PRJNA706142
Transcriptomes in laser microdissection (LMD) captured apomictic cells to delineate nucellar embryogenesis initiation of citrus
Citrus nucellar polyembryony (NPE) is a mode of sporophytic apomixis that allows clonal propagation of rootstocks, but it impedes citrus cross breeding. To dissect the cellular processes involved in nucellar poly-embryony (NPE) in citrus, we compared the transcriptome profiles in LMD-captured citrus apomictic cells and the nucellar sporophytic cells at two nucellar embryogenesis initiation (NEI) stages. At earlier NEI stage (3 d before anthesis), when the sexual embryo sac is undergoing mega-gametogenesis and the NEI cells are not observable under microscope, the 6-7 layers of nucellar tissues (i.e., Poly-NC and Mono-NC) were captured from the ovary sections of the poly- and mono-embryonic F1 progenies of Hirado Buntan pummelo (mono-embryonic) and Fairchild mandarin (poly-embryonic), respectively. At later NEI stage (7 d after anthesis), when the zygote in embryo sac is undergoing mitosis and the densely cytoplasmic NEI cells are observable under microscope, the NEI cells and sporophytic nucellar (SO) cells were captured from the ovary sections of the highly poly-embryonic Ponkan mandarin. In our results, NPE-controlling gene CitRWP and a C2H2 domain-containing transcription factor gene were specifically expressed in apomictic cells. Ribosome biogenesis and protein degradation were activated, whereas auxin polar transport was repressed in apomictic cells. ROS accumulated in the poly-embryonic ovules, and response to oxidative stress was provoked in apomictic cells. The activated embryogenic development and callose deposition processes indicated the embryogenic fate of NEI cells. A working model was proposed to delineate NPE initiation in citrus.