A combinatorial TRM-OFP module bilaterally fine-tunes tomato fruit shape

The mechanisms that regulate the vast diversity of plant organ shapes such as the fruit remain to be fully elucidated. TONNEAU1 Recruiting Motif proteins (TRMs) have been implicated in the control of organ shapes in a number of plant species, including tomato. However, the role of many of them is unknown. TRMs interact with Ovate Family Proteins (OFPs) via the M8 domain. However, the in planta function of the TRM-OFP interaction in regulating shape is unknown. We used CRISPR/Cas9 to generate knockout mutants in TRM proteins from different subclades and in-frame mutants within the M8 domain to investigate their roles in organ shape and interactions with OFPs. Our findings indicate that TRMs impact organ shape along both the mediolateral and proximo-distal axes of growth. Mutations in Sltrm3/4 and Sltrm5 act additively to rescue the elongated fruit phenotype of ovate/Slofp20 (o/s) to a round shape. Contrary, mutations in Sltrm19 and Sltrm17/20a result in fruit elongation and further enhance the obovoid phenotype in the o/s mutant. This study supports a combinatorial role of the TRM-OFP regulon where OFPs and TRMs expressed throughout development have both redundant and opposing roles in regulating organ shape.