Mitogen-activated protein kinases concentrate in the vicinity of chromosomes and may regulate directly cellular patterning in Vicia faba embryos

Mitogen-activated protein kinases seem to mark genes which are set up to be activated in daughter cells and thus they may play a direct role in cellular patterning during embryogenesis. Embryonic patterning starts very early and after the first division of zygote different genes are expressed in apical and basal cells. However, there is an ongoing debate about the way these different transcription patterns are established during embryogenesis. The presented data indicate that mitogen-activated protein kinases (MAPKs) concentrate in the vicinity of chromosomes and form visible foci there. Cells in the apical and basal regions differ in number of foci observed during the metaphase which suggests that cellular patterning may be determined by activation of diverse MAPK-dependent genes. Different number of foci in each group of separating chromatids and the specified direction of these mitoses in apical-basal axis indicate that the unilateral auxin accumulation in a single cell may regulate the number of foci in each group of chromatids. Thus, we put forward a hypothesis that MAPKs localized in the vicinity of chromosomes during mitosis mark those genes which are set up to be activated in daughter cells after division. It implies that the chromosomal localization of MAPKs may be one of the mechanisms involved in establishment of cellular patterns in some plant species.

Mitogen-activated protein kinases participate in determination of apical-basal symmetry in Pisum sativum

Mitogen-activated protein kinases (MAPKs) are implicated in various processes in plants. Apart from response to biotic and abiotic stresses they are involved in regulation of embryo development. Although MAPKs were found to be indispensable during embryo development it has never been established at which stages of embryogenesis and in which regions of a plant embryo activated MAPKs can be observed. Here, we show that apical and basal regions display activation of the same types of MAPKs and the only difference concerns the level of their phosphorylation and cellular localization. Dually-phosphorylated MAPKs were found in nuclei of the apical region of an embryo both at the early and late cotyledonary stage while no immunofluorescence signals were detected in nuclei of the basal region. However, in this case phosphorylated MAPKs were immunodetected in cytoplasm in the apical domain of cortex cells, indicating their role in auxin transport from the basal to apical region of an embryo. Furthermore, obtained data indicate that nuclear localization of activated MAPKs may result from epigenetic modifications and polar auxin transport. The presented data and previous studies lead to the conclusion that activated MAPKs and their cellular localization define apical and basal regions during formation of an apical-basal axis.

Auxin Biosynthesis, Accumulation, Action and Transport are Involved in Stress-Induced Microspore Embryogenesis Initiation and Progression in Brassica napus

Isolated microspores are reprogrammed in vitro by stress, becoming totipotent cells and producing embryos and plants via a process known as microspore embryogenesis. Despite the abundance of data on auxin involvement in plant development and embryogenesis, no data are available regarding the dynamics of auxin concentration, cellular localization and the expression of biosynthesis genes during microspore embryogenesis. This work involved the analysis of auxin concentration and cellular accumulation; expression of TAA1 and NIT2 encoding enzymes of two auxin biosynthetic pathways; expression of the PIN1-like efflux carrier; and the effects of inhibition of auxin transport and action by N-1-naphthylphthalamic acid (NPA) and α-(p-chlorophenoxy) isobutyric acid (PCIB) during Brassica napus microspore embryogenesis. The results indicated de novo auxin synthesis after stress-induced microspore reprogramming and embryogenesis initiation, accompanying the first cell divisions. The progressive increase of auxin concentration during progression of embryogenesis correlated with the expression patterns of TAA1 and NIT2 genes of auxin biosynthetic pathways. Auxin was evenly distributed in early embryos, whereas in heart/torpedo embryos auxin was accumulated in apical and basal embryo regions. Auxin efflux carrier PIN1-like gene expression was induced in early multicellular embryos and increased at the globular/torpedo embryo stages. Inhibition of polar auxin transport (PAT) and action, by NPA and PCIB, impaired embryo development, indicating that PAT and auxin action are required for microspore embryo progression. NPA also modified auxin embryo accumulation patterns. These findings indicate that endogenous auxin biosynthesis, action and polar transport are required in stress-induced microspore reprogramming, embryogenesis initiation and progression.