A NAC transcription factor, NOR-like1, is a new positive regulator of tomato fruit ripening

• Published in: Horticulture research 2018-12, Vol.5 (1), p.75-18
• Main Authors: Gao, Ying, Wei, Wei, Zhao, Xiaodan, Tan, Xiaoli, Fan, Zhongqi, Zhang, Yiping, Jing, Yuan, Meng, Lanhuan, Zhu, Benzhong, Zhu, Hongliang, Chen, Jianye, Jiang, Cai-Zhong, Grierson, Donald, Luo, Yunbo, Fu, Da-Qi
• Format: Article
• Language: English
• Subjects: 631/449; 631/61; Agriculture; Biomedical and Life Sciences; Biosynthesis; Cell walls; Chlorophyll; Chromatin; CRISPR; Ecology; Electrophoretic mobility; Ethylene; Fruits; Gene expression; Gene sequencing; Gene silencing; Genes; Immunoprecipitation; Life Sciences; Lycopene; Metabolism; Plant Breeding/Biotechnology; Plant Genetics and Genomics; Plant Sciences; Proteins; Ribonucleic acid; Ripening; RNA; Solanum lycopersicum; Tomatoes; Transcription factors; Viruses
• ISSN: 2052-7276; 2052-7276
• DOI: 10.1038/s41438-018-0111-5

Ripening of the model fruit tomato ( Solanum lycopersicum ) is controlled by a transcription factor network including NAC (NAM, ATAF1/2, and CUC2) domain proteins such as No-ripening (NOR), SlNAC1, and SlNAC4, but very little is known about the NAC targets or how they regulate ripening. Here, we conducted a systematic search of fruit-expressed NAC genes and showed that silencing NOR-like1 (Solyc07g063420) using virus-induced gene silencing (VIGS) inhibited specific aspects of ripening. Ripening initiation was delayed by 14 days when NOR-like1 function was inactivated by CRISPR/Cas9 and fruits showed obviously reduced ethylene production, retarded softening and chlorophyll loss, and reduced lycopene accumulation. RNA-sequencing profiling and gene promoter analysis suggested that genes involved in ethylene biosynthesis ( SlACS2 , SlACS4 ), color formation ( SlGgpps2 , SlSGR1 ), and cell wall metabolism ( SlPG2a , SlPL , SlCEL2, and SlEXP1 ) are direct targets of NOR-like1. Electrophoretic mobility shift assays (EMSA), chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR), and dual-luciferase reporter assay (DLR) confirmed that NOR-like1 bound to the promoters of these genes both in vitro and in vivo, and activated their expression. Our findings demonstrate that NOR-like1 is a new positive regulator of tomato fruit ripening, with an important role in the transcriptional regulatory network. Crop genetics: novel gene involved in tomato ripening Chinese researchers have identified a new gene which regulates the ripening of tomatoes. Several genes known to control tomato ripening are members of the NAC family of regulators. To identify others, a team led by Daqi Fu of China Agricultural University blocked the expression of candidate NAC genes. The discovered that silencing NOR-like1 repressed ripening, leaving the tomatoes partially green. The team also engineered plants with defective copies of NOR-like1 and found that this delayed ripening and eventually resulted in partially ripe fruit and impaired seed development. RNA sequencing of these lines revealed that NOR-like1 directly regulates genes involved in ethylene synthesis, carotenoid accumluation, chlorophyll metabolism, and cell wall breakdown. These findings clearly demonstrate a key role for NOR-like1 as a positive regulator of tomato ripening and a potential tool for controlling this important process.