Expression of a gymnosperm PIN homologous gene correlates with auxin immunolocalization pattern at cotyledon formation and in demarcation of the procambium during Picea abies somatic embryo development and in seedling tissues

Abstract

In seed plants, the body organization is established during embryogenesis and is uniform across gymnosperms and angiosperms, despite differences during early embryogeny. Evidence from angiosperms implicates the plant hormone auxin and its polar transport, mainly established by the PIN family of auxin efflux transporters, in the patterning of embryos. Here, PaPIN1 from Norway spruce (Picea abies [L.] Karst.), a gene widely expressed in conifer tissues and organs, was characterized and its expression and localization patterns were determined with reverse transcription polymerase chain reaction and in situ hybridization during somatic embryo development and in seedlings. PaPIN1 shares the predicted structure of other PIN proteins, but its central hydrophilic loop is longer than most PINs. In phylogenetic analyses, PaPIN1 clusters with Arabidopsis thaliana (L.) Heynh. PIN3, PIN4 and PIN7, but its expression pattern also suggests similarity to PIN1. The PaPIN1 expression signal was high in the protoderm of pre-cotyledonary embryos, but not if embryos were pre-treated with the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). This, together with a high auxin immunolocalization signal in this cell layer, suggests a role of PaPIN1 during cotyledon formation. At later stages, high PaPIN1 expression was observed in differentiating procambium, running from the tip of incipient cotyledons down through the embryo axis and to the root apical meristem (RAM), although the mode of RAM specification in conifer embryos differs from that of most angiosperms. Also, the PaPIN1 in situ signal was high in seedling root tips including root cap columella cells. The results thus suggest that PaPIN1 provides an ancient function associated with auxin transport and embryo pattern formation prior to the separation of angiosperms and gymnosperms, in spite of some morphological differences.

The role of auxins in somatic embryogenesis of Abies alba

“…Auxin and its polar transport are believed to be mainly established by the PIN family of proteins in Picea abies (Norway spruce) somatic embryos [37]. The expression of the auxin efflux transporter PIN1 had been observed in differentiating procambium, running from the tips of cotyledons down throughout the somatic embryo axis and to the root apical meristem of Picea abies [38]. The centrality of polar auxin transport for the correct patterning of both apical and basal parts of spruce embryos throughout the whole developmental process has been demonstrated by Larsson et al [39] using naphthylphthalamic acid (NPA) treatments.…”

Diversity of phyllotaxis in land plants in reference to the shoot apical meristem structure

“…Furthermore, in light of the fact that similar developmental impairments have been shown in some monocots [113][114][115][116][117] and that homologs of PIN genes have been identified in gymnosperms [118,119], it is generally thought that the auxin mechanism of phyllotaxis regulation may be universal throughout the seed plants. Sequencing analyses have suggested that PIN genes may be present in the seedless land plants as well [119], and PAT has been shown to be present in Physcomitrella [120] and Selaginella [121], indicating that the auxin mechanism of phyllotaxis formation may be common to all land-plant lineages.…”

A quantitative study of cotyledon positioning in conifer development

“…Homologs for a number of the molecules involved in Arabidopsis PAT have been found in recent years in conifer embryos (spruce, Picea abies; Larsson et al 2008Larsson et al , 2012aLarsson et al , 2012bHakman et al 2009;Palovaraa et al 2010aPalovaraa et al , 2010b. These indicate that PAT patterning could be present in conifer development, with similar molecular components to Arabidopsis.…”