HbADF4, an actin-depolymerizing factor, regulates latex flow by modulating actin dynamics in rubber tree

Actin cytoskeleton contributes to diverse cellular processes. The actin-depolymerizing factor (ADF) plays a vital role in regulating actin filament dynamics, and it is one of the widely expressed and highly conserved families of actin-binding proteins (ABPs) that are found in eukaryotic cells. Previous studies have indicated that actin is involved in latex flow in rubber tree. However, the mechanism underlying the regulation of actin dynamics in latex flow remains elusive. Herein, we first found that actin content gradually increased in barks and decreased in latex along with the process of latex flow. Transcriptome data revealed that HbADF4 was highly expressed in latex, suggesting its possible role in latex flow. Therefore, we sought to systemically characterize HbADF4 in this study. The results of genomic sequence, predicted protein structure and phylogenetic analysis revealed that HbADF4 was a member of ADFs belonging to subclass I. The downregulation of HbADF4 caused the elevation of the F/G-actin ratio in latex during the process of the latex flow, whereas the upregulation of HbADF4 with KI and ET treatments caused the decline of the F/G-actin ratio. Furthermore, the transcript level of HbADF4 was related to the various stress and hormone responses in rubber tree. The overexpression of HbADF4 in fission yeast induced the depolymerization of the actin ring, resulting in defective cytokinesis, cell elongation, and the increasing proportion of binucleate/coenocytic cells. Altogether, HbADF4 is associated with stress and hormone responses and is also involved in latex flow by regulating actin dynamics in rubber tree.