Identification and application of an exocarp-preferential promoter for genetic engineering of tomato fruit

Tomato () is a globally cultivated crop with great economic value. The exocarp determines the appearance of tomato fruit and protects it from various biotic and abiotic challenges at both pre-harvest and post-harvest stages. However, no tomato exocarp-specific promoter is currently available, which hinders exocarp-based genetic engineering. Here, we identified by RNA sequencing and reverse transcription-quantitative PCR analyses that the tomato gene () was abundantly and predominantly expressed in the exocarp. A fluorescent reporter expressed by a 2087-bp promoter () was mainly detected in the exocarp of transgenic tomato plants of both Ailsa Craig and Micro-Tom cultivars. This promoter was further utilized for transgenic expression of and in tomato, which are master regulators of anthocyanin and cuticular wax biosynthesis, respectively. -driven expression resulted in anthocyanin accumulation in the exocarp, conferring gray mold resistance and extended shelf life to the fruit, while expression led to waxy thickening in the fruit skin, delaying water loss and also extending fruit shelf life. Intriguingly, and two other weaker tomato exocarp-preferential promoters exhibited coincided expression specificities in the gynophore of transgenic () plants, providing not only an inkling of evolutionary homology between tomato exocarp and gynophore but also useful promoters for studying gynophore biology in . Collectively, this work reports a desirable promoter enabling targeted gene expression in tomato exocarp and gynophore and demonstrates its usefulness in genetic improvement of tomato fruit quality.