MsDUF3700 regulates plant growth via SLY1-mediated DELLA degradation in alfalfa and Arabidopsis

Alfalfa (Medicago sativa L.) is a globally cultivated leguminous forage crop, where plant height constitutes a critical determinant of biomass yield. In the study, we identified a gene encoding a Domain of Unknown Function (DUF)-containing protein, designated MsDUF3700. Transgenic alfalfa overexpressing MsDUF3700 exhibited significant increases in plant height, stem diameter, and above-ground biomass. To delineate the underlying molecular mechanism, we performed yeast two-hybrid screening and identified MsSLEEPY1 (MsSLY1), an F-box protein, as a putative interacting partner of MsDUF3700. The interaction between MsDUF3700 and MsSLY1 was subsequently confirmed by multiple in vitro and in planta assays. We further characterized the function of MsSLY1 in Arabidopsis thaliana, demonstrating that ectopic expression of MsSLY1 rescued the characteristic growth defects of the sly1 mutant, including impaired cotyledon expansion and reduced shoot elongation. Biochemical analyses, including cell-free degradation assays and transient expression experiments in Nicotiana benthamiana, revealed that the MsDUF3700-MsSLY1 complex promotes DELLA protein degradation via the ubiquitin-proteasome pathway, thereby modulating GA signaling. Consistent with this mechanism, genetic analysis showed that overexpression of MsDUF3700 in the sly1 mutant background partially alleviated the dwarf phenotype, supporting a SLY1-dependent role of MsDUF3700 in regulating plant growth. Taken together, these findings uncover a novel function for MsDUF3700 in mediating stem elongation through the MsSLY1-DELLA regulatory module. This study advances our understanding of the genetic and molecular mechanisms governing shoot development in leguminous species and identifies MsDUF3700 as a promising candidate for improving plant architecture and forage yield in alfalfa.