Universal Stress Protein (USP) Enhances Plant Growth and Development by Promoting Cell Expansion

Plants are exposed to various environmental stimuli, including abiotic and biotic stresses, during their life cycle. In Arabidopsis thaliana , the Universal Stress Protein (AtUSP) acts as a protein chaperone and RNA chaperone to protect plants from heat shock and cold shock, respectively. This study aimed to explore the role of AtUSP in plant growth and development. We conducted morphological analyses of wild-type (WT; Col-0), AtUSP overexpression (AtUSP OE ), and atusp knockout mutant plants during their vegetative growth, and measured the total leaf number, leaf size, and root length. Compared with the WT, AtUSP OE plants displayed enhanced growth, whereas atusp plants displayed reduced growth of all examined organs. To investigate whether these growth phenotypes were caused by changes in cell expansion and proliferation, we analyzed the mature leaves of all genotypes at the cellular level. The enlarged leaves of AtUSP OE plants showed an increase in cell size, but not in cell number, indicating that AtUSP promotes cell expansion. Moreover, expression analysis of cell growth-related genes revealed that AtUSP is involved in cell expansion rather than cell proliferation. These findings suggest that AtUSP acts as a positive regulator of cell expansion, and provide novel insights into its role in plant growth and development.