Mutation in the diageotropica (dgt) gene alters gibberellin metabolism in pollinated tomato fruit

MIGNOLLI, F.; MARIOTTI, L.; LOMBARDI, L.; VIDOZ, M.L.; CECCARELLI, N.; PICCIARELLI, P.

Mar del Plata

Congreso; XXIX Reunión Argentina de Fisiología Vegetal; 2012

Tomato fruit-set and growth depend on the cross-talk among plant hormones, especially auxin and gibberellins (GAs). Although, most of the action of auxin is mediated by GAs, the exact molecular mechanism for auxin regulation of GA-biosynthesis is not known. The low auxin sensitivity exhibited by the diageotropica (dgt) tomato mutant reduces ovary growth during early stage of fruit development. If an attenuated auxin-responsiveness in dgt ovary affects GA biosynthesis and/or signaling and concurs to the reduced fruit growth is under study. Fruits were collected at 0, 2, 4, 6, 8, 10 days after pollination (DAP) and endogenous GA19, GA20, GA1, GA3, GA29 and GA8 were analyzed through gas chromatography/mass spectrometry. In addition, relative expression levels of GAs biosynthesis (GA20-oxidases, GA3-oxidases) and catabolism (GA2-oxidases) genes weredetermined by Real-Time PCR. Levels of GA1 and GA3 (bioactive GAs) and GA8 (the GA1 catabolite) increased in dgt during the first two days. With an opposite trend, wild type fruits steadily accumulated higher contents of GA1 and GA8 from the fourth day after pollination.Transcript levels of GAs biosynthesis genes showed that dgt SlGA20ox1 transcripts were slightly higher during the first four days but did not peak at 8 days after pollination as in wild type fruits. Moreover, the dgt mutant accumulated an elevated relative quantity of SlGA3ox1 mRNA at 0, 2 and 4 days after pollination but dropped later on. Among GA2-oxidase gene family, SlGA2ox5 appeared highly induced in wild type from 4 DAP but very low in dgt. All data revealed that DGT mediated auxin signaling is at least in part involved in the regulation of GAs biosynthesis in fruits.Interestingly, DGT seemed to exert a negative regulation in GA biosynthesis, mainly through GA3-oxidases activity in pre- and post-pollination (up to 48h). Conversely, GA metabolism activation later during fruit development appeared partially hindered by the lack of functional DGT gene.