Abstract
Proper embryo development is crucial as that is when the primary body axes are established. In Arabidopsis, AtWOX8 and AtWOX9, members of the Wuschel-related homeobox (WOX) gene family, are critical for embryo development. In Norway spruce, PaWOX8/9, which is expressed in embryos, is the homologue of AtWOX8 and AtWOX9. In this work, it is shown that the transcript abundance of PaWOX8/9 is high during early and late embryogeny and that it decreases when the maturation phase starts. To address the function of PaWOX8/9 during embryo development, RNAi lines were established to down-regulate the transcript level of PaWOX8/9, using both constitutive and inducible promoters. Embryos in the PaWOX8/9 RNAi lines show an aberrant morphology caused by disturbed orientation of the cell division plane at the basal part of the embryonal mass during early and late embryogeny. In addition, the transcript level of several key cell-cycle-regulating genes, for example, PaE2FAB-like and PaCYCLIN B-like, are affected in the PaWOX8/9 RNAi lines. Taken together, our results suggest that PaWOX8/9 may perform an evolutionarily conserved function as a regulator of the establishment of the apical-basal embryo pattern.
Highlights
In seed plants, the embryo displays the basic body polarities and develops along the apical–basal axis to establish two meristems responsible for post-embryonic growth (Ueda and Laux, 2012)
To address the function of PaWOX8/9 during embryo development, RNA interference (RNAi) lines were established to down-regulate the transcript level of PaWOX8/9, using both constitutive and inducible promoters
To address whether PaWOX8/9 activity is important for pattern formation during embryo development in Norway spruce, embryogenic RNAi lines were established to down-regulate the transcript level of PaWOX8/9 using both constitutive and inducible promoters
Summary
The embryo displays the basic body polarities and develops along the apical–basal axis to establish two meristems responsible for post-embryonic growth (Ueda and Laux, 2012). The process that establishes this primary body plan is called embryonic pattern formation. It requires highly regulated spatio-temporal cell division to set up the organ plan and, eventually, the overall shape of the embryo (Berleth and Jurgens, 1993; Traas et al, 1995; Laux et al, 1996). Knowledge about embryonic pattern formation in plants has, to a large extent, been derived from studies of embryo-defective mutants in the angiosperm model species Arabidopsis (Arabidopsis thaliana) (Capron et al, 2009; Kanei et al, 2012). The process of somatic embryogenesis has proved to be a valuable tool for studying the regulation of embryo development in conifers. Somatic embryos have been used for studying gene expression and functions (Tahir et al, 2006; Larsson et al, 2012a, b)
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