Signaling in Early Maize Kernel Development Nicolas M. Doll, Nathalie Depège-Fargeix, Peter M. Rogowsky, Thomas Widiez  Molecular Plant  Volume 10, Issue 3, Pages 375-388 (March 2017) DOI: 10.1016/j.molp.2017.01.008 Copyright © 2017 The Author Terms and Conditions

Figure 1 Early Developmental Stages of Maize Seed and Hormonal Responses. Auxin (violet stars) and cytokinin (CK) (green stars) responses are based on DR5 and TCSv2 promoter activity, respectively; from Chen et al., 2014. (A) ∼3 DAP whole maize kernel. Both auxin and CK responses are found in the endosperm coenocyte, and CK responses are also detected in the placento-chalazal region. (B, D) 6–8 DAP whole maize kernel (B) and zoom on the embryo (D), which is between the late pro-embryo stage and the early transition stage. Auxin response is restricted to the adaxial part of the endosperm, whereas the CK response is found in the whole endosperm but concentrated in the BETL and in the adaxial tip of the endosperm. Arrows in (D) represent putative auxin fluxes from the endosperm to the embryo tip and from the embryo protoderm toward the embryo tip (adapted from Forestan et al., 2010; Chen et al., 2014). (C, E) 8–10 DAP whole maize kernel (C) and zoom on the embryo (E), which is between the late transition stage and the early coleoptilar stage. Auxin responses remain in the adaxial part of the endosperm and surround the embryo with the exception of the suspensor, which is protected by the ESR. CK responses are restricted to the BETL and to the adaxial tip of the endosperm. Arrows in (E) indicate an apical-basal flow from the embryo tip to the meristematic regions. Auxin and CK responses in the embryo are marked by violet and green cells, respectively, in (D) and (E). AL, aleurone layer; BETL, basal endosperm transfer layer; emb, embryo; end, endosperm; ep, embryo proper; ESR, embryo-surrounding region; nuc, nucellus; pc, placento-chalazal cells; per, pericarp; scu, scutellum; SE, starchy endosperm; su, suspensor. Molecular Plant 2017 10, 375-388DOI: (10.1016/j.molp.2017.01.008) Copyright © 2017 The Author Terms and Conditions

Figure 2 BETL Differentiation as an Illustration of Integration of Different Signaling Pathways. Undifferentiated cells of the outer endosperm cell layer, which are in contact with the maternal placento-chalazal region, differentiate into BETL (basal endosperm transfer layer) cells, specialized in nutrient transport from the mother plant to the endosperm. Both the MEG1 small signaling peptide and the MRP-1 transcription factor have been shown to be sufficient to induce BETL cell fate, which also requires sugar and auxin signaling. BETL1, basal endosperm transfer layer 1, MEG1, small peptide Maternally Expressed Gene 1; MN1, cell wall invertase MINIATURE1; MRP-1, TF Myb-Related Protein-1; S4, hexose transporter SWEET4c; YUC1, Yucca1. Molecular Plant 2017 10, 375-388DOI: (10.1016/j.molp.2017.01.008) Copyright © 2017 The Author Terms and Conditions

Figure 3 Expression Pattern of Key Selected Genes in Maize Kernel. For each gene, spatial and temporal gene expression patterns are reported. The absolute expression in the different seed compartments is indicated by a color scale from a transcriptomics analysis carried out by Zhan et al., 2015 on 8 DAP micro-dissected kernels. The graph below represents relative expression at different developmental stages in the whole kernel, adapted from transcriptomics data from Li et al., 2014a. AL, aleurone layer; BETL, basal endosperm transfer layer; CSE, central starchy endosperm; CZ, conductive zone; Emb, embryo; ESR, embryo surrounding region; NA, not available; Nu, nucellus; PC, placento-chalazal cells; Ped, pedicel; Per, pericarp. Molecular Plant 2017 10, 375-388DOI: (10.1016/j.molp.2017.01.008) Copyright © 2017 The Author Terms and Conditions