Spatiotemporal localization of jasmonate in the regulation of fruit set in tomato

TL;DR

A new tomato mutant shows that jasmonate prevents seedless fruit formation by affecting gibberellin levels.

Contribution

A novel tomato mutant reveals jasmonate's role in fruit set through spatiotemporal regulation of gibberellin metabolism.

Findings

The Sldad1 mutant produces seedless fruits without pollination.

Jasmonate accumulates in ovary and ovule before anthesis.

Jasmonate modulates fruit set via gibberellin metabolism.

Abstract

Tomato (Solanum lycopersicum) is a globally important crop, typically requiring pollination for fruit set. Seedless fruit production—fruit set without pollination (parthenocarpy)—is a desirable trait for horticulture, but its molecular mechanisms are not fully understood. Research on tomato fruit set has largely focused on phytohormones such as auxin and gibberellins (GAs), while the role of jasmonic acid (JA) remains unclear. Here, we identified a novel seedless mutant, Sldad1 (Solanum lycopersicum defective in anther dehiscence1) with a mutation in JA biosynthesis induced by ethyl methanesulfonate mutagenesis in the ‘Micro-Tom’ background. The wild type SlDAD1 was found to be specifically transcribed in the stamen filament, particularly 2 d before anthesis, with JA levels correlating to its transcript abundance, as visualized by imaging mass spectrometry. Notably, JA also accumulated in the ovary and ovule before anthesis. The Sldad1 mutant produced seedless fruit without any manual pollination or emasculation and seeded fruit via self-pollination. The mutant showed increased cell expansion, elevated GA levels, and higher transcripts of SlGA20ox3, while treatment to inhibit GA biosynthesis suppressed Sldad1-induced fruit set. Overall, our findings suggest that JA synthesized in the filament accumulates in the ovule before anthesis, thereby preventing tomato fruit set, at least in part, through the modulation of GA metabolism.

The tomato dad1 mutant, defective in jasmonate biosynthesis, produces seedless fruits under normal conditions, and analysis of its expression shows that spatiotemporal localization of jasmonate regulates fruit set primarily by modulating gibberellin metabolism.

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