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POLYCOMB COMPLEX FUNCTION IN APOMIXIS
Double fertilization is required during sexual reproduction in plants to activate embryo and endosperm formation in the developing seed, except in apomictic species, which form viable seeds asexually without fertilization. In Arabidopsis, a repressive Polycomb-group protein complex blocks seed initiation in the absence of fertilization. Rodrigues et al. (pages 2372–2386) show that one member of the complex has an altered yet essential function in apomictic as well as in fertilization-induced seed initiation in the daisy-like Hieracium. The cover shows a scanning electron micrograph of the Hieracium fruit (achene), which is adapted for wind dispersal. The embryo is found inside the elongated part of the achene. The sample and original image were prepared by Anna Koltunow; the final image was sharpened and color enhanced by Susan Johnson.