Identification of molecular processes that differ among Scots pine somatic embryogenic cell lines leading to the development of normal or abnormal cotyledonary embryos

Abstract

Several coniferous species can today be propagated through somatic embryogenesis, but for species belonging to the Pinus genus, there are still problems related to the small number of genotypes from which embryogenic cultures can be established and the low yield of high-quality cotyledonary embryos. In order to pinpoint molecular processes that might be disturbed during somatic embryogenesis in Scots pine, we have analyzed the expression pattern of selected transcripts during development of somatic embryos in a normal and an abnormal cell line of Scots pine. The selected transcripts have been previously shown to be differentially expressed during early zygotic embryogenesis in Scots pine (Merino et al. 2016). Based on the transcripts that accumulated differentially between the two cell lines, we conclude that the apical-basal polarization in early somatic embryos and the transition from the morphogenic phase to the maturation phase are disturbed in the abnormal cell line. A comparison between transcript accumulation during somatic and zygotic embryogenesis highlighted problems with the continuous embryo degeneration processes in embryogenic cultures of Scots pine. Transcripts that were highly abundant during the cleavage process in zygotic embryos showed different accumulation patterns during somatic embryogenesis in Scots pine compared to those in Norway spruce. Furthermore, altering the expression of these transcripts in embryogenic cultures of Norway spruce resulted in a changed proliferation pattern of the embryos so that they became more similar to proliferating somatic embryos of Scots pine. Taken together, our results provide a deeper understanding of the deviations in abnormal cell lines and indicate that embryogenic cultures of Scots pine are proliferating by a cleavage-like process.

New Approaches to Optimize Somatic Embryogenesis in Maritime Pine

“…Maritime pine WOX gene family has been studied recently (Alvarez et al, 2018) and WOX2 expression has been shown to be highest at early embryogenic stages and decreased along the maturation process being lower in mature somatic embryos which agree with our WOX2 expression profile sampled at 0, 7, and 12 weeks in SK lines. Similar results were obtained in other conifers as Pinus sylvestris (Merino et al, 2018), Picea (Palovaara and Hakman, 2008; Klimaszewska et al, 2011), Larix decidua (Rupps et al, 2016), Pinus contorta (Park et al, 2010), and Chinese fir (Zhou et al, 2017).…”

“…Results presented here show a decrease in the expression of both WOX2 and LEC1 genes along the maturation phase but only on P. pinaster SK lines with maturation capacity (Figure 6). Interestingly, Merino et al (2018) did not find significant differences in WOX2 expression patterns of two scots pine embryogenic lines that differed in their ability to produce normal embryos. Those differences were, on the contrary, detected for the patterns of transcripts accumulation on a LEC1 -type HAP3 gene.…”

Effect of Thermal Stress on Tissue Ultrastructure and Metabolite Profiles During Initiation of Radiata Pine Somatic Embryogenesis

“…This supernumerary suspensor cell scenario may be caused by a disturbed polar auxin transport, which stimulates division of ECs adjacent to the tube-like cells, as described by Abrahamsson et al (2012). Similar morphologies were described by Merino et al (2018) for Norway spruce early somatic embryos leading to abnormal somatic embryos. These authors pointed out that there is a strong relationship among early somatic embryo morphology, its capacity to develop into a mature embryo and the expression of certain transcripts.…”

Pinus spp. Somatic Embryo Conversion under High Temperature: Effect on the Morphological and Physiological Characteristics of Plantlets

“…In our experiments we observed that, in both species, embryos were formed with normal and abnormal morphologies. Merino et al [35] in Scots pine attributed the formation of ses with normal and abnormal morphology to the difference of transcripts in embryogenic cells. However, the increase in temperature did not significantly promote the formation of abnormal embryos.…”