ABSTRACT Phytoene synthase (PSY) is the rate-limiting enzyme for carotenoid biosynthesis. To date, several studies focused on PSY genes in the context of abiotic stress responses. In this study, two phytoene synthase encoding genes, IbPSY1 and IbPSY2, were identified from a published transcriptome and bioinformatic analysis showed that they shared conserved domains with phytoene synthases from other plants. The IbPSY1 gene was cloned and carefully characterized. Digital gene expression profiling (DGE) showed that the highest transcription level of IbPSY1 was in young leaves, and the lowest level was in stems. In vivo expression levels of IbPSY1 under abiotic stress were observed to be highest in stems at day 11. Over-expression of IbPSY1 in Escherichia coli and yeast cells endowed the cells with better growth under salt and drought stress than the control cells. This study demonstrated that IbPSY1 not only played an important role in vivo, but also in E. coli and yeast to improve tolerance to salinity and drought stress. Thus, IbPSY1 may be aid in the development of transgenic plants with enhanced stress tolerance.
Background: Zymomonas mobilis, as a novel platform for bio-ethanol production, has been attracted more attention and it is very important to construct vectors for the efficient expression of foreign genes in this bacterium. Results: Three shuttle vectors ( pSUZM 1, pSUZM2 and pSUZM3 ) were first constructed with the origins of replication from the chromosome and two native plasmids (pZZM401 and pZZM402) of Z. mobilis ZM4, respectively. The three shuttle vectors were stable in Z. mobilis ZM4 and have 3,32 and 27 copies, respectively. The promoter Ppdc (a), from the pyruvate decarboxylase gene, was clonedinto the shuttle vectors, generatingthe expressionvectors pSUZM1(2, 3)a. The codon-optimized glucoamylase gene from Aspergillus awamori combined with the signal peptide sequence from the alkaline phosphatase gene of Z. mobilis was cloned into pSUZM1(2, 3)a, resulting in the plasmids pSUZM1a-GA, pSUZM2a-GA and pSUZM3a-GA, respectively. After transforming these plasmids into Z. mobilis ZM4, the host was endowed with glucoamylase activity for starch hydrolysis. Both pSUZM2a-GA and pSUZM3a-GA were more efficientatproducingglucoamylase thanpSUZM1a-GA. Conclusions: These results indicated that these expression vectors are useful tools for gene expression in Z. mobilis and this could provide a solid foundation for further studies of heterologous gene expression in Z. mobilis.