Tissue Specific Control of the Maize (Zea mays L.) Embryo, Cortical Parenchyma, and Stele Proteomes by RUM1 Which Regulates Seminal and Lateral Root Initiation

The different root types of maize (Zea mays L.) originate from distinct tissues during development. The maize mutant rum1 (rootless with undetectable meristems 1) does not initiate seminal roots and lateral roots in the primary root. While seminal roots are laid down during embryogenesis, endodermis cells of the parenchyma, and pericycle cells of the stele contribute to the postembryonic initiation of lateral roots. In this study, tissue specific protein profiles of immature embryo, cortical parenchyma which includes endodermis, cortex and epidermis cell layers, and stele tissues were compared between wild-type and rum1 via 2-DE. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) identified 86 proteins encoded by 69 genes that were differentially accumulated between wild-type and rum1 (Fc 2: 2; FDR < 10%) demonstrating that RUM1 affects the proteome composition of cortical parenchyma, stele and embryo tissues. While several protein isoforms, protein families or members of biochemical pathways regulated by RUM1 were differentially accumulated in at least two tissues, other proteins displayed tissue specific expression differences. Multiple members of the globulin gene family displayed, for example, embryo specific expression differences, while different glycolysis related enzymes were differentially expressed in all three analyzed tissues. Proteins related to signal transduction and cell fate were overrepresented in cortical parenchyma versus embryo and embryo versus stele tissues, respectively, and might imply tissue specific functions of these protein classes.