Following Vegetative to Embryonic Cellular Changes in Leaves of Arabidopsis Overexpressing LEAFY COTYLEDON2

Abstract

Embryogenesis in flowering plants is controlled by a complex interplay of genetic, biochemical, and physiological regulators. LEAFY COTYLEDON2 (LEC2) is among a small number of key transcriptional regulators that are known to play important roles in controlling major events during the maturation stage of embryogenesis, notably, the synthesis and accumulation of storage reserves. LEC2 overexpression causes vegetative tissues to change their developmental fate to an embryonic state; however, little information exists about the cellular changes that take place. We show that LEC2 alters leaf morphology and anatomy and causes embryogenic structures to form subcellularly in leaves of Arabidopsis (Arabidopsis thaliana). Chloroplasts accumulate more starch, the cytoplasm fills with oil bodies, and lytic vacuoles (LVs) appear smaller in size and accumulate protein deposits. Because LEC2 is responsible for activating the synthesis of seed storage proteins (SSPs) during seed development, SSP accumulation was investigated in leaves. The major Arabidopsis SSP families were shown to accumulate within small leaf vacuoles. By exploiting the developmental and tissue-specific localization of two tonoplast intrinsic protein isoforms, the small leaf vacuoles were identified as protein storage vacuoles (PSVs). Confocal analyses of leaf vacuoles expressing fluorescently labeled tonoplast intrinsic protein isoforms reveal an altered tonoplast morphology resembling an amalgamation of a LV and PSV. Results suggest that as the LV transitions to a PSV, the tonoplast remodels before the large vacuole lumen is replaced by smaller PSVs. Finally, using vegetative and seed markers to monitor the transition, we show that LEC2 induces a reprogramming of leaf development.

Spatio‐temporal patterning of arginyl‐tRNA protein transferase (ATE) contributes to gametophytic development in a moss

“…However, overexpression of SnRK1 in A. thaliana did not result in enhanced starch accumulation (Jossier et al ., ) which is in agreement with the fact that an increased starch content in A. thaliana seems to be linked to specific conditions, such as hypoxia. Connections between starch accumulation and development are also known for A. thaliana mutants overexpressing the key metabolic regulatory transcription factor LEAFY COTYLEDON2 (LEC2) (Feeney et al ., ). Besides an increased starch accumulation, the overexpression of LEC2 induced accumulation of oil bodies, an effect that was also observed in ate1ate2 plants of A. thaliana (Holman et al ., ) but not in the d|ate moss mutants described here (Fig.…”

Lipid Droplet-Associated Proteins (LDAPs) Are Required for the Dynamic Regulation of Neutral Lipid Compartmentation in Plant Cells

“…LEC2 is a major seed-specific transcription factor that up-regulates many of the genes involved in oil biosynthesis, and ectopic expression of LEC2 in leaves elevates TAG production (Santos Mendoza et al, 2005;Andrianov et al, 2010;Petrie et al, 2010;Kim et al, 2013). The absolute amounts of oleosin transcripts induced in this system, however, are not as high as those observed in developing seeds (Feeney et al, 2013;Kim et al, 2013), and, as such, the level of TAG packaging proteins is likely to be reduced relative to TAG synthesis. Evidence in support of this premise is provided in Figure 7A, which shows that transient expression of Arabidopsis LEC2 in tobacco leaves resulted in the formation of several aberrant, supersized LDs in comparison with the wild type.…”

A transcriptional view on somatic embryogenesis

“…Constitutive overexpression of LEC1 , L1L or LEC2 in arabidopsis appears to induce direct SE, as a callus phase has not been described (Lotan et al., 1998; Mu et al., 2013; Stone et al., 2001). Chemical activation of LEC2 in 7‐day‐old seedlings induced embryo characteristics in leaves, but did not induce SE (Feeney, Frigerio, Cui, & Menassa, 2013), suggesting that seedlings at this developmental stage have already lost their competence for SE. Chemical activation of LEC1 within 48 h after imbibition induced small seedlings that consist of smooth, swollen, somatic embryo‐like tissue, while LEC1 activation just after germination induced embryo‐like tissue only from the primary root meristem, and LEC1 activation 4 d after imbibition had no effect at all (Junker et al., 2012).…”