Gibberellin Regulation of Fruit-Set and Growth in Tomato

Abstract

The role of gibberellins (GAs) in tomato (Solanum lycopersicum L.) fruit development was 3 investigated. Two different inhibitors of GA biosynthesis (LAB 198999 and paclobutrazol) 4 decreased fruit growth and fruit-set, an effect reversed by GA3 application. LAB 198999 5 reduced GA1 and GA8 content, but increased that of their precursors GA53, GA44, GA19 and 6 GA20 in pollinated fruits. This supports the hypothesis that GA1 is the active GA for tomato fruit 7 growth. Unpollinated ovaries developed parthenocarpically in response to GA3 > GA1 = GA4 > 8 GA20, but not to GA19, suggesting that GA 20-oxidase activity was limiting in unpollinated 9 ovaries. This was confirmed by analyzing the effect of pollination on transcript levels of SlCPS, 10 SlGA20ox1, -2 and -3, and SlGA3ox1 and -2, encoding enzymes of GA biosynthesis. Pollination 11 increased transcript content of SlGA20ox1, -2, and -3, and SlCPS, but not of SlGA3ox1 and -2. 12 To investigate whether pollination also altered GA inactivation, full length cDNA clones of 13 genes encoding enzymes catalyzing GA 2-oxidases (SlGA2ox1, -2, -3-, -4 and -5) were isolated 14 and characterized. Transcript levels of these genes did not decrease early after pollination (5-d15 old fruits), but transcript content reduction of all of them, mainly of SlGA2ox2, was found later 16 (from 10 d after anthesis). We conclude that pollination mediates fruit-set by activating GA 17 biosynthesis mainly through up regulation of GA20ox. Finally, the phylogenetic reconstruction 18 of the GA2ox familiy clearly showed the existence of three gene subfamilies, and the 19 phylogenetic position of SlGA2ox1, -2, -3, -4 and -5 was established.