A profilin gene promoter from switchgrass (Panicum virgatum L.) directs strong and specific transgene expression to vascular bundles in rice
A switchgrass vascular tissue-specific promoter (PvPfn2) and its 5′-end serial deletions drive high levels of vascular bundle transgene expression in transgenic rice.
Constitutive promoters are widely used for crop genetic engineering, which can result in multiple off-target effects, including suboptimal growth and epigenetic gene silencing. These problems can be potentially avoided using tissue-specific promoters for targeted transgene expression. One particularly urgent need for targeted cell wall modification in bioenergy crops, such as switchgrass (Panicum virgatum L.), is the development of vasculature-active promoters to express cell wall-affective genes only in the specific tissues, i.e., xylem and phloem. From a switchgrass expression atlas we identified promoter sequence upstream of a vasculature-specific switchgrass profilin gene (PvPfn2), especially in roots, nodes and inflorescences. When the putative full-length (1715 bp) and 5′-end serial deletions of the PvPfn2 promoter (shortest was 413 bp) were used to drive the GUS reporter expression in stably transformed rice (Oryza sativa L.), strong vasculature-specificity was observed in various tissues including leaves, leaf sheaths, stems, and flowers. The promoters were active in both phloem and xylem. It is interesting to note that the promoter was active in many more tissues in the heterologous rice system than in switchgrass. Surprisingly, all four 5′-end promoter deletions, including the shortest fragment, had the same expression patterns as the full-length promoter and with no attenuation in GUS expression in rice. These results indicated that the PvPfn2 promoter variants are new tools to direct transgene expression specifically to vascular tissues in monocots. Of special interest is the very compact version of the promoter, which could be of use for vasculature-specific genetic engineering in monocots.
KeywordsPvPfn2 Vascular bundle-specific promoter Serial promoter deletion Stable rice transformation Switchgrass Rice
This study was supported by funding from the BioEnergy Science Center (BESC) to CNS, the National High Technology Research and Development Program (863 Program) of China (no. 2012AA101801-02) to XZ, and China Scholarship Council to WX. We thank the technical support from the UTIA Genomics Hub and the DNA Sequencing Lab at UTK. BESC is a US Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science.
Compliance with ethical standards
All regulations were followed in the research.
Conflict of interest
Some of the authors are inventors of promoter patents, some of which have been licensed by companies. The promoter sequences and their function in plants is the topic of a US patent application, which is assigned to the University of Tennessee Research Foundation.
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