How apple roots fight chloride overload: ABA’s hidden molecular pathway revealed
image: A working model showing that the ABI5-ZAT10-SLAH3 transcription module mediates ABA to regulate Cl− accumulation and damage under chloride stress.
Credit: Horticulture Research
Chloride toxicity is a growing threat to salt-sensitive crops, causing oxidative stress, membrane damage, and cell death. A recent study reveals that abscisic acid (ABA), a well-known stress hormone, enhances plant tolerance to chloride stress in Malus hupehensis by activating chloride efflux from roots. This mechanism relies on a regulatory pathway involving the transcription factors MhABI5 and MhZAT10L, and the anion channel gene MhSLAH3. By suppressing MhZAT10L, which normally inhibits MhSLAH3, ABA enables the expression of MhSLAH3 and promotes Cl⁻ extrusion. These findings offer new insights into hormone-mediated ionic detoxification, with broad implications for improving salt tolerance in horticultural crops.
Although chloride (Cl⁻) is essential in small amounts, its excess can lead to severe cellular toxicity, particularly in sensitive species like apple, citrus, and grapevine. In plant roots, Cl⁻ uptake is largely passive, while Cl⁻ efflux is actively regulated by membrane-localized channels such as SLAC/SLAH. Prior studies have shown that abscisic acid (ABA) suppresses Cl⁻ accumulation, yet the precise molecular pathway by which ABA enhances Cl⁻ efflux remains elusive. Moreover, how ABA interacts with transcriptional repressors of Cl⁻ transport genes under stress is not well understood. Due to these gaps in knowledge, it is essential to investigate the ABA-mediated molecular framework that regulates chloride efflux and improves plant stress resilience.
Researchers from Shandong Agricultural University have uncovered how ABA promotes Cl⁻ efflux in apple rootstock Malus hupehensis by modulating a transcriptional cascade. The findings (DOI: 10.1093/hr/uhae200) were published on July 24, 2024, in Horticulture Research. The team identified a core regulatory module, the ABI5-ZAT10-SLAH3 pathway, which enables ABA to alleviate Cl⁻-induced cell death by promoting Cl⁻ extrusion. This discovery reveals a previously unknown hormone-transcription channel network that could help engineer chloride-tolerant rootstocks for apple and other fruit crops grown in saline soils.
The study demonstrated that low-dose ABA application (5–10 μM) significantly reduced Cl⁻ accumulation, hydrogen peroxide levels, and cell death in M. hupehensis under chloride stress. Central to this response was the anion channel gene MhSLAH3, which is highly expressed in roots and activated by both Cl⁻ and ABA. Overexpression of MhSLAH3 boosted Cl⁻ efflux and mitigated damage, while its silencing impaired ABA’s positive effects. Yeast one-hybrid and EMSA assays revealed that MhZAT10L, a C2H2-type transcription factor, binds directly to the MhSLAH3 promoter to repress its transcription. Importantly, ABA downregulated MhZAT10L, thereby relieving its suppression of MhSLAH3. Further experiments showed that MhABI5, a key ABA-responsive transcription factor, directly represses MhZAT10L by binding to its promoter. Overexpressing MhABI5 enhanced Cl⁻ efflux, reduced oxidative damage, and upregulated MhSLAH3 expression. Co-overexpression of MhABI5 and MhZAT10L neutralized these benefits, confirming the hierarchy of this regulatory module. The results were validated in both transgenic apple calli and Arabidopsis models, demonstrating the conservation and functionality of this pathway across species.
“Our work provides direct evidence that ABA regulates chloride efflux through a transcriptional cascade involving MhABI5, MhZAT10L, and MhSLAH3,” said Dr. Hongqiang Yang, corresponding author of the study. “This regulatory mechanism reveals how plants fine-tune ion homeostasis under stress, and points to new molecular targets for breeding chloride-tolerant rootstocks. Understanding the ABA signaling architecture could transform how we manage salt-affected horticultural crops.”
This newly identified ABI5-ZAT10-SLAH3 regulatory axis opens promising avenues for genetic improvement of Cl⁻-sensitive crops. By engineering rootstocks with enhanced ABA responsiveness or altered expression of MhSLAH3 or MhZAT10L, breeders could significantly increase crop resilience in saline or chloride-polluted soils. Moreover, the conserved nature of this mechanism across apple and Arabidopsis suggests its broader applicability in other fruit trees and dicots. These insights could support sustainable agriculture on marginal lands and improve productivity in salt-stressed environments, contributing to long-term food security.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae200
Funding information
This work acknowledges the financial support from the National Natural Science Foundation of China (32172517), the National Key Research and Development Program of China (2019YFD1000103), and the Natural Science Foundation of Shandong Province (ZR2023MC003).
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.