The dicotyledonous genus Hieracium contains apomictic and sexual species, and is used as a model to study apomixis at the molecular level. Apomixis is facultative and occurs by apospory followed by autonomous embryo and endosperm formation. The sexual pathway initiates first, then apomixis begins with the differentiation of initial cells, and in the more successful apomicts the apomictic pathway displaces the sexual. Genetic analysis showed that apomictic seed set is dependent on the activity of a dominant locus and also modifiers that can influence the fate of initial cell development. The initiation of apomixis is presaged by the altered expression of a DEFICIENS homologue. Initiation of apomixis is not related to alterations in callose deposition or ß-l,3-glucanase activity as has been proposed in other apomicts. Ablation of ovule tissues showed that the funiculus or substances flowing through it exert a negative effect on aposporous initial cell formation. Initial cells were capable of forming embryo sacs, embryos and endosperm in the altered context of ovule development resulting from funicular cell ablation. Signals from surrounding ovule tissues might therefore play a role in directing initial cell fate and the progression of apomixis. We propose that the apomixis locus confers the potential for the components of apospory and autonomous embryo and endosperm development, while other genes that normally regulate ovule and seed maturation may act as modifiers. The combination of locus and modifier activity results in a particular mode of apomixis. The locus and the modifiers require characterization to effectively manipulate apomixis in crops where this beneficial trait is largely absent.
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.