# Melatonin Enhances Drought Tolerance by Regulating the Genes Underlying Photosynthesis and Antioxidant Defense in Rubber Tree (Hevea brasiliensis) Seedlings

## TL;DR

Melatonin helps rubber tree seedlings survive drought by boosting photosynthesis and reducing harmful chemicals in the leaves.

## Contribution

This study reveals how melatonin application enhances drought tolerance in rubber trees through gene regulation.

## Key findings

- Melatonin reduces chlorophyll degradation and oxidative stress markers in drought-stressed rubber tree seedlings.
- Transcriptome analysis shows melatonin regulates genes related to photosynthesis and antioxidant defense.
- Common differentially expressed genes are linked to metabolism pathways, suggesting melatonin's role in stress adaptation.

## Abstract

Melatonin (MT) can enhance plant stress tolerance by activating the internal defense system, but its application in rubber trees has been barely reported up to now. In this study, we found that the relative electrical conductivity (REC), H2O2, and malondialdehyde (MDA) contents were significantly higher in the leaves of rubber tree seedlings under drought stress compared to the control (water treatment), whereas chlorophyll contents were obviously lower in the leaves under drought stress compared to the control. MT partly relieves the aforementioned drought-induced adverse effects by dramatically reducing chlorophyll degradation, H2O2 accumulation, MDA content, and REC. Comparative transcriptomes among the PEG (P), MT (M), and PEG + MT (PM) treatments against the control showed that 213, 896, and 944 genes were differently expressed in rubber tree seedlings treated with M, P, and PM in contrast to the control. Among the 64 differently expressed genes (DEGs) being common among the three comparisons, the expression profiles of 25 were opposite in MH compared with PH. Intriguingly, all the KEGG pathways of the DEGs mentioned above belonged to metabolism including energy metabolism, carbohydrate metabolism, amino acid metabolism, and the metabolism of cofactors and vitamins. Exogenous application of MT mainly regulated the genes associated with photosynthesis and the anti-oxidative defense system, thereby enhancing the antioxidant protection of rubber tree seedlings under drought stress. These results suggest that exogenous melatonin application can effectively enhance drought tolerance by heightening ROS scavenging to decrease H2O2 accumulation in rubber tree seedlings. Our results elucidate the molecular mechanisms of MT’s roles in drought stress, which help to employ exogenous MT to boost drought tolerance in the rubber tree.