Pilosella: A Dicotyledonous Model for Studying Aposporous, Autonomous Apomixis

Pilosella, a member of the Compositae, is a model system used to study the molecular genetics of aposporous apomixis. These plants are small, rapidly growing perennials that are easy to cultivate both in the greenhouse and in tissue culture. Apomixis in Pilosella occurs by apospory where mitotically derived embryo sacs arise adjacent to cells undergoing female gamete meiosis in the ovule. Seed initiation is autonomous, where both embryo and endosperm form without fertilization in the aposporous embryo sac. Apomixis is not fully penetrant in Pilosella. Instead, plants are facultatively apomictic, and apomixis can be easily scored through the simple decapitation of the immature capitulum bud. Natural sexual and facultatively apomictic forms are readily cross-compatible, facilitating comparative studies of inheritance and allele function. A wide range of experimental methods have been described for these plants, including histological techniques for studying the cytological aspects of apomixis, an efficient Agrobacterium-mediated transformation system, CRISPR/Cas9 mutagenesis, and mapping approaches that use deletion mutation and segregation in polyhaploid populations. Freely available online resources include a genome assembly, a molecular map based on cDNA markers and a transcriptome database. Collectively, these resources make Pilosella a highly tractable experimental system for studying the genetic control of native apomixis.