Transcriptional profile and miR164 regulation of tomato AtORE1 ortholog candidates.

The NAC (NAM/ATAF/CUC) transcription factors (TF) comprise an extensive family involved in the regulation of a wide spectrum of processes such as morphogenesis, embryogenesis, stress response, cell division and cell wall thickening. In particular, the Arabidopsis thaliana senescence inducing AtORE1 is known to be positively regulated by ethylene, ABA and darkness, while miR164 is a well-established negative regulator. Moreover, by the direct interaction with GLK TFs, which are essential for chloroplast development and maintenance, AtORE1 shifts 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 impact of leaf senescence regulation over freshly fruit development and ripening is also scarce. By a comprehensive phenetic analysis, three tomato sequences, named SlORE1S02, SlORE1S03 and SlORE1S06, were selected as AtORE1 ortholog candidates. By in silico sequence analysis, SlORE1S03 and SlORE1S06 were predicted to be miR164 targets, while an insertion in SlORE1S02 seems to be disrupting the binding site. Here, the transcript profile of these genes was evaluated upon leaf senescence induction by hormonal, salt or dark treatments. Additionally, the miR164 regulation was addressed by identification of cleaved transcripts and; by qPCR analysis in tomato miR164-overexpressing transgenic lines.