HbTRXh1 regulates tapping panel dryness occurrence and abiotic stress tolerance by interacting with stress-responsive proteins in rubber tree

Thioredoxins (TRXs) play crucial roles in numerous plant biological processes by catalyzing thiol-disulfide exchanges of their target proteins. However, the functions of TRXs in the rubber tree (Hevea brasiliensis) remain largely unclear. In the present study, we cloned and characterized HbTRXh1, a subgroup I h-type TRX gene from rubber tree. HbTRXh1 contained the typical WCGPC redox-active site and had reductase activity in vitro. Subcellular localization analysis revealed that HbTRXh1 is localized to the plasma membrane, nucleus, and cytoplasm. Expression profiling showed that HbTRXh1 was specifically highly expressed in latex, and its expression was significantly down-regulated in tapping panel dryness (TPD) trees compared with healthy trees. Additionally, HbTRXh1 expression was up-regulated by salt, cold, and drought stresses, whereas it was repressed by oxidative stress and treatments with various hormones (abscisic acid, salicylic acid, methyl jasmonate, and ethylene). Overexpression of HbTRXh1 in yeast and tobacco improved tolerance to various abiotic stresses, including oxidative, salt, and osmotic stresses. RNA-sequencing analysis revealed that overexpression of HbTRXh1 in tobacco altered the expression of genes related to cell wall metabolism, as well as glycine, serine and threonine metabolism. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays demonstrated that HbTRXh1 physically interacted with four stress-responsive proteins (pro-hevein, LEA14, RD19A, and MSH7). These findings suggest that HbTRXh1 is crucial for both TPD occurrence and abiotic stress adaptation in rubber tree, thereby providing a valuable genetic resource for improving TPD tolerance and abiotic stress resistance in rubber tree.