum aestivum. Many problems about the genes' structures and functions of transcript products are still unclear. Allium Sativum L. (garlic) is a kind of plant which can tolerate much heavy metal stress. In this study, we used this plant and make some research below:1. The physiological performance of garlic under heavy metal stress was determined and we get a conclusion that garlic is one of heavy metal tolerance plants.2. A new phytochelatin synthase cDNA from Allium Sativum L. (AsPCS) was cloned. This cDNA sequence with a full length of 1868 bp contains an open reading frame (ORF) of 506 amino acids and encodes a protein with 55.8 kDa molecular weight. The predicted polypeptide shows high homology with PC synthase from twelve other species;3. The AsPCS-expression yeast cells can tolerate more cadmium and arsenite stress. It suggests that as a key enzyme, the transcript product of AsPCS plays an important role in different heavy metals tolerance.4. The results of RT-PCR showed that the expression of AsPCS was enhanced by Cd2+ in both roots and shoots in garlic. It means that AsPCS was regulated at thetranscriptional level. Moreover, comparing the expression of AsPCS in the roots and shoots, we found that the roots display a much higher expression level than the shoots;5. The results of in situ hybridization demonstrated that AsPCS was found to be expressed in the apical meristem, epidermis, and vascular cylinder of roots. In addition, the expression quality of this gene in epidermis was increased under Cd2+ stress.