The role of actin isoforms in somatic embryogenesis in Norway spruce

Abstract

BackgroundSomatic embryogenesis in spruce is a process of high importance for biotechnology, yet it comprises of orchestrated series of events whose cellular and molecular details are not well understood. In this study, we examined the role of actin cytoskeleton during somatic embryogenesis in Norway spruce line AFO 541 by means of anti-actin drugs.ResultsApplication of low doses (50-100 nM) of latrunculin B (Lat B) during the maturation of somatic embryos predominantly killed suspensor cells while leaving the cells in meristematic centres alive, indicating differential sensitivity of actin in the two cell types. The treatment resulted in faster development of more advanced embryos into mature somatic embryos and elimination of insufficiently developed ones. In searching for the cause of the differential actin sensitivity of the two cell types, we analysed the composition of actin isoforms in the culture and isolated four spruce actin genes. Analysis of their expression during embryo maturation revealed that one actin isoform was expressed constitutively in both cell types, whereas three actin isoforms were expressed predominantly in suspensor cells and their expression declined during the maturation. The expression decline was greatly enhanced by Lat B treatment. Sequence analysis revealed amino-acid substitutions in the Lat B-binding site in one of the suspensor-specific actin isoforms, which may result in a different binding affinity for Lat B.ConclusionsWe show that manipulating actin in specific cell types in somatic embryos using Lat B treatment accelerated and even synchronized the development of somatic embryos and may be of practical use in biotechnology.

Organisation and regulation of the cytoskeleton in plant programmed cell death

“…In anisotropically expanding embryonal tube cells, the microtubules form a transverse cortical array and microfilaments are oriented longitudinally. 12,13 In the suspensor cells microtubules fragment and disassemble, but tubulin levels remain stable 12 whereas longitudinal microfilaments bundle and form long cables, which disappear at the onset of DNA fragmentation (Figures 1a and b; Table 1). The reorganisation of F-actin in the suspensor cells is accompanied by upregulation of three actin genes.…”

“…The reorganisation of F-actin in the suspensor cells is accompanied by upregulation of three actin genes. 13 Senescence is important for plant organ replacement due to aging (e.g. leaves) or following the completion of the organ function (e.g.…”

“…F-actin bundling may regulate the pace of PCD, as treatment with the actindepolymerising drug, bistheonellide, speeds up PCD suspensor. 12,13 This suggests that actin polymerisation is important for initiating or mediating relatively slow vacuolar PCD in the embryo suspensor. In contrast, treatment of differentiating tracheary elements with cytochalasin B has no effect on PCD, but perturbs differentiation.…”

“…The first is characterised by the formation of bundled actin cables, and has been reported in several examples of HR and developmental PCD. 12,13,40,41,[60][61][62] This is likely to involve reduced activity of severing and barbed end capping proteins, and activity of bundling proteins (Figure 3a), though no candidates have been identified in these systems yet. In the second scenario, observed in the SI response, F-actin initially undergoes depolymerisation, followed by the formation of actin foci.…”

Focus on ADF/Cofilin: Beyond Actin Cytoskeletal Regulation

“…After gastrula, the developments of ectoderm, mesoderm, and endoderm are initiated by rapid cell division. Actin cytoskeletal organization is involved in cell divisions for determining the cell polarity, orientation, and proliferation in embryos, as well as the development of cell walls in higher plants [56,57]. Deactivation of ADF/cofilin is critical for the compaction stage, which is a process in 8-cell stage of embryos [58].…”