Résumé
Paspalum notatum, a subtropical forage grass native to South America, has proven to be a fruitful model for studying apomixis in plants. Several genes associated with apomixis have been identified through geneticmapping and comparative mRNA analyses, including QUI-GON JINN (QGJ) encoding a MAPK3 protein of the YODA family. Interestingly, the downregulation of QGJ in P. notatum apomictic genotypes has been associatedwith a decrease in the number of unreduced (aposporous) embryo sacs. To disclose QGJ function during sexual development, we have undertaken its functional characterization in the model plant Arabidopsis thaliana usinggenetic and cellular approaches. The protein accumulation generated by GUS reporter lines indicated that QGJ is expressed during ovule development and accumulates in the L1 cell layer of the ovule primordium, but notin the placenta. QGJ is also expressed in degenerating megaspores, while functional megaspores completely lack signal. Finally, in developing seeds, the endosperm showed GUS accumulation, but the zygote and growingembryos were completely devoid of signal. Furthermore, qgj defective mutants led to reproductive alterations of the female development, in a manner reminiscent of apomixis. Furthermore, qgj mutants showed alterationsduring female meiosis, female gametophytic development and early seed development. These results indicate that QGJ is expressed during megasporogenesis and endosperm development, and suggest that its functionis related with megaspore degeneration in the tetrad, gametophyte development and non-cell autonomous control of embryo development.