Supplementation of natural light duration promotes accumulation of sugar and anthocyanins in apple (Malus domestica Borkh.) fruit

Light is an environmental factor that is indispensable for plant growth and development. For fruit crops, prolonged light duration promotes fruit coloration and generally increases sugar accumulation, which improve the fruit appearance and flavor quality. Apple (Malus × domestica Borkh.) is a photophilic species for which the yield, fruit appearance, and flavor quality are strongly associated with the light environment. However, few studies have investigated the effect of modifying the light duration in a field environment on apple fruit quality. In this study, we used LED lighting to extend the light duration in an apple orchard after sunset and examined the effect on fruit quality. Strikingly, extending the light duration significantly promoted anthocyanins synthesis in the fruit skin and accumulation of soluble sugars in the fruit flesh. Based on RNA-sequencing results, we screened the MdWRKY40 transcription factor that regulates anthocyanins transport in the skin, and the MdMYB108 transcription factor that regulates sugar accumulation in the flesh. Functional analyses showed that MdWRKY40 could bind to the promoter of MdGSTF12 to promote the transport and accumulation of anthocyanins in the fruit skin. MdMYB108 couldbind to the promoter of MdPFK to promote the accumulation of soluble sugar in the fruit flesh. These findings provide valuable insight into the effect of regulation of the light environment on apple fruit quality, and will be crucial for determining the foremost apple-producing areas and the optimal growth environment.