Unlocking drought-resistant apples through hormone-driven gene networks
image: Proposed model for the role of the MsABI5-MsSMXL1-MsNAC022 cascade in enhancing drought resistance. SLs activate MsABI5 expression during drought stress in Malus sieversii. MsABI5 directly binds to the MsP5CS2.2 promoter and enhances its expression to stimulate proline accumulation and drought resistance. MsABI5 upregulates MsNAC022 expression but negatively regulates MsSMXL1 expression. MsNAC022 directly binds to the MsP5CS2.2 promoter to enhance proline accumulation during drought stress, and MsSMXL1 interacts with MsNAC022 to repress its transactivation activity, thus attenuating drought tolerance in apple. The → indicates activation. The indicates repression. MsABI5 → MsP5CS2.2 indicates MsP5CS2.2 is activated by MsABI5. MsABI5 → MsNAC022 indicates MsNAC022 is activated by MsABI5. MsNAC022 → MsP5CS2.2 indicates MsP5CS2.2 is activated by MsNAC022. MsABI5 MsSMXL1 indicates MsSMXL1 is repressed by MsABI5. MsSMXL1 MsNAC022 indicates the transactivation of MsNAC022 to MsP5CS2.2 expression is repressed by MsSMXL1. Image link: https://academic.oup.com/view-large/figure/521468017/uhaf101f6.tif
Credit: Horticulture Research
Apple (Malus domestica) is a major global fruit crop vulnerable to drought stress, which disrupts photosynthesis, accelerates oxidative injury, and significantly depresses yield. Plants often accumulate proline to maintain osmotic balance under water scarcity, yet the hormone-gene regulatory network that activates proline synthesis remains unclear. Strigolactones and abscisic acid (ABA) are both known to participate in drought signaling, but how their transcriptional outputs interact in apple has not been fully resolved. Understanding this crosstalk is essential for breeding water-efficient, climate-adaptive fruit trees. Given these challenges, deeper research is needed to clarify how hormonal pathways jointly activate drought-tolerance genes in apple.
Beijing, China — On April 9, 2025, researchers from China Agricultural University published (DOI: 10.1093/hr/uhaf101) a study in Horticulture Research revealing a previously unknown mechanism by which strigolactones improve drought tolerance in apple. The team demonstrated that strigolactones activate MsABI5, driving proline biosynthesis through MsP5CS2.2 while suppressing the negative regulator MsSMXL1, thereby enhancing stress adaptation. Integrating physiological experiments, promoter-binding assays, and protein interaction analysis, the work uncovers a hormone-responsive regulatory hub with strong potential for breeding drought-resilient apple cultivars.
Under drought and osmotic stress conditions, GR24 (a synthetic SL analogue) treatment improved leaf turgor, reduced MDA levels, and increased proline accumulation in apple plants. Transgenic experiments confirmed that MsABI5 overexpression enhanced drought tolerance, whereas suppression led to greater stress sensitivity. Molecular assays demonstrated that MsABI5 directly binds to the MsP5CS2.2 promoter, activating its transcription and promoting osmoprotective proline synthesis.
The study further identified MsSMXL1 as a negative regulator whose expression decreases under drought but recovers when MsABI5 signaling is inhibited. Overexpression of MsSMXL1 weakened drought resistance, confirming its repressive function. Protein interaction assays showed that MsSMXL1 physically interacts with the transcription factor MsNAC022, suppressing its transcriptional activation capability. However, deletion of the EAR motif eliminated this repression. Meanwhile, MsABI5 directly induced MsNAC022 expression, forming a coordinated positive drought-response axis.
Together, the researchers established the MsABI5–MsSMXL1–MsNAC022 cascade, where MsABI5 activates MsP5CS2.2 for proline biosynthesis and simultaneously alleviates MsSMXL1-mediated inhibition, allowing MsNAC022 to further enhance stress tolerance.
“Our work illustrates how strigolactones and ABA signaling converge through MsABI5 to orchestrate drought tolerance in apple,” the authors comment. “The discovery that MsABI5 both activates MsP5CS2.2 and suppresses MsSMXL1 — releasing MsNAC022 from transcriptional inhibition — provides a complete regulatory framework for breeding drought-adaptive cultivars. This cascade not only enriches our understanding of hormone crosstalk but also offers precise genetic intervention targets for improving fruit tree stress resilience in the face of climate intensification.”
The clarified regulatory cascade provides actionable molecular targets for engineering drought-resistant apple varieties. Strategies such as CRISPR-mediated activation of MsABI5 or suppression of MsSMXL1 could accelerate breeding of water-efficient rootstocks with stable yield performance. Marker-assisted selection based on MsP5CS2.2 or MsNAC022 expression may further enhance cultivar screening efficiency. As global aridity worsens, leveraging strigolactone-activated defense modules could support sustainable orchard production and resilience in perennial crops. This mechanistic insight may also translate to other woody species, broadening its value across horticultural systems.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf101
Funding information
This work is supported by the Nation Key Research and Development Program of China (Grant No. 2022YFD1200501) and the National Natural Science Foundation of China (Grant No. 32272686), the Construction of Beijing Science and Technology Innovation and Service Capacity in Top Subjects (Grant No. CEFF-PXM2019_014207_000032), and the 2115 Talent Development Program of China Agricultural University.
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.