A research group led by Prof. LIANG Zhenchang from the Institute of Botany, Chinese Academy of Sciences, has uncovered two transcription factors (VvERF105 and VvNAC72) dynamically regulate the gene expression of a hexose transporter (VvSWEET15) that promotes hexose accumulation at different developmental stages in grape berries.
The results of this study were published in The Plant Cell on December 18, 2024.
In fleshy fruits like grapes, apples, pears, and tomatoes, sugar accumulation occurs primarily through an apoplasmic pathway. During the phloem unloading process, sugar transporters are critical in efficiently transferring sugars from the phloem sap into sink organs, where they are utilized for growth, energy storage, and metabolism. This process is essential not only for plant productivity but also for the plants' capacity to act as carbon sinks.
In grapevines (Vitis vinifera L.), VvSWEET15 gene is strongly expressed during berry ripening. However, the specific functions of VvSWEET15 and the mechanisms governing its transcriptional regulation remain poorly understood. This study focused on understanding how VvSWEET15 contributes to sugar accumulation, particularly at the véraison stage, when hexose accumulation rapidly increases.
The researchers identified VvERF105 as a repressor that binds to the LTR-binding element in the VvSWEET15 promoter while VvNAC72 functions as an activator, binding to the CACATG domain in the VvSWEET15 promoter to upregulate its expression and promote hexose accumulation at post-véraison stages. Both transcription factors and VvSWEET15 are preferentially expressed in phloem cells, showing the importance of activator - repressor balance.
Validation in grape berries and tomatoes showed VvSWEET15 over-expression boosts hexose levels, suggesting its potential for improving sugar content in other crops. Additionally, treatment with external glucose and fructose enhanced VvSWEET15 expression, implying a feedback loop that optimizes sugar accumulation.
Interestingly, the study also revealed that while SWEET homologs in other plants, such as Arabidopsis, rice, and citrus, primarily transport sucrose. VvSWEET15 specifically transports hexoses in grapes, highlighting the functional diversification of the SWEET gene family across species.
This study contributes to a better understanding of the mechanisms regulating sugar accumulation in grape berries and offer potential insights into the transcriptional regulation and transport mechanisms of VvSWEET15. This understanding not only pave the way for developing strategies to manipulate ripening processes, with potentially significant implications for the grape and wine industry, but also broader relevance to other fruit crops and offer avenues for breeding varieties with optimized sugar content.
Proposed regulatory model for the inhibition or facilitation of hexose accumulation in grape berries (Image by LU Lizhen).
A research group led by Prof. LIANG Zhenchang from the Institute of Botany, Chinese Academy of Sciences, has uncovered two transcription factors (VvERF105 and VvNAC72) dynamically regulate the gene expression of a hexose transporter (VvSWEET15) that promotes hexose accumulation at different developmental stages in grape berries.
The results of this study were published in The Plant Cell on December 18, 2024.
In fleshy fruits like grapes, apples, pears, and tomatoes, sugar accumulation occurs primarily through an apoplasmic pathway. During the phloem unloading process, sugar transporters are critical in efficiently transferring sugars from the phloem sap into sink organs, where they are utilized for growth, energy storage, and metabolism. This process is essential not only for plant productivity but also for the plants' capacity to act as carbon sinks.
In grapevines (Vitis vinifera L.), VvSWEET15 gene is strongly expressed during berry ripening. However, the specific functions of VvSWEET15 and the mechanisms governing its transcriptional regulation remain poorly understood. This study focused on understanding how VvSWEET15 contributes to sugar accumulation, particularly at the véraison stage, when hexose accumulation rapidly increases.
The researchers identified VvERF105 as a repressor that binds to the LTR-binding element in the VvSWEET15 promoter while VvNAC72 functions as an activator, binding to the CACATG domain in the VvSWEET15 promoter to upregulate its expression and promote hexose accumulation at post-véraison stages. Both transcription factors and VvSWEET15 are preferentially expressed in phloem cells, showing the importance of activator - repressor balance.
Validation in grape berries and tomatoes showed VvSWEET15 over-expression boosts hexose levels, suggesting its potential for improving sugar content in other crops. Additionally, treatment with external glucose and fructose enhanced VvSWEET15 expression, implying a feedback loop that optimizes sugar accumulation.
Interestingly, the study also revealed that while SWEET homologs in other plants, such as Arabidopsis, rice, and citrus, primarily transport sucrose. VvSWEET15 specifically transports hexoses in grapes, highlighting the functional diversification of the SWEET gene family across species.
This study contributes to a better understanding of the mechanisms regulating sugar accumulation in grape berries and offer potential insights into the transcriptional regulation and transport mechanisms of VvSWEET15. This understanding not only pave the way for developing strategies to manipulate ripening processes, with potentially significant implications for the grape and wine industry, but also broader relevance to other fruit crops and offer avenues for breeding varieties with optimized sugar content.
Proposed regulatory model for the inhibition or facilitation of hexose accumulation in grape berries (Image by LU Lizhen).