PFMAGO, a MAGO NASHI-like factor, interacts with the MADS-domain protein MPF2 from Physalis floridana

MADS-domain proteins serve as regulators of plant development and often form dimers and higher order complexes to function. Heterotopic expression of MPF2, a MADS-box gene, in reproductive tissues is a key component in the evolution of the inflated calyx syndrome in Physalis, but RNAi studies demonstrate that MPF2 has also acquired a role in male fertility in Physalis floridana. Using the yeast 2-hybrid system, we have now identified numerous MPF2-interacting MADS-domain proteins from Physalis, including homologs of SOC1, AP1, SEP1, SEP3, AG, and AGL6. Among the many non-MADS-domain proteins recovered was a homolog of MAGO NASHI, a highly conserved RNA-binding protein known to be involved in many developmental processes including germ cell differentiation. Two MAGO genes, termed P. floridana mago nashi1 (PFMAGO1) and PFMAGO2, were isolated from P. floridana. Both copies were found to be coexpressed in leaves, fruits, and, albeit at lower level, also in roots, stems, and flowers. DNA sequence analysis revealed that, although the coding sequences of the 2 genes are highly conserved, they differ substantially in their intron and promoter sequences. Two-hybrid screening of a Physalis expression library with both PFMAGO1 and PFMAGO2 as baits yielded numerous gene products, including an Y14-like protein. Y14 is an RNA-binding protein that forms part of various "gene expression machines." The function of MPF2 and 2 PFMAGO proteins in ensuring male fertility and evolution of calyx development in Physalis is discussed.