Small Ubiquitin-like Modifier (SUMO) modification is a crucial post-translational modification of plant proteins, which regulates protein function by covalently attaching a SUMO protein, consisting of approximately 100 amino acids, to the substrate protein through the sequential action of SUMO El activating enzyme, SUMO E2 conjugating enzyme, and SUMO E3 ligase. The addition of SUMO can significanly alter the stability, activity, and localization of the target protein, thereby participating in the precise regulation of plant growth, development, and stress responses.

SIZ1 is a SUMO E3 ligase that plays a vital role in regulating plant growth, development, and stress responses by modulating the SUMOylation of diverse substrate proteins. Although the functions of SIZ1 have been extensively studied in model herbaceous plants such as Arabidopsis thaliana and Oryza sativa, its biological roles in woody plants remain poorly understood.The secondary cell wall (SCW) is a critical component of wood that determines its physical properties. Arabidopsis siz1 mutants exhibit noticeable defects in SCW formation, and SIZI-mediated SUMOylation promotes SCW formation in Arabidopsis. However, whether the SIZI involved in SCW formation or has other biological functions in trees is not well understand.

In this study, we aim to investigate the function of SIZ1 in Populus trichocarpa by generating knockout mutants. We will explore whether SIZI-mediated SUMOylation regulates SCW formation, stress responses, and hormone signaling pathways in poplar. Investigating the function of SIZ1 in poplar will enhance our understanding of tree growth and development, SCW formation, and response to stress.