Conifer WOX-related homeodomain transcription factors, developmental consideration and expression dynamic of WOX2 during Picea abies somatic embryogenesis

Abstract

In angiosperms, the WOX family of transcription factors has important functions in meristem regulation and in control of the partitioning of developing embryos into functional domains. In this study, a putative WOX2 homologous gene was isolated from Picea abies, and its expression pattern during somatic embryo development was followed using real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). We used strategies of both absolute and relative quantification of gene expression, and benefits and disadvantages of the two methods are presented and discussed. During embryogenesis, PaWOX2 expression was highest at the earliest stages of development, but low levels were also detected in seedling tissues. No PaWOX2 expression was detected in a non-embryogenic cell culture, indicating that PaWOX2 plays a fundamental role during early somatic embryo development, and can be used as a possible marker for embryogenic potential. Additional results show that conifers, like angiosperms, contain a large number of WOX-related genes, many of them expressed during embryo development. In phylogenetic analysis based on the deduced homeodomain of retrieved pine and spruce EST sequences, no conifer WUS homolog was found. Neither did we find any homeodomain to cluster with WOX5. Interestingly, a clade including only conifer sequences derived from various tissues was resolved as sister to a Physcomitrella WOX-like gene, suggestive of the early origin of this gene family. Our results thus provide basic information for further studies of the evolution of this gene family and of their function in relation to meristem dynamics and specification of stem cells in gymnosperms.

WOX2and polar auxin transport during spruce embryo pattern formation

“…in NPA-treated (1 μM) precotyledonary and mature embryos, both comparable in developmental stages to the stage 1-2 and stage 4 embryos, respectively, that we previously used in PaWOX2 analysis, 1 we found that PaWOX2 was significantly upregulated in NPA-treated precotyledonary embryos (2.9-fold) compared to untreated embryos while we could see no significant difference in expression between NPA-treated and untreated mature embryos (Fig. 1).…”

“…Recent analysis by us of WOX-related genes in Picea and Pinus suggests that they play fundamental roles during embryo development also in conifers. 1 It has been proposed that there is a connection between the spatial separation of WOX2 and WOX8, and PAT in the formation of the apical-basal axis in Arabidopsis embryos and that both are involved in the regulation of the auxin efflux carrier PIN1. Auxin also seems to play a crucial role in apical-basal axis formation in conifer embryos based on studies using the polar auxin inhibitor NPA.…”

Somatic Embryogenesis for More Effective Breeding and Deployment of Improved Varieties in Pinus spp.: Bottlenecks and Recent Advances

“…Transcript expression profiling in P. radiata shoot-derived calli and ze-derived EMs showed correlation of WOX2 and ABI3 expression with embryogenic potential whereas LEC1 was expressed in both EM and non-embryogenic calli (Garcia-Mendiguren et al 2015). This is consistent with previous studies conducted in other conifer species (Palovaara and Hakman 2008;Klimaszewska et al 2011), including P. contorta where PcWOX2 was expressed in EM from immature ze and EM-like tissues derived from mature trees but not in non-embryogenic calli derived from a seedling needle (Park et al 2010). Also, ABI3/VP1 appeared to be expressed at low levels during EM proliferation in several conifer species including P. sylvestris (Uddenberg et al 2011).…”

Recent progress in the understanding of tissue culture-induced genome level changes in plants and potential applications

“…Wuschel, a related protein Wuschel homeobox (WOX) (Palovaara and Hakman 2008;Park et al 2010;Gambino et al 2011), MADS domain containing protein Agamouslike15 (AGL15) (Harding et al 2003), Leafy Cotyledon 1 (LEC1) , Leafy Cotyledon 2 (LEC2) (Ledwoń and Gaj 2009), Fusca3 (FUS3), ABA Insensitive 3 (ABI3)/Viviparous1 (VP1) (Su et al 2009), Leafy Cotyledon 1 like (LIL) (Alemanno et al 2008;Schellenbaum et al 2008a;Chiappetta et al 2009) are some of the transcription factors believed to play a crucial role in somatic Plant Cell Rep (2012) 31:597-620 601 embryogenesis. Mutants of the Leafy Cotyledon genes (LEC1, LEC2 and FUS3) displayed drastically reduced somatic embryo production in vitro, thereby proving their key role in in vitro embryogenic response, despite a normal auxin gradient (Gaj et al 2005).…”