Metabolic reconfiguration and proline-mediated responses enhance citrus tolerance to combined water, light and heat stress

• Combined drought, high light, and heat stress triggers a specific metabolic reconfiguration in citrus plants. • Carrizo citrange displays a unique metabolic response to high temperatures, even under combined abiotic stress conditions. • Proline enhances citrus tolerance to combined drought, high light, and heat stress. • Proline treatment boosts antioxidant capacity and activates autophagy in citrus plants. The co-occurrence of multiple abiotic stress factors has become increasingly common in agricultural systems, largely driven by the intensification of climate change. These overlapping stressors not only occur more frequently but also with greater intensity, posing complex challenges to crop resilience and overall productivity. In this context, the ability of plants to adjust their metabolism plays a pivotal role in facilitating acclimation to such multifaceted environmental pressures. The present study explores how two citrus rootstocks with differing stress tolerance profiles—Carrizo citrange and Cleopatra mandarin—reconfigure their primary metabolism when simultaneously exposed to water limitation, high light exposure, and elevated temperatures. Our results demonstrate that Carrizo exhibits distinct metabolic alterations under high temperature stress, whereas Cleopatra remains largely unaffected, suggesting an inherently lower heat tolerance in Cleopatra. Furthermore, Carrizo plants accumulate proline in response to the triple stress combination, while Cleopatra instead accumulates γ-aminobutyric acid (GABA). Remarkably, treatment with exogenous proline enhances stress tolerance in both genotypes by increasing antioxidant enzyme activities and activating autophagy-related stress response pathways. While previous studies have explored plant responses to individual stress factors, our research reveals that metabolic reconfiguration and proline accumulation are key to coping with the combined effects of water deficit, high irradiance, and extreme temperatures in citrus. These findings underscore the pivotal role of proline metabolism in mitigating the detrimental effects of complex abiotic stresses and point to potential strategies for improving citrus adaptation through metabolic modulation. Overall, our study provides valuable insights into the mechanisms driving plant responses to environmental challenges, which are essential for developing sustainable agricultural practices in the face of climate change.