Mps-one-binder (Mob) proteins play an important role in chromosome separation and cell plate formation in yeast. We cloned two Mob 1-like genes from alfalfa (Medicago sativa L.) and show that one gene is constitutively expressed while the other is expressed only in flower buds during sporogenesis and gametogenesis. For the analysis of gene expression during reproduction in alfalfa wild-types and apomeiotic mutants, a specific antisense riboprobe was designed for MsMob 1 transcripts and a polyclonal antibody was raised against MsMob 1 proteins. In situ mRNA localization as well as protein immunolocalization proved that MsMob1-like genes are specifically expressed in degenerating megaspores of normal ovules and in enlarged megaspore mother cells and embryo sacs of apomeiotic ovules. Gene products were also found in microspore tetrads at the beginning of pollen development as well as in tapetum cells of anthers undergoing programmed cell death to allow pollen dispersal at maturity. Overall results suggest that MsMob 1-like genes can play a key role during the reproductive pathway in plants.