JsSAMDC promotes polyamine synthesis and flowering genes to synergistically regulate female flower bud differentiation.

The JsSAMDCs promotes the expression of polyamine synthesis genes and regulates the expression of flowering genes which in turn promotes the differentiation of female flower buds in Juglans sigillata Dode. Juglans sigillata is a typical dioecious plant, and its low female-to-male ratio has been a significant factor limiting J. sigillata yield. As a key rate-limiting enzyme in polyamine synthesis, the role of S-adenosylmethionine decarboxylase (SAMDC) in flower bud differentiation is unknown. In this study, we identified seven JsSAMDC genes in the J. sigillata genome. Transcriptome and metabolome data showed that JsSAMDC1 exhibited significant co-expression connectivity, and had a significant positive correlation with the flowering genes CO and SOC1. Concomitantly, higher levels of spermine (Spm) were detected in female flower buds. Exogenous Spm significantly increased the expression levels of these flowering genes and Spm content in female flower buds. JsSAMDC1 encodes a hydrophilic protein dominated by irregular coils in its secondary structure, lacking both a transmembrane region and a signal peptide. The protein localizes to the nucleus, cytoplasm, and plasma membrane. Spatiotemporal expression analysis revealed predominant expression of JsSAMDC1 during the physiological differentiation of female flower buds. Transient silencing of JsSAMDC1 resulted in reduced expression of polyamine biosynthesis and flowering-related genes, decreased content of putrescine (Put) and spermidine (Spd) in flower buds, and promoted Spm accumulation. Overall, JsSAMDC1 and polyamine biosynthesis genes synergistically elevate Spm levels in female flower buds and, together with the flowering genes CO and SOC1, promote female flower bud differentiation in J. sigillata. This study provides a theoretical basis for understanding the relationship between polyamines and female flower bud differentiation in J. sigillata.