A Novel Role of Pipecolic Acid Biosynthetic Pathway in Drought Tolerance through the Antioxidant System in Tomato.

With global warming and water shortage, drought stress is provoking an increasing impact on plant growth, development, and crop productivity worldwide. Pipecolic acid (Pip) is an emerging lysine catabolite in plants, acting as a critical element in disease resistance with a related signal pathway of phytohormone salicylic acid (SA). While SA plays a vital role in various abiotic stresses, the role of Pip in plant response to abiotic stresses, especially drought, remains largely unknown. To address this issue, Pip biosynthetic gene mutants and hydroxylated modification gene mutants were generated using CRISPR-Cas9 gene-editing approaches. Drought resistance dramatically increased in mutants compared with wild-type, which was associated with increased CO assimilation, photosystems activities, antioxidant enzymes activities, ascorbate and glutathione content, and reduced reactive oxygen species accumulation, lipid peroxidation and protein oxidation. On the contrary, mutants were more sensitive to drought, showing damaged photosystems and impaired antioxidant systems, which were significantly alleviated by exogenous ascorbate. Our results demonstrate that Pip biosynthesis and hydroxylated modification pathways play a critical role in drought tolerance through the antioxidant system in tomato. This knowledge can be helpful to breed improved crop cultivars that are better equipped with drought resistance.