Identification of putative homologs of Larix decidua to BABYBOOM (BBM), LEAFY COTYLEDON1 (LEC1), WUSCHEL-related HOMEOBOX2 (WOX2) and SOMATIC EMBRYOGENESIS RECEPTOR-like KINASE (SERK) during somatic embryogenesis

Abstract

Embryogenesis-related genes ( LdBBM, LdLEC1, LdWOX2 and LdSERK ) were confirmed in sequence and expression abundance for Larix decidua —these findings are valid for somatic as well as for zygotic embryo development.S omatic embryogenesis is a reliable source of high-quality genotypes as it presents an advantageous alternative for conifers in forestry, independent from seed production. Although this propagation method is already being applied, molecular factors initiating and controlling the process remain to be understood. The embryogenesis-associated genes BABYBOOM (BBM), LEAFY COTYLEDON1 (LEC1), WUSCHEL-related HOMEOBOX2 (WOX2) and SOMATIC EMBRYOGENESIS RECEPTOR-like KINASE (SERK) were identified and analyzed in somatic embryos of the European larch, L. decidua Mill. Subsequent comparisons with annotated sequences displayed similarities with angiosperm homologs. Transcript accumulation of the identified genes during embryogenesis has been analyzed. LdLEC1 and LdWOX2 are mainly expressed during early embryogenesis, whereas LdBBM and LdSERK reveal increased expression during later development. Temporal and spatial expression studies revealed a specific LdLEC1 signal in the outer cell layer of young embryo heads, whereas mature embryos showed a homogeneous expression. The overexpression of LdLEC1 in Arabidopsis influences germination and cotyledon formation, thus indicating the interspecific importance of LEC1 for proper embryo and specifically cotyledon development. Our data support a conserved role of principal regulators during plant embryogenesis that may be used as molecular markers for embryogenicity and to further determine initiating processes of somatic embryogenesis.

Establishment of a somatic embryo regeneration system and expression analysis of somatic embryogenesis-related genes in Chinese chestnut (Castanea mollissima Blume)

“…5a). CmSERK expression reached a peak in EC stage and then decreased gradually, while increased expression of LdSERK in Larix decidua was observed (Rupps et al 2016). The expression levels of CmSERK were detected in embryogenic and non-embryogenic calli, which was similar to the results reported for L. decidua, Secale cereale, as well as Medicago truncatula (Nolan et al 2003;Gurszczyńska and;Rakoczy-Trojanowska 2011;Rupps et al 2016).…”

“…CmSERK expression reached a peak in EC stage and then decreased gradually, while increased expression of LdSERK in Larix decidua was observed (Rupps et al 2016). The expression levels of CmSERK were detected in embryogenic and non-embryogenic calli, which was similar to the results reported for L. decidua, Secale cereale, as well as Medicago truncatula (Nolan et al 2003;Gurszczyńska and;Rakoczy-Trojanowska 2011;Rupps et al 2016). As a specific marker of embryogenic cells (Schmidt et al 1997), combined with a high expression level at an early stage of this study, we propose that CmSERK plays a crucial role in the initiation of embryogenesis in Chinese chestnut.…”

“…The molecular mechanism of somatic embryogenesis has been extensively investigated (Rupps et al 2016;Orłowska et al 2017). The current results reveal that a number of embryogenesis-related genes have been identified, and some of the genes are essential for somatic embryogenesis, particularly at the initiation stage, such as Somatic Embryogenesis Receptor-like Kinase (SERK; Hecht et al 2001), WUSCHEL (WUS; Wang et al 2009), Leafy Cotyledon (LECs, i.e.…”

“…The current results reveal that a number of embryogenesis-related genes have been identified, and some of the genes are essential for somatic embryogenesis, particularly at the initiation stage, such as Somatic Embryogenesis Receptor-like Kinase (SERK; Hecht et al 2001), WUSCHEL (WUS; Wang et al 2009), Leafy Cotyledon (LECs, i.e. LEC1, LEC2 and FUS3; Gaj et al 2005;Rupps et al 2016) and Agamous-Like15 (AGL15; Karlova et al 2006). The SERK gene, encoding transmembrane kinase, marks the formation of embryogenic cells in culture and may be involved in the somatic embryogenesis signaling pathway by forming a protein complex with AGL15 (Karlova et al 2006;Cai 2011).…”

Coexpression of <i>WUSCHEL related homeobox</i> (<i>WOX</i>) <i>2</i> with <i>WOX8</i> or <i>WOX9</i> promotes regeneration from leaf segments and free cells in <i>Nicotiana tabacum</i> L.

“…These genes play important roles in various developmental events, such as zygote polarization, embryonic tissue proliferation, embryonic pattern formation, stem cell niche maintenance and flower development and lateral organ development (Breuninger et al 2008;Chung et al 2016;Costanzo et al 2014;Ueda and Laux 2012;Wu et al 2007;Zhou et al 2015). The WOX gene family is evolutionarily conserved throughout the plant kingdom (van der Graaff et al 2009), and their orthologs also showed specific expression in zygotic and/or somatic embryogenesis in different species; for example, Vitis vinifera (Gambino et al 2011), Populus tomentosa (Liu et al 2014) and the gymnosperms Larix decidua (Rupps et al 2016) and Picea abies (Hedman et al 2013;Palovaara et al 2010;Zhu et al 2016), suggesting their functional conservation.…”