Auxin‐induced fruit‐set in tomato is mediated in part by gibberellins

Abstract

SummaryTomato (Solanum lycopersicum L.) fruit-set and growth depend on gibberellins (GAs). Auxins, another kind of hormone, can also induce parthenocarpic fruit growth in tomato, although their possible interaction with GAs is unknown. We showed that fruit development induced by the auxins indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid (2,4-D) were significantly reduced by the simultaneous application of inhibitors of GA biosynthesis, and that this effect was reversed by the application of GA 3 . This suggested that the effect of auxin was mediated by GA. Parthenocarpic fruits induced by 2,4-D had higher levels of the active GA 1 , its precursors and metabolites, than unpollinated non-treated ovaries, but similar levels as those found in pollinated ovaries. Application experiments of radioactive-labelled GAs to unpollinated ovaries showed than 2,4-D altered GA metabolism (both biosynthesis and catabolism) in vivo. Transcript levels of genes encoding copalyldiphosphate synthase (SlCPS), SlGA20ox1, SlGA20ox2 and SlGA20ox3, and SlGA3ox1 were higher in unpollinated ovaries treated with 2,4-D. In contrast, transcript levels of SlGA2ox2 (out of the five SlGA2ox genes known to encode this kind of GA-inactivating enzyme) were lower in ovaries treated with 2,4-D. Our results support the idea that auxins induce fruit-set and growth in tomato, at least partially, by enhancing GA biosynthesis (GA 20-oxidase, GA 3-oxidase and CPS), and probably by decreasing GA inactivation (GA2ox2) activity, thereby leading to higher levels of GA 1 . The expression of diverse Aux/indole-3-acetic acid (IAA) and auxin response factors, which may be involved in this effect of auxin, was also altered in 2,4-D-induced ovaries.

Comprehensive Tissue-Specific Transcriptome Analysis Reveals Distinct Regulatory Programs during Early Tomato Fruit Development

“…S6F) are consistent with previous reports of increased bioactive GA content and GA20ox transcription after pollination (Serrani et al, 2007(Serrani et al, , 2008de Jong et al, 2011). However, it was not previously known that a GA20ox transcript increases particularly in the funiculus, which is also a site of high auxin activity (Pattison and Catalá, 2012;Fig.…”

“…9F). Auxin and GA signaling are known to interact during fruit set and development, and it is thought that auxin activity after fertilization induces GA biosynthesis by increasing GA20ox transcription (Serrani et al, 2008). We suggest that up-regulation of GA20ox transcription in the funiculus is controlled by the high auxin activity in this tissue.…”

“…The expression of GA20ox1, GA20ox2, and GA20ox3, which encode GA 20-oxidase, a rate-limiting enzyme, was highest in the funiculus, and two uncharacterized GA20ox homologs showed highest expression in the embryo and endosperm. In contrast, GA2ox4, encoding a GA 2-oxidase that converts bioactive GAs to inactive forms (Serrani et al, 2008), was highly expressed in ovules and placenta in anthesisstage ovaries but was strongly down-regulated in fruit tissues (Supplemental Fig. S6F; Supplemental Table S9).…”

“…However, a comprehensive picture of tissue-specific, auxin-related gene expression to inform models of auxin action in fruit is currently lacking. Moreover, other hormones, including GAs (Serrani et al, 2008), cytokinins (Matsuo et al, 2012), ethylene (LlopTous et al, 2000), and brassinosteroids (Montoya et al, 2005), have been implicated in early tomato fruit development, but details of their spatiotemporal activity and related patterns of gene expression are limited.…”

Seedlessness and Fruit Quality Traits of Gibberellin Induced Parthenocarpic Fruit in Seven Tomato Genotypes (Solanum lycopersicum L.)

“…However, those methods require more time and costs than breeding diploid cultivars of tomato. In order to resolve that problem, plant growth regulator can be used to induce parthenocarpy in tomatoes such as GA 3 (Serrani, Fos, Atarés, & García-Martínez, 2007) and auxin (Serrani, Ruiz-Rivero, Fos, & García-Martínez, 2008). GA 3 had also been widely used in grape (Jung et al, 2014b) and successfully induced parthenocarpic fruit.…”