Bioactive gibberellins (GAs) are phytohormones that regulate plant growth and development. DELLA proteins are highly conserved growth repressors that modulate all aspects of GA responses. In this study, an apple MhGAI2 gene, which encoded a DELLA protein, was isolated from the tea crabapple (Malus hupehensis Redh. Var. pingyiensis). MhGAI2-GFP fusion protein was localized in the nucleus. Anti-MhGAI2 antibody was prepared to test GA sensitivity of the MhGAI2 protein. To elucidate the function of MhGAI2, its GA-insensitive gene mhgai2 was artificially generated via a bridge-PCR approach. Subsequently, mhgai2 was genetically transformed into tomato, while transgenic tomato line pBI containing the empty vector pBI121 was used as control. Transgenic tomato lines TL1 and TL2 ectopically expressed mhgai2 transcripts at high levels, and produced GA-insensitive mhgai2 protein. As a result, the seed germination as well as the growth of roots, hypocotyls and seedlings were much more insensitive to exogenous GA₃ application in transgenic tomato lines TL1 and TL2 than pBI control. TL1 and TL2 exhibited smaller plant statures and produced more compacted inflorescences with smaller flowers, fruits and seeds than pBI control. Therefore, mhgai2 ectopic expression affected not only the vegetative growth but also the reproductive development of transgenic tomatoes. In addition, transgenic seedlings were more resistant to drought and salt stress than pBI. In summary, ectopic expression of apple mhgai2 gene caused GA-insensitive phenotypes in tomatoes.
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