Two Petroleum-Induced Small Heat Shock Proteins of Mirabilis jalapa Confer Tunicamycin Tolerance in Transgenic Saccharomyces cerevisiae

The phytoremediation technology is widely used due to its beautiful appearance and no secondary pollution. The mechanism of how the plants cope with the abiotic stresses imposed by polyaromatic hydrocarbon and other organic pollutants is not fully explored. Our previous study showed that the expression of MjHSP18.2 (small heat shock protein 18.2) and MjHSP17.7 (small heat shock protein 17.7) was remarkably upregulated in Mirabilis jalapa L. under petroleum stress through the predifferential proteome analysis. To improve our understanding of small heat shock proteins (sHSPs), we have characterized MjHSP18.2 and MjHSP17.7 from M. jalapa. Sequence alignments and phylogenetic analysis reveal these to be a cytosolic class I sHSPs. MjHSP18.2 and MjHSP17.7 expression was induced by petroleum stress in M. jalapa. Recombinants MjHSP18.2 and MjHSP17.7 were overexpressed in yeast Saccharomyces cerevisiae to study its possible function under stress conditions. The recombinant yeast cells that accumulated MjHSP18.2 and MjHSP17.7 conferred tolerance to tunicamycin compared with control cultures. Under tunicamycin-induced endoplasmic reticulum (ER) stress conditions, MjHSP18.2 and MjHSP17.7 transgenic yeast cells were found to depress the expression of ER molecular chaperones, increase cell viability, decrease cell apoptosis, and increase superoxide dismutase activities compared with control cultures. These results suggest that MjHSP18.2 and MjHSP17.7 could alleviate the ER stress caused by tunicamycin and promote cell survival in yeast cells.