Overexpression of Vitis GRF4-GIF1 improves regeneration efficiency in diploid Fragaria vesca Hawaii 4

Abstract Background Plant breeding played a very important role in transforming strawberries from being a niche crop with a small geographical footprint into an economically important crop grown across the planet. But even modern marker assisted breeding takes a considerable amount of time, over multiple plant generations, to produce a plant with desirable traits. As a quicker alternative, plants with desirable traits can be raised through tissue culture by doing precise genetic manipulations. Overexpression of morphogenic regulators previously known for meristem development provides an efficient strategy for easier regeneration and transformation in multiple crops. In this study, we show the results for overexpression of chimeric GRF4-GIF1 in diploid strawberry Fragaria vesca Hawaii 4 (strawberry) where Vitis GRF4-GIF1 chimera provides significantly higher regeneration efficiency. Results We present here a comprehensive protocol for strawberry regeneration and transformation under control condition as compared to ectopic expression of GRF4-GIF1 chimeras from different plants. We report that ectopic expression of Vitis vinifera VvGRF4-GIF1 provide significantly higher regeneration efficiency during retransformation over wild-type plants. On the other hand, deregulated expression of miRNA resistant version of Vitis GRF4-GIF1 or TaGRF4-GIF (wheat) resulted in abnormalities. Transcriptomic analysis between the different chimeric GRF4-GIF1 lines indicate that differential expression of FvExpansin might be responsible for the pleiotropic effects. Similarly, cytokinin dehydrogenase/oxygenase and cytokinin responsive response regulators also showed differential expression indicating GRF4-GIF1 pathway playing important role in controlling cytokinin homeostasis. Conclusion Our data indicate that ectopic expression of Vitis vinifera VvGRF4-GIF1 chimera can provide significant advantage over wild-type plants during strawberry regeneration without producing any pleiotropic effects seen for the miRNA resistant VvGRF4-GIF1.