Manipulation of plant architecture and flowering time by down-regulation of the GRAS transcription factor SlGRAS26 in Solanum lycopersicum

Previous studies suggest that GRAS transcription factors act as essential regulators, not only in plant growth and development but also in response to biotic and abiotic stresses. Recently, 53 GRAS proteins have been identified, but only a few of them have been functionally studied in tomato. Here, we isolated a novel GRAS transcription factor SlGRAS26, its down-regulation generated pleiotropic phenotypes, including reduced plant height with more lateral shoots, internode length, leaf size, even leaflets, accelerated flowering transition and decreased trichome number. Transcription analysis showed that down-regulation of SlGRAS26 altered vegetative growth by suppressing gibberellin (GA) biosynthesis genes and activating the GA inactivating genes, thereby reducing endogenous GA content in transgenic plants. SlGRAS26 may regulate the initiation of lateral buds by regulating the expression of Blind (BL) and BRC1b. The earlier initiation of flower buds in transgenic lines may be controlled by significant up-regulation of SFT, CO1, SBP3, SBP13, and SBP15 genes, related to flowering time. These results demonstrate that SlGRAS26 may play a vital role in the initiation of lateral and inflorescence meristems in tomato.