Effects of decapitation on yield-related traits of total node number per plant in soybean

Context or problem: Decapitation causes axillary bud outgrowth in plants, but the effects of decapitation on yieldrelated traits in soybean (Glycine max) and the underlying mechanisms are not completely clear. Such information would be useful for developing strategies for breeding soybean cultivars with varying degrees of shoot branching in different production systems. Objectives: We aimed to identify the effects of decapitation on axillary bud outgrowth in soybean, including effects on yield-related traits and gene expression. Methods: We examined changes in yield-related traits, including plant height, branch number, node number per single branch and stem, and total node number per plant, in decapitated soybean plants grown in the field and under artificial conditions. We examined these traits in three soybean varieties with different plant architectures grown under normal and dense planting conditions. We also identified differentially expressed genes between decapitation and control conditions to explore the molecular mechanism underlying the effects of removing apical dominance on soybean. Results: Decapitation promoted bud outgrowth in soybean, which increased total node number per plant, thereby improving yields. This effect depended on both the cultivar and planting density. Genes related to phytohormones that inhibit bud outgrowth, such as the strigolactone- and auxin biosynthesis-related genes CAROTENOID CLEAVAGE DIOXYGENASE 8/MORE AXILLARY BRANCHING 4 and YUCCA 8, respectively, were downregulated in response to decapitation treatment. Conversely, genes related to phytohormones that promote bud outgrowth, such as cytokinin biosynthesis-related isopentenyltransferase genes and brassinosteroid signaling pathway genes XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE 23 s, were upregulated after decapitation. Conclusions: Branch architecture is controlled by both genetic and environmental factors. Removing apical dominance at the early seedling stage increased the formation of long branches in some varieties, thereby increasing pod number, seed number, and grain yield per plant. Decapitation caused axillary bud outgrowth, at least in part, by regulating the expression of various genes involved in plant hormone signal transduction and biosynthesis. Implications or significance: These results provide a theoretical basis for the effect of decapitation on soybean yield. In addition, they shed light on the molecular mechanism of axillary bud outgrowth and branch development in soybean, laying the foundation for improving plant architecture via breeding.