Transcriptome-based analysis reveals key molecular mechanisms and functional characterization of MaCAX3 gene involved in manganese stress responses in mulberry plants.

Background: Manganese (Mn) deficiency and toxicity are major constraints on crop production in soil. Plants have evolved cascade strategies and specific mechanisms to tolerate these stresses. Understanding the molecular mechanisms of tolerance to Mn stress is crucial for improving the efficiency of conferring Mn tolerance and phytoremediation, which is intriguing for evolutionary research on plant adaptation to abiotic stresses. In this study, the responses of mulberry to varied concentration levels of Mn (MnSO), ranging from deficiency (0 mM and 0.03 mM), sufficiency (0.15 mM), and toxicity regimes (1.5 mM and 3 mM) were compared by elucidating the physiological, transcriptome profiling, and functional characterization of the MaCAX3 gene in mulberry leaves.

Results: The results show that Mn-induced deficiency and toxicity not only trigger an increase in oxidation and antioxidant parameters, including hydrogen peroxide (HO), lipid peroxidase (LPO), polyphenol oxidase (PPO), and reactive oxygen species (ROS) but also concomitantly improved the activities of total antioxidant capacity (TAC) and hydroxyl radical (•OH) scavenging levels in mulberry. Results of the cell wall structural components show that cellulose, hemicellulose, and lignin contents were significantly higher, except for pectin, in the control (CK) compared to the deficiency and toxicity. Functional validation of the MaCAX3 gene via gene silencing revealed that the heterologous expression of the MaCAX3 gene increased the transport of Mn in yeast, thus inhibiting the toxic effect of Mn relative to the silenced Macax3-VIGS. Additionally, transcriptome analysis identified a total of 811 differentially expressed genes (DEGs), with 189 and 622 being up- and downregulated, respectively. These DEGs were significantly involved in Mn transport, detoxification, oxidation, antioxidant defense, and cell wall and protein processing, which conferred tolerance to Mn in mulberry plants.

Conclusion: The study sheds substantial light on key molecular mechanisms and the functional characterization and validation of crucial Mn tolerance genes in mulberry leaves.