Apple (Malus domestica) is a major fruit crop, but its perennial growth habit makes stress adaptation especially important. In saline–alkaline regions, high pH and ion toxicity reduce root vitality, impair photosynthesis, and threaten fruit yield and quality. Strigolactones (SLs) are known to shape plant architecture and help plants respond to drought, cold, nutrient shortage, and salt-related stress, yet their role in alkaline-salt tolerance in woody crops has remained unclear. The function of Alkali Tolerance 1 (AT1) homologs has also been studied mainly in annual cereals, leaving a gap in apple biology and stress-resistance breeding. Based on these challenges, there is a need to investigate how SL signaling regulates alkaline-salt tolerance in apple.
A research team from Qingdao Agricultural University, Guizhou University, and Qingdao Academy of Agricultural Sciences published (DOI: 10.1093/hr/uhag089) the findings on March 11, 2026, in Horticulture Research. Using apple seedlings, hormone treatments, and transgenic materials, the team found that the SL analog GR245DS improves alkaline-salt tolerance by activating a MdD53–MdbHLH1–MdAT1 signaling module. Their work connects hormone perception with transcriptional regulation and reactive oxygen species (ROS) control, showing how apple plants translate an external soil stress into cellular protection. The findings place a familiar plant hormone in a new orchard-relevant stress context.
The team first treated Malus hupehensis seedlings with 50 millimolar alkaline salt, 1 micromolar GR245DS, and 10 micromolar TIS108, an SL biosynthesis inhibitor. GR245DS reduced wilting, preserved root length and dry biomass, and strengthened root activity, whereas TIS108 intensified stress injury. Staining assays and biochemical measurements showed that SL treatment lowered hydrogen peroxide (H2O2), superoxide anion (O2·−), and malondialdehyde (MDA), while increasing antioxidant enzyme activity. To find the regulatory switch behind this response, the researchers used RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA), identifying MdbHLH1 as a key alkaline-salt- and SL-responsive transcription factor from a shared set of 102 core response genes. MdbHLH1-overexpressing apple plants showed lower wilting rates and less ROS accumulation than wild-type plants. Yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), and dual-luciferase (Dual-LUC) tests confirmed that MdbHLH1 directly binds and activates the promoter of MdAT1. Additional experiments showed that overexpression of MdAT1 reduced H2O2 content to about half the level observed in wild-type plants. Protein-interaction assays then showed that MdD53 binds MdbHLH1 and suppresses this activation. When SL signaling promotes MdD53 degradation, MdbHLH1 is released to activate MdAT1, enabling stronger redox homeostasis under stress.
The authors said the study reveals a stress-response chain that begins with hormone signaling and ends with a measurable reduction in oxidative damage. They said the key advance is not only identifying MdAT1 as an apple alkaline-tolerance gene, but also showing how its activation is controlled upstream. In this model, MdD53 works like a brake, MdbHLH1 works like a switch, and SL signaling removes the brake so the plant can respond more effectively to alkaline-salt pressure. This makes the pathway both mechanistically informative and potentially useful for crop improvement, rather than a single defensive reaction.
The findings provide practical candidate targets for breeding or engineering apple materials better suited to saline–alkaline soils. Modulating MdbHLH1, MdD53, or MdAT1 could help develop plants with stronger roots, lower ROS accumulation, and improved survival under high-pH stress. Because fruit trees are long-lived crops, early stress tolerance can have lasting effects on orchard establishment, canopy development, and future productivity. The pathway also offers a useful framework for studying SL-mediated stress responses in other woody plants, especially where redox homeostasis, root vigor, and alkaline-salt adaptation remain poorly understood. Future work could test whether this module interacts with ion balance and other hormone pathways under field conditions, and whether natural variation in these genes can support marker-assisted selection.
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References
DOI
10.1093/hr/uhag089
Original Source URL
https://doi.org/10.1093/hr/uhag089
Funding information
This work was supported by the National Natural Science Foundation of China (32472717) and Funds for Modern Agricultural Industry Technology System in Shandong Province, China (SDAIT-06-06).
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.