Fipexide Rapidly Induces Callus Formation in Medicago sativa by Regulating Small Auxin Upregulated RNA (SAUR) Family Genes

The small-molecule compound fipexide (FPX) has been shown to promote callus formation in several plants, but its effects on forage crops remain unexplored, and its molecular mechanism is not yet fully understood. In this study, we evaluated FPX-induced callus formation from seeds for up to four weeks in four elite cultivars of Medicago sativa, finding it to be faster than the classical 2,4-D/6-BA treatment for the first two weeks. Notably, the cellular organization of FPX-induced calli differed from those induced by 2,4-D/6-BA by showing almost no conducting tissues. Comparative transcriptome analysis revealed dynamic gene expression changes during the early and late stages of callus induction, such as multicellular organism development and response to auxin. Interestingly, in both M. sativa and Arabidopsis, FPX regulates a group of small auxin upregulated RNA (SAUR) family genes, which are known to fine-tune growth in response to internal and external signals. This suggests a potential evolutionary conserved molecular mechanism underlying FPX-induced callus formation across plant species.