GmGIF5 Promotes Cell Expansion by Negatively Regulating Cell Wall Modification

Soybean is an important and versatile crop worldwide. Enhancing soybean architecture offers a potential method to increase yield. Plant-specific transcription factors play a crucial, yet often unnoticed, role in regulating plant growth and development. <i>GRF-INTERACTING FACTOR (GIF)</i> genes are plant-specific transcription factors; however, their functions in soybean remain poorly understood. Eight <i>GmGIF</i> members were identified in soybean (<i>Glycine max</i> L.). Phylogenetic analysis divided the eight GmGIF proteins into three groups. In this study, we focused on the role of <i>GmGIF5</i> owing to its high expression level in the meristem. Subcellular localization and transcriptional activity analysis showed that GmGIF5 was localized to the nucleus and has self-transactivation ability. To elucidate the biological function of <i>GmGIF5</i>, we constructed transgenic Arabidopsis lines overexpressing the gene. Phenotype observations indicated that the overexpression of <i>GmGIF5</i> contributed to larger leaves, higher plants, wider stems, and larger seeds. The organs of <i>GmGIF5</i> overexpression lines exhibited larger sizes primarily due to an increase in cell size rather than cell number. RNA sequencing was performed to investigate the underlying mechanism for these effects, showing that differentially expressed genes in overexpression lines were mainly enriched in cell wall modification processes. Our study provides new clues for an understanding of the roles of the <i>GmGIF</i> family in soybean, which can promote the further application of these genes in genetic breeding.