A proposed model for the role of SlAAP6 in the salt stress response. The roots of tomato exhibit restricted growth and higher accumulation of ROS under salt stress.
Tomatoes are rich in essential metabolites, but their amino acid content, particularly branched-chain amino acids (BCAAs), has changed significantly through domestication. BCAAs such as isoleucine, leucine, and valine are vital for plant development and stress responses, yet their transport mechanisms in tomatoes remain poorly understood. Previous research has shown that amino acid transporters are crucial for nutrient allocation and stress adaptation in other crops, but little was known about their role in tomato salt tolerance. Based on these challenges, a deeper investigation into the genetic control of BCAA transport and its impact on growth and stress resilience was urgently needed.
A research team from Hainan University and Yazhouwan National Laboratory published a on October 11, 2024, in identifying the SlAAP6 gene as a major player in tomato growth and salt tolerance. By conducting a metabolic genome-wide association study and functional characterization, the researchers demonstrated that SlAAP6 mediates the uptake and transport of BCAAs, which in turn enhances biomass accumulation and salinity resistance. Their findings not only clarify a key physiological pathway but also provide valuable targets for tomato genetic improvement.
Using a genome-wide association study involving 374 tomato accessions, the researchers pinpointed SlAAP6 as a gene linked to high BCAA content. Functional assays confirmed that SlAAP6 operates as a high-affinity amino acid transporter localized to the plasma membrane and endoplasmic reticulum. Overexpression of SlAAP6 significantly increased BCAA levels in roots and shoots, promoted biomass accumulation, and elevated nitrogen content, while knockout mutants showed impaired amino acid uptake and reduced growth. Under salt stress, SlAAP6-overexpressing lines displayed stronger root elongation and less reactive oxygen species (ROS) accumulation compared to wild-type and mutant plants. The application of exogenous BCAAs, especially leucine, further boosted the salinity tolerance of SlAAP6-overexpressing plants but failed to rescue the growth defects of mutants. Detailed molecular analyses showed that SlAAP6 activation enhanced the expression of genes related to root proliferation and antioxidant defense, highlighting its dual role in nutrient transport and stress mitigation. This comprehensive study uncovers SlAAP6 as a pivotal factor for improving tomato productivity and resilience under abiotic stress conditions.
“Our findings reveal that the amino acid transporter SlAAP6 is a powerful regulator of both growth and stress tolerance in tomato,” said Professor Shouchuang Wang, corresponding author of the study. “By boosting the accumulation and movement of BCAAs, we can enhance not only plant vigor but also their resilience against challenging environments such as soil salinity. This opens new avenues for breeding strategies focused on improving crop nutrition and sustainability.”
The identification of SlAAP6 as a major regulator of BCAA transport offers promising avenues for developing tomato varieties with enhanced nutritional value, faster growth, and greater tolerance to salt stress. Genetic engineering of SlAAP6 could allow for the production of tomatoes better suited to saline soils, addressing agricultural challenges posed by climate change and soil degradation. Furthermore, this strategy could be extended to other crops where amino acid homeostasis is crucial for optimal yield and stress adaptation, thereby contributing to global food security and sustainable agriculture.
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This work was supported by the Hainan Provincial Natural Science Foundation of China (323CXTD373), the National Key R&D Program of China (No. 2022YFF1001900), the National Natural Science Foundation of China (No. 32100212), the Hainan Province Science and Technology Special Fund (No. ZDYF2022XDNY144), the Hainan Provincial Academician Innovation Platform Project (No. HD-YSZX-202004), the Young Elite Scientists Sponsorship Program by CAST (No. 2019QNRC001), and the Hainan University Startup Fund (No. KYQD (ZR) 21025).
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