Martínez-Bello Liliam, Moritz Thomas, López-Díaz Isabel
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia (UPV)-Consejo Superior de Investigaciones Científicas (CSIC), Ingeniero Fausto Elio s/n, 46022 Valencia, Spain.
Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Science, S-90183 Umeå, Sweden.
J Exp Bot. 2015 Sep;66(19):5897-910. doi: 10.1093/jxb/erv300. Epub 2015 Jun 19.
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.) C19 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 GA4 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 GA4 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.
赤霉素（GAs）是一类植物激素，可调控植物广泛的发育过程。活性赤霉素的水平由生物合成和分解代谢酶如GA 2-氧化酶（GA2oxs）来调节。在番茄（Solanum lycopersicum L.）中，C19 GA2oxs由一个由五个成员组成的小多基因家族编码，存在一定程度的冗余。为了研究它们在番茄中的作用，诱导了转基因植物中所有五个基因的沉默。在转基因植物的子房（卵巢）中发现活性GA4含量显著增加。此外，转基因未受精的子房比野生型子房大得多（约30倍），并且一定比例（5 - 37%）能够单性结实。在GA2ox家族中，基因GA2ox1和GA2ox2似乎与这种表型最为相关，因为它们的表达在未受精的子房中被诱导，而在发育中的果实中被抑制，与子房生长呈负相关。有趣的是，转基因株系表现出显著的分枝抑制，并且腋芽中活性GA4含量更高。在转基因植物中，通过施用多效唑（一种GA生物合成抑制剂）可逆转这种表型，这表明GA作为分枝的抑制因子发挥作用。总之，这项工作表明GA 2-氧化酶调节番茄植株子房和腋芽中的赤霉素水平，它们的沉默导致了单性结实果实生长和分枝抑制。
