GA 2-oxidases regulate gibberellin levels in ovaries and axillary buds of tomato plants and their silencing is responsible for parthenocarpic fruit growth and branching inhibition.Gibberellins (GAs) are phytohormones that regulate a wide range of developmental processes in plants. Levels of active GAs are regulated by biosynthetic and catabolic enzymes like the GA 2-oxidases (GA2oxs). In tomato (Solanum lycopersicum L.) C-19 GA2oxs are encoded by a small multigenic family of five members with some degree of redundancy. In order to investigate their roles in tomato, the silencing of all five genes in transgenic plants was induced. A significant increase in active GA(4) content was found in the ovaries of transgenic plants. In addition, the transgenic unfertilized ovaries were much bigger than wild-type ovaries (about 30 times) and a certain proportion (5-37%) were able to develop parthenocarpically. Among the GA2ox family, genes GA2ox1 and -2 seem to be the most relevant for this phenotype since their expression was induced in unfertilized ovaries and repressed in developing fruits, inversely correlating with ovary growth. Interestingly, transgenic lines exhibited a significant inhibition of branching and a higher content of active GA(4) in axillary buds. This phenotype was reverted, in transgenic plants, by the application of paclobutrazol, a GA biosynthesis inhibitor, suggesting a role for GAs as repressors of branching. In summary, this work demonstrates that GA 2-oxidases regulate gibberellin levels in ovaries and axillary buds of tomato plants and their silencing is responsible for parthenocarpic fruit growth and branching inhibition. We thank Drs Esther Carreras and Jose Luis Garcia-Martinez (IBMCP, Valencia, Spain) for critical reading of the manuscript, and Ana Ahuir, Teresa Sabater, Ingabritt Carlsson, and Eva Segarra for technical support. This work was supported by the Spanish Plan Nacional I+D Biotecnologia [grant BIO2009-07968] and CSIC to LM-B [fellowship JAEPre015]. No conflicts of interest declared. Martínez Bello, L.; Moritz, T.; Lopez Diaz, I. (2015). Silencing C-19-GA 2-oxidases induces parthenocarpic development and inhibits lateral branching in tomato plants. Journal of Experimental Botany. 66(19):5897-5910. https://doi.org/10.1093/jxb/erv300