Analysis of the CLE gene family in mulberry (Morus alba L.) and their function under salt stress

CLE peptides, as members of the plant secretory peptide family, play a crucial role in nutrient homeostasis, root growth, floral morphogenesis, meristem maintenance, and responses to abiotic and biotic stresses. Notwithstanding the substantial progress that has been made in comprehending the functions of CLE peptides, very little information is available regarding their responses to salt stress. Mulberry is a notable traditional economic woody plant, demonstrating a remarkable ability to adapt to various adverse conditions, including saline environments. However, the CLE gene family in mulberry has not been extensively studied. In this study, 28 putative MaCLE genes and 34 potential MaCLE receptor genes were identified in mulberry. The organ-specific expression of these 28 putative MaCLE genes was observed in all detected tissues (root, stem, leaf), showing six different expression patterns. The expression levels of the 28 putative MaCLE genes and 34 potential MaCLE receptor genes were detected with diverse expression patterns under salt stress, and some important salt-responsive CLE peptides and receptor were identified. Furthermore, functional analysis indicates that MaCLE2, 9, 10, 13, 16, and 17 negatively regulate salt tolerance in mulberry, albeit through distinct mechanisms. MaCLE2, 16, and 17 suppress lateral root development and reduce ROS scavenging enzyme activity under salt stress, whereas MaCLE13 inhibits both lateral root growth and proline synthesis. In contrast, MaCLE9 functions exclusively by repressing proline synthesis, while MaCLE10 solely restricts lateral root development under salt stress conditions. This study lays a foundation for further investigations into the functions of MaCLE peptides in mulberry trees under salt stress.