Studying the Effect of Dense Planting on the Mechanism of Flower Abscission in Soybean through Combined Transcriptome-Metabolome Analysis

A high pod abscission rate in soybean plants results in a significant decrease in the yield per plant. Under dense planting conditions, dense tolerant soybean cultivars had a relatively low rate of pod abscission, thereby facilitating higher yield. In this experiment, two planting densities were used to analyze the differentially expressed genes and metabolites between the abscised and non-abscised flowers of two soybean cultivars on the basis of transcriptomic and metabolomic techniques. The flower abscission rate of LD32 was significantly lower than that of SND28. Both cultivars were enriched in the photosynthesis, sugar, and starch metabolism; MAPK signaling; and phenylalanine metabolism pathways at different planting densities. However, under dense planting, the trend of differential gene changes in the density-tolerant CV LD32 was opposite to that of the conventional CV SND28. The results of the joint analysis indicated that the co-regulation of cytokinin dehydrogenase 6 (CKX6) and cis-zeatin riboside monophosphate (CZRM) in the zeatin biosynthesis pathway of LD32 under dense planting conditions was the main factor for the relatively low rate of pod abscission under dense planting conditions.