Female gametophyte development, pollen‒pistil interactions and embryogenic patterns in chicory (Cichorium intybus): a self-incompatibility perspective

Key message: Cytological and molecular investigations in chicory revealed crucial aspects related to female gametophyte development, pollen‒stigma interactions, and self-incompatibility responses. Abstract: The Asteraceae family, one of the largest of angiosperms, comprises approximately 24,000 species and exhibits considerable variation in reproductive biology. Cichorium intybus (commonly known as chicory) is among the most well-known and widespread species of the family. In addition to its economic and commercial value, chicory is considered one of the most interesting species in its family for the study of sporophytic self-incompatibility (SSI). Information regarding megasporogenesis, megagametogenesis, pollen tube development, and embryogenesis in this species is almost entirely absent in the scientific literature. Using confocal laser scanning microscopy (CLSM), we conducted a detailed investigation of female gametophyte development, providing a comprehensive characterization of the cytological stages involved in megasporogenesis and megagametogenesis. To investigate the dynamics and timing of pollen tube development and pollen rejection, we microscopically examined the interactions between pollen and stigmas in both cross- and self-pollinated plants. The response was similar to those documented in other Asteraceae species with a 'semidry' type of stigma. Integrated RNA-seq analyses further highlighted transcriptional changes during self- and non-self-pollen recognition and led to the identification of potential candidate genes involved in pollen tube development and callose deposition (in the case of self-incompatibility reactions). In parallel, for the first time, we characterized both the embryogenesis process and embryo sac degeneration in a compatible and incompatible crosses, respectively.