The ER network, peroxisomes and actin cytoskeleton exhibit dramatic alterations during somatic embryogenesis of cultured citrus cells

Somatic embryogenesis (SE) is an effective approach for citrus genetic improvement, overcoming some of the obstacles presented in conventional breeding. It is known that the remodeling of endomembrane structures and cytoskeleton are essential for plant growth and reproduction, but their behaviors and functions in citrus SE has not been studied. In order to investigate the behaviors of various subcellular structures during this process, we used fluorescent proteins to label multiple endomembrane structures and cytoskeletal network in citrus callus. Confocal microscopy studies indicated that the morphology of endoplasmic reticulum and the numbers of peroxisomes changed significantly after the initiation of embryogenesis. On the other hand, the arrangement of actin filaments also exhibits significant differences in callus maintaining high embryogenic potential, in contrast to callus that are recalcitrant in forming embryos. The treatment of actin depolymerizing drug latrunculin B significantly reduced the number of somatic embryos, indicating that actin filaments play an important role in regulating SE in citrus. In summary, our results suggested that organelle biogenesis, morphogenesis and the dynamic rearrangement of cytoskeleton are crucial in SE of citrus.