Sweet defense: vacuolar transporters strengthen plants under stress
image: A diagram that depicts how VSTs manage the drought resistance in apple plants.
Credit: Horticulture Research
Drought is one of the greatest threats to crop yield and fruit quality worldwide. Researchers have discovered that apples can defend themselves against water shortage by activating vacuolar sugar transporters (VSTs) controlled by the transcription factor MdDREB2A. These genes—MdERDL6-1, MdERDL6-2, MdTST1, and MdTST2—promote the accumulation of soluble sugars, which act as osmotic regulators, maintain leaf water balance, and enhance antioxidant and abscisic acid (ABA) responses. Transgenic apple and Arabidopsis plants overexpressing these genes displayed higher survival, reduced water loss, and improved photosynthesis under drought. The findings suggest a genetic strategy to breed fruit crops with both better drought tolerance and improved sugar content, offering promise for agriculture in increasingly dry climates.
Climate change is intensifying drought episodes that disrupt photosynthesis, damage plant cells, and lead to significant yield losses in horticultural crops. Plants often counteract water scarcity through osmotic adjustment, accumulating sugars and other solutes that stabilize cellular structures and maintain turgor. Previous studies revealed that vacuolar sugar transporters (VSTs) not only regulate fruit sweetness but also respond to environmental stress. However, the detailed molecular mechanisms behind their role in drought adaptation remain unclear. Particularly, the integration between sugar transport and hormonal signaling pathways like abscisic acid (ABA) has not been fully resolved. Based on these challenges, there is a pressing need to investigate how vacuolar sugar transport contributes to drought resistance.
A team from Northwest A&F University and collaborators published (DOI: 10.1093/hr/uhae251) new findings on September 3, 2024, in Horticulture Research. The study reveals how MdDREB2A transcriptionally regulates four vacuolar sugar transporter genes—MdERDL6-1/-2 and MdTST1/2—to boost drought tolerance in apple. By promoting sugar accumulation and activating ABA signaling, these genes enhance water retention, reduce oxidative stress, and support photosynthesis under stress conditions. The work highlights an effective strategy for breeding apple varieties that are both sweeter and more resilient to drought.
The researchers used transcriptome analysis to identify over 4,500 differentially expressed genes in apple leaves under drought, with sugar transporter genes prominently enriched. Four VSTs—MdERDL6-1, MdERDL6-2, MdTST1, and MdTST2—showed markedly higher expression during water deficit. Promoter assays confirmed that MdDREB2A binds to their cis-elements, directly activating their transcription. Functional tests in transgenic apple and Arabidopsis lines demonstrated that overexpression of each VST increased soluble sugar levels, reduced leaf water potential, and improved drought survival. Apple plants overexpressing MdERDL6-1 maintained higher photosynthetic efficiency, reduced transpiration, and exhibited enhanced ROS-scavenging enzyme activity compared to controls. Moreover, these plants accumulated more ABA and upregulated biosynthesis genes such as MdNCED1 and MdNCED3, promoting stomatal closure and reducing water loss. Collectively, the study revealed a regulatory module—MdDREB2A–VST–ABA—that integrates sugar homeostasis with hormonal signaling, enabling plants to endure drought stress while simultaneously enhancing sugar accumulation that contributes to fruit quality.
“This study provides the first direct evidence that VSTs are downstream targets of MdDREB2A in apple,” said Prof. Mingjun Li, corresponding author of the study. “By linking sugar transport, osmotic balance, and ABA signaling, we show how plants can leverage metabolic pathways for stress resilience. Importantly, these findings suggest that manipulating sugar transporters offers dual benefits: improving fruit sweetness and flavor while strengthening drought tolerance. This work opens exciting possibilities for developing climate-resilient horticultural crops through targeted genetic approaches.”
The discovery of the MdDREB2A–VST regulatory pathway holds significant implications for horticultural breeding. Enhancing soluble sugar accumulation not only improves fruit taste but also strengthens stress defenses. By engineering crops to overexpress key transporters, breeders could create varieties with superior resilience to prolonged droughts, reducing losses in regions facing water scarcity. Such crops may also deliver better market value due to enhanced sweetness and quality. Beyond apple, the conserved nature of these genes across species suggests that similar strategies could be applied to other fruit crops, providing a broad approach to securing agricultural productivity under climate stress.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae251
Funding information
This work was supported by the Young Elite Scientists Sponsorship Program by CAST (2023QNRC001), the National Key Research and Development Program of China (2023YFD2301000), the China Postdoctoral Science Foundation (2023 T160536, 2023 M742870), the Shaanxi Association for Science and Technology Young Talents Lifting Project (20230201), and the Shaanxi Postdoctoral Research Funding Project (2023BSHTBZZ24).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.