Integrated metabolomic and transcriptomic analysis reveals the glycolysis and TCA cycle pathways involved in the occurrence and recovery of tapping panel dryness in Hevea brasiliensis

Tapping panel dryness (TPD) in rubber trees poses a significant challenge to the current production of natural rubber. However, the molecular mechanisms underlying the occurrence and recovery of TPD remain to be elucidated. To address this, we conducted transcriptomic and metabolomic analyses of latex samples from healthy (HL), TPD-affected (TL) and TPD-recovery trees (RL). In total, 539 differentially expressed metabolites (DEMs) and 2598 differentially expressed genes (DEGs) were identified between TL and HL, and 553 DEMs and 2830 DEGs were detected between RL and TL. These DEMs and DEGs were mainly enriched in carbohydrate, amino acid, and fatty acid metabolism. During the occurrence of TPD, the metabolic balance of glycolysis and TCA cycle in latex is disrupted, consequently resulting in the accumulation of glucose and a reduction in the synthesis of metabolites essential for latex regeneration, such as acetyl coenzyme A, adenosine triphosphate, and amino acids. On the contrary, during the recovery of TPD, these metabolites gradually return to normal levels. Further detection of enzyme activities within these two pathways revealed that the activities of hexokinase, pyruvate kinase, pyruvate dehydrogenase, and citrate synthase in latex significantly decreased after TPD occurrence, but returned to normal levels after TPD recovery. These four enzymes might play a crucial role in the onset and recovery of TPD by modulating the synthesis of precursors for natural rubber biosynthesis. Our findings provide new insights into the potential molecular mechanisms underlying the occurrence and recovery of TPD in rubber tree.