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Title: TRANSGENE EXPRESSION IN DIPLOID AND OCTOPLOID STRAWBERRIES DRIVEN BY A HETEROLOGOUS PHLOEM-SPECIFIC PROMOTER

Author
item Zhao, Yan
item LIU, QINGZHONG - SHANDONG PR CHINA
item Davis, Robert

Submitted to: Plant Cell Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2004
Publication Date: 10/1/2004
Citation: Zhao, Y., Liu, Q., Davis, R.E. 2004. Transgene expression in diploid and octoploid strawberries driven by a heterologous phloem-specific promoter. Plant Cell Reports. 23:224-230.

Interpretive Summary: Strawberry is susceptible to diseases caused by phytoplasmas, a group of cell wall-less bacteria that are restricted to vascular system in diseased plants. Phytoplasma infection results in heavy fruit loss as well as plant death. An objective of our program is to develop strategies for improving strawberry resistance to phytoplasmas through genetic engineering. One such strategy involves introducing a gene that produces a protein that helps the plant ward off diseases and is active only in the parts of the plant where the phytoplasmas occur. Toward achieving this goal, we devised a DNA molecule consisting of two parts: one part contains a control element that determines the location where a gene will be active and the other part is equipped with a gene that gives a visual signal when the gene is active. We also developed a means to introduce the DNA molecule into strawberry plants. In the genetically modified strawberry plants, the visual signal showed that the introduced gene was active only in the places where the phytoplasmas inhabit. These results suggest that the new DNA molecule and the genetic engineering protocol may be useful for engineering phytoplasma-resistant strawberry plants. The findings will be of greatest interest to research scientists and professionals in plant biotechnology.

Technical Abstract: Strawberry (Fragaria ssp) is susceptible to diseases caused by phytoplasmas, a group of cell wall-less, mycoplasma-like organisms restricted to sieve elements in the phloem tissue of infected plants. Phytoplasmal diseases can result in heavy fruit loss as well as plant death. An objective of our program is to develop strategies for improving strawberry resistance to phytoplasmas via genetic engineering. One such strategy involves phloem-specific expression of anti-apoptotic and anti-microbial peptide genes in engineered strawberry plants. To achieve targeted and efficient phloem-specific expression in strawberry, we constructed a binary vector with an expression cassette bearing the ß-glucuronidase reporter gene (gus) under the control of the promoter of the Arabidopsis sucrose-H+ symporter gene (AtSUC2). Transgenic lines of diploid and octoploid ever-bearing strawberry cultivars were generated with high efficiencies by a novel Agrobacterium-mediated leaf segment transformation protocol. PCR and DNA gel blot analyses confirmed the integration of the foreign gene into transgenic strawberry plants. Histological GUS activity indicated that the reporter gene was expressed specifically in the phloem system of leaves, petioles, and roots of all transgenic lines. These results suggest that the newly established transformation protocol and the AtSUC2 promoter may be useful for engineering phytoplasma-resistant transgenic strawberry plants.