Purple acid phosphatase 10c encodes a major acid phosphatase that regulates plant growth under phosphate-deficient conditions in rice

Whilst constitutive overexpression of particular acid phosphatases (APases) can increase utilization of extracellular organic phosphate, negative effects are frequently observed in these transgenic plants under conditions of inorganic phosphate (Pi) sufficiency. In this study, we identified rice purple acid phosphatase 10c (OsPAP10c) as being a novel and major APase that exhibits activities associated both with the root surface and with secretion. Two constructs were used to generate the OsPAP10c-overexpression plants by driving its coding sequence with either a ubiquitin promoter (UP) or the OsPAP10c-native promoter (NP). Compared with the UP transgenic plants, lower expression levels and APase activities were observed in the NP plants. However, the UP and NP plants both showed a similar ability to degrade extracellular ATP and both promoted root growth. The growth performance and yield of the NP transgenic plants were better than the wild-type and UP plants in both hydroponic and field experiments irrespective of the level of Pi supply. Overexpression of APase by its native promoter therefore provides a potential way to improve crop production that might avoid increased APase activity in untargeted tissues and its inhibition of the growth of transgenic plants.

Identification and Functional Analysis of the psaD Promoter of Chlorella vulgaris Using Heterologous Model Strains

Chlorella has great potential as a bio-factory for production of value-added compounds. To produce the desired chemicals more efficiently in Chlorella, genetic tools for modification of Chlorella need to be developed, especially an endogenous promoter. In this study, the promoter of photosystem I protein D (psaD) from Chlorella vulgaris UTEX395 was identified. Computational analysis revealed the presence of several putative cis-acting elements, including a potential core element, and light-responsive or stress-responsive elements. Gene expression analysis in heterologous expression system in Chlamydomonasreinhardtii and Nicotianabenthamiana showed that CvpsaD promoter can be used to drive the expression of genes. Functional analysis of this promoter suggested that the initiator element (Inr) is important for its function (i.e., TATA-less promoter) and that an additional factor (e.g., downstream of the transcriptional start site) might be needed for light response. We have shown that the CvpsaD promoter is functional, but not sufficiently strong, both in microalgae and higher plant.

An Autoregulated Fine-Tuning Strategy for Titer Improvement of Secondary Metabolites Using Native Promoters in Streptomyces

Streptomycetes are well-known producers of biologically active secondary metabolites. Various efforts have been made to increase productions of these metabolites, while few approaches could well coordinate the biosynthesis of secondary metabolites and other physiological events of their hosts. Here we develop a universal autoregulated strategy for fine-tuning the expression of secondary metabolites biosynthetic gene clusters (BGCs) in Streptomyces species. First, inducible promoters were used to control the expression of secondary metabolites BGCs. Then, the optimal induction condition was determined by response surface model in both dimensions of time and strength. Finally, native promoters with similar transcription profile to the inducible promoter under the optimal condition were identified based on time-course transcriptome analyses, and used to replace the inducible promoter following an elaborate replacement approach. The expression of actinorhodin (Act) and heterogeneous oxytetracycline (OTC) BGCs were optimized in Streptomyces coelicolor using this strategy. Compared to modulating the expression via constitutive promoters, our strategy could dramatically improve the titers of Act and OTC by 1.3- and 9.1-fold, respectively. The autoregulated fine-tuning strategy developed here opens a novel route for titer improvement of desired secondary metabolites in Streptomyces.