Induction of gibberellin 20-oxidases and repression of gibberellin 2β-oxidases in unfertilized ovaries of entire tomato mutant, leads to accumulation of active gibberellins and parthenocarpic fruit formation

Abstract

In tomato (Solanum lycopersicum L.), auxin and gibberellins (GAs) cross-talk plays an important role during fruit-set. The entire tomato mutant has been previously reported to carry a deletion in the coding region of the SlIAA9 gene, a member of the auxin signal repressor family Aux/IAA. In this paper, we examined the role of ENTIRE gene in controlling GAs metabolism and directing spontaneous fruit initiation and early ovary growth. It was shown that, similarly to pollinated fruits, facultative parthenocarpy in entire depends on active GA metabolism, since fruit growth is suppressed when GA biosynthesis is blocked. Analysis of endogenous GAs during the first 10 days after flower emasculation revealed that entire fruits accumulated higher amounts of active GAs (GA1 and GA3) in comparison to wild type pollinated fruits, suggesting that a different GA homeostasis regulation occurs. Transcript analysis of the main GA biosynthesis genes showed that differently from unpollinated and non parthenocarpic wild type ovaries, in entire active GA flux modulation is regulated by the activation of SlGA20ox1 and SlGA20ox2 and also by a marked reduction of GA catabolism (reduced transcription of GA 2β-oxidase genes) during the early fruit expansion phase.