Oligogalacturonides Operate as Endogenous Elicitors to Regulate Aluminum Tolerance in Pea (<scp><i>Pisum sativum</i></scp>)

Aluminum (Al) toxicity is a major limiting factor leading to crop yield reduction in acidic soils. The pectic polysaccharides, key components of plant cell walls, are considered the primary binding site for Al ions. Oligogalacturonide (OGA), the oligomers of alpha-1,4-linked galacturonosyl residues originating from the degradation of cell wall pectin (homogalacturonan), are able to elicit defense responses and protect plants against biotic stress, such as pathogen infections. However, the involvement of OGA in the plant's response to abiotic stress remains to be elucidated. In this work, we analysed the effects of Al treatment on the endogenous OGA content in pea root tips, as well as the effects of OGA pretreatment on pea root elongation, Al content, and reactive oxygen species (ROS) metabolism, with a working hypothesis being that OGA is causally involved in plant responses to Al toxicity. Hydroponically grown pea (Pisum sativum) plants were used to explore the biological functions of OGA in response to Al toxicity. Our data showed that Al treatment significantly induced the accumulation of endogenous OGA in root tips, primarily in the form of short-chain OGA. Pretreatment with exogenous OGA for 12 h notably improved pea tolerance to Al toxicity, including mitigating Al-induced suppression of root elongation growth and attenuating Al toxicity effects on the root system. OGA also enhanced Al tolerance by regulating redox homeostasis in root tips, reducing Al toxicity-induced accumulation of ROS and by transcriptional upregulation of antioxidant enzyme activities. Overall, this research is the first to demonstrate the role of OGA in plant responses to Al toxicity, offering novel theoretical foundations for understanding plant adaptation to acidic soil conditions.