Overexpression of the tomato JOINTLESS gene alters flowering

Abscission is an important mechanism that allows plants to separate unfertilized flowers, ripe fruits or damage organs from the plant. In tomato, jointless (j) and jointless-2 (j-2) mutations leads a lack of abscission zone (AZ) in the flower pedicel, which will avoid falling of ripe fruits and prevent loss of yield. Both J and J-2 are genes encoding MADS-box transcription factors (Mao et al. 2000; Gomez-Roldan et al., 2017) that can interact with other MADS-box proteins, like MACROCALYX (MC), forming a multimeric complex able to regulate the AZ formation (Liu et al. 2014). In addition to the AZ formation, J also plays a role in flowering architecture and meristem fate. This last role is consistent with the functions of the closets homologs of J in Arabidopsis, SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) (Gregis et al. 2006). Mutation of J leads to a faster flower maturation and a reversion to the vegetative state of the inflorescence meristems, which originates leafy inflorescences (Périlleux et al. 2014). Nevertheless, J is not the only one that regulates at the same time AZ formation and meristem functions. Other transcription factors such as the tomato homolog of WUSHEL (LeWUS), GOBLET (GOB), LATERAL SUPPRESSOR (Ls) and Blind (Bl) are involved in those pathways (Nakano et al. 2012; Nakano et al. 2013). We have generated transgenic plants that overexpress J (35S:J) showing changes in the inflorescence architecture and AZ development, but also having interesting phenotypes in axillary development and leaf complexity. These results suggest that J takes part in different pathways and regulate several downstream genes. Our goal is to identify and study the targets of the J transcription factor in order to understand its functions in the tomato plant.