Type 1 Metallothionein (ZjMT) Is Responsible for Heavy Metal Tolerance in Ziziphus jujuba.

Metallothioneins (MTs) are a family of low molecular weight, cysteine-rich, metal-binding proteins that are able to make cells to uptake heavy metals from the environment. Molecular and functional characterization of this gene family improves understanding of the mechanisms underlying heavy metal tolerance in higher organisms. In this study, a cDNA clone, encoding 74-a.a. metallothionein type 1 protein (ZjMT), was isolated from the cDNA library of Ziziphus jujuba. At the N- and C-terminals of the deduced amino acid sequence of ZjMT, six cysteine residues were arranged in a CXCXXXCXCXXXCXC and CXCXXXCXCXXCXC structure, respectively, indicating that ZjMT is a type 1 MT. Quantitative PCR analysis of plants subjected to cadmium stress showed enhanced expression of ZjMT gene in Z. jujuba within 24 h upon Cd exposure. Escherichia coli cells expressing ZjMT exhibited enhanced metal tolerance and higher accumulation of metal ions compared with control cells. The results indicate that ZjMT contributes to the detoxification of metal ions and provides marked tolerance against metal stresses. Therefore, ZjMT may be a potential candidate for tolerance enhancement in vulnerable plants to heavy metal stress and E. coli cells containing the ZjMT gene may be applied to adsorb heavy metals in polluted wastewater.

Selection of housekeeping genes for gene expression studies on the development of fruit bearing shoots in Chinese jujube (Ziziphus jujube Mill.).

Chinese jujube (Ziziphus jujube Mill.) is important economically for its fruit and also bears attractive medical value. Its flower development concurs with the growth of current fruit bearing shoots (FBSs). However, events involved in current FBSs, including FBS differentiation, flower development, and reliable housekeeping gene are still unknown. In this study, the morphology of FBS development and floral formation were examined and expression profiles of several potential internal control genes was determined. These included genes encoding proteins involved in protein translation (translation elongation factor 1alpha, ZjEF1), protein folding (cyclophilin, ZjCyP) or degradation (ubiquitin extension protein, ZjUBQ), and proteins involved in the structure of the cytoskeleton (beta-actin, ZjACT) or nucleosome (histone3, ZjH3). Our results showed that the floral development in early growing FBSs (less than 20 mm in length) or shoot apices was not complete. Among ZjACT, ZjEF1, ZjCyP, ZjUBQ, and ZjH3, ZjH3 was the most suitable housekeeping gene to evaluate FBS development, based on their expression in early growing FBSs, shoot apices, and different organs. These results will be useful for further molecular mechanism study about FBS development in Chinese jujube.