MicroRNA1917-CTR1-LIKE PROTEIN KINASE 4 impacts fruit development via tuning ethylene synthesis and response

MicroRNA1917 (miR1917) is a newly identified miRNAs that regulate ethylene responses in tomato. However, evidence is still limited about its functions in fruit development and ripening. Here, we investigated the possible roles of miR1917-SlCTR4 module in tomato fruit development. We generated miR1917 knock-down mutants by expressing Short Tandem Target Mimic (STTM1917). qRT-PCR and northern-blot analyses suggested that the expression of miR1917 are down-regulated in STTM1917. Concomitantly, miR1917-targeted SlCTR4 gene was up-regulated. STTM1917 plants showed a series of developmental phenotypes, including larger biomass, longer terminal leaflet, bigger floral organ and enhanced fruit and seed size. RNA-seq and qRT-PCR analyses suggested that the expression levels of numerous miRNAs and genes in the transgenic line were significantly altered compared to the wild type. These miRNAs and genes include fruit development-related miRNAs, fruit ripening-related transcription factors and ethylene metabolism genes. Altogether, our results demonstrated that working in concert with ripening regulators, miR1917 might regulate multiple genes in ethylene pathway, thereby modulating fruit development. Our results further indicated that fine-tuning miRNAs expression via STTM can be deployed for agronomic improvement of tomato.