Tomato NAC transcription factor NOR-like1 positively regulates tomato fruit softening

Softening is a key factor affecting the quality and shelf life of fleshy fruits and is regulated by transcription factors (TFs). Our previous studies have shown that knockout of the NOR-like1 gene, a NAC transcription factor, can affect fruit ripening and firmness, but the molecular of NOR-like1 regulating fruit softening is not fully understand. Here, we firstly generate the NOR-like1 over-expressing lines (OE-NOR-like1), the result showed that over-expressing NOR-like1 accelerated fruit softening and ripening, affected cell wall structural integrity, and promoted degradation of the middle lamella (ML), resulting in higher levels of water-soluble pectin (WSP) and ionic-soluble pectin (ISP), but lower levels of covalently bound pectin (CSP) and hemicellulose, as compared with WT. Conversely, knockout of NOR-like1 in tomato (CR-NOR-like1) had the opposite effect. RNA-seq (RNA-sequencing) results indicated that NOR-like1 affects the transcriptional levels of genes involved in cell wall metabolism (SlXYL1, SlTBG4 and SlXTH1) and softening-related transcription factors (SlLOB1, SlTAG1 and SlMYB58),. Overall, this study enriches our understanding of transcriptional regulation of softening in tomato fruits and provides new genes for the future selection of new tomato varieties with softening modified through biotechnology.