HbMSL13-mediated mechanotransduction triggers programmed cell death in tapping panel dryness of rubber tree (Hevea brasiliensis)

Tapping panel dryness (TPD) in Hevea brasiliensis is a complex physiological disorder characterized by a reduction or complete cessation of latex flow on the tapping panel of the trunk, which seriously decreases natural rubber yield. Excessive tapping mechanically wounds the bark, triggering programmed cell death (PCD), which is a key mechanism underlying TPD occurrence in rubber trees. However, the key genes involved in transducing mechanical signal and subsequently triggering PCD remain unclear. Here, we selected TPD trees resulting from excessive mechanical tapping as the research material and focused on mechanosensitive ion channels (MSLs) as potential mediators of this process. A total of 22 HbMSL genes were identified in the rubber tree genome. Of them, nine HbMSL genes were expressed in bark tissues, and only HbMSL13 was significantly upregulated during TPD progression. Subcellular localization assays confirmed that HbMSL13 localized to the plasma membrane. Functional characterization via patch-clamp techniques in HEK293T cells demonstrated that HbMSL13 exhibited mechanosensitive ion channel activity in response to mechanical stimulation. Overexpression of HbMSL13 in tobacco induced PCD in phloem cells. Suppression of HbMSL13 in rubber tree protoplasts and its transient overexpression in tobacco leaves revealed that HbMSL13 may function to convert mechanical wounding signal into reactive oxygen species (ROS) signal, thereby triggering PCD. These findings suggest that HbMSL13 may participate in mechanotransduction-mediated PCD following mechanical wounding. Importantly, our results identify HbMSL13 as a key candidate gene for further functional validation in TPD of rubber trees, offering potential strategies for mitigating TPD. This study provides new insights into the molecular mechanisms underlying TPD in rubber trees and may serve as a reference for research on mechanical signal perception and response in industrial crops.