Conserved and novel roles of the bHLH transcription factor SPATULA in tomato.

Abstract

Arabidopsis has served as a model plant for studying the genetic networks that guide gynoecium development. However, less is known about other species such as tomato, a model for fleshy fruit development and ripening. Here, we study in tomato the transcription factor SPATULA (SPT), a bHLH-family member that in Arabidopsis is known to be important for gynoecium development. We analysed the expression of SlSPT during flower and fruit development, and its interaction with proteins previously reported as interactors of AtSPT in the gynoecium. We also generated and characterised loss-of-function tomato lines using CRISPR-Cas9. The results show that SlSPT forms homodimers and partially conserves the interactions reported in Arabidopsis with some HECATE proteins, and has a role in floral organ development, particularly in stamen fusion, style and stigma development, and trichome formation on the carpels. Furthermore, lack of SlSPT causes altered exocarp pigmentation. A metabolomic analysis of the exocarp showed perturbations in several pathways in the slspt mutant, with the flavonoid biosynthesis being the most affected, which could potentially impact the nutritional value of the fruit. In summary, the results show conserved functions during gynoecium development and novel roles that enrich the knowledge of the SPT gene in fleshy fruits.