Plant β-galactosidases (BGAL) function in various cell wall biogeneses and modifications, and they belong to the glycoside hydrolase family. However, the roles of BGAL family members in Medicago truncatula cell wall remodeling remain unclear. In this study, a total of 25 MtBGAL members of the glycoside hydrolase gene family 35 were identified, and they were clustered into nine sub-families. Many cis-acting elements possibly related to MeJA and abscisic acid responses were identified in the promoter region of the MtBGAL genes. Transcript analyses showed that these MtBGAL genes exhibited distinct expression patterns in various tissues and developing stem internodes. Furthermore, a stem-specific expression module associated with cell wall metabolic pathways was identified by weighted correlation network analysis (WGCNA). In particular, MtBGAL1 and MtBGAL23 within the stem-specific expression module were highly expressed in mature stems. In addition, several genes involved in lignin, cellulose, hemicellulose and pectin pathways were co-expressed with MtBGAL1 and MtBGAL23. It was also found that MtBGAL1 and MtBGAL23 were localized to the cell wall at the subcellular level, indicating their roles in the modification of cell wall metabolites in Medicago. As a whole, these results will be useful for further functional characterization and utilization of BGAL genes in cell wall modifications aiming to improve the quality of legume forage crops.
Keywords: BGAL genes; Medicago truncatula; cell wall remodeling; expression profile; phylogenetic analysis.