The transcription factor CitZAT5 modifies sugar accumulation and hexose proportion in citrus fruit

The transcription factor CitZAT5 participates in sugar metabolism and transport by regulating CitSUS5 and CitSWEET6, promoting sugar accumulation and increasing hexose proportion in citrus fruit. Sugars are fundamental to plant developmental processes. For fruits, the accumulation and proportion of sugars play crucial roles in the development of quality and attractiveness. In citrus (Citrus reticulata Blanco.), we found that the difference in sweetness between mature fruits of Gongchuan and its bud sport Youliang is related to hexose contents. Expression of a SuS (sucrose synthase) gene CitSUS5 and a SWEET (sugars will eventually be exported transporter) gene CitSWEET6, characterized by transcriptome analysis at different developmental stages of these 2 varieties, revealed higher expression levels in Youliang fruit. The roles of CitSUS5 and CitSWEET6 were investigated by enzyme activity and transient assays. CitSUS5 promoted the cleavage of sucrose to hexoses, and CitSWEET6 was identified as a fructose transporter. Further investigation identified the transcription factor CitZAT5 (ZINC FINGER OF ARABIDOPSIS THALIANA) that contributes to sucrose metabolism and fructose transportation by positively regulating CitSUS5 and CitSWEET6. The role of CitZAT5 in fruit sugar accumulation and hexose proportion was investigated by homologous transient CitZAT5 overexpression, -VIGS, and -RNAi. CitZAT5 modulates the hexose proportion in citrus by mediating CitSUS5 and CitSWEET6 expression, and the molecular mechanism explained the differences in sugar composition of Youliang and Gongchuan fruit.

Automated summary

The transcription factor CitZAT5 plays a role in sugar metabolism and transport in citrus fruit by regulating the genes CitSUS5 and CitSWEET6. This promotes sugar accumulation and increases the proportion of hexose. Sugars are important for plant development, and their accumulation and proportion play crucial roles in the quality and attractiveness of fruits. The difference in sweetness between two varieties of citrus fruit, Gongchuan and Youliang, is related to the expression levels of CitSUS5 and CitSWEET6, with Youliang having higher expression levels.