Tomato AtORE1 ortholog silencing impacts leaf photosynthesis and fruit metabolism.

The NAC (NAM/ATAF/CUC) transcription factors (TF) comprise an extensive family involved in the regulation of a wide spectrum of processes. In particular, the Arabidopsis thaliana AtORE1 is known to be a key trigger for leaf senescence initiation, additionally, this protein physically interacts with GLK TFs, which are essential for chloroplast development and maintenance, preventing their activity of target upregulation. Thus, AtORE1shifts the signal from chloroplast maintenance towards deterioration. Up to date, only 5 out of 101 tomato (Solanum lycopersicum) putative NAC TFs were studied. Additionally, the knowledge regarding the impact of leaf senescence regulation over freshly fruit development and ripening is also scarce. In this context, we aimed to gain further insight into how leaf senescence affects tomato fruit growth and metabolism by identifying and modulating tomato AtORE1 ortholog. The search for AtORE1 ortholog in tomato genome led to the identification of three candidates, namely SlORE1S02, SlORE1S03 and SlORE1S06. By in silico sequence analysis, transcript sequencing and in vivo mRNA profile of tomato transgenic lines overexpressing miR164, we verified that SlORE1S03 and SlORE1S06 were miR164 targets, but not SlORE1S02, possibly by an insertion that disrupted the binding site. Additionally, the three putative orthologs are capable of physically interact with both SlGLKs. Since all three candidates are similarly regulated except for SlORE1S02, we have generated tomato knockdown lines for this gene. The transgenic lines had, at least, 54% less transcripts in non-senescent leaves, which also displayed an increase in SlGLK1 mRNA levels and enhanced carbon assimilation. Maintaining detached leaves in dark induced senescence in non- transgenic lines, but not in SlORE1S02-knockdown lines. Collectively, these data indicate that the manipulation of SlORE1S02 altered the leaf senescence process, so we addressed the impacts over fruit development and metabolism. As major sinks, it would be reasonable to hypothesize that the above described alterations would enhance fruit metabolism. Indeed, for instance, the pericarp of ripe fruits had an increase in soluble solid (Brix) content. In summary, we have characterized the regulation of a still unknown tomato NAC TF that is involved in leaf senescence initiation and addressed its physiological role in vegetative and fruit development.