She began her studies in the realm of plant molecular sciences three years ago at the University of Kaposvár, Hungary. As a research student she was involved in several projects led by Zsolt Pónya PhD, focusing on the cellular/molecular aspects in vitro versus in vivo zygotic embryo formation in angiosperms with special regard to comparing zygote formation and egg activation in the plant versus animal kingdom using micromanipulation techniques. She is co-author of the study by Zsolt Pónya, published in IJMS: “When Isolated a Full Receptivity, in Vitro Fertilized Wheat (Triticum aestivum, L.) Egg Cells Reveal [Ca2+]cyt Oscillation of Intracellular Origin”. She is currently the CEO of a software developing company: eSolution Ltd., Hungary, which deals with data processing and evaluation of results gathered in various research projects and in other versatile areas such as engineering.
Albeit Nawaschin discovered double fertilisation, during which two female reproductive cells are fertilised, well over a hundred years ago (1989), this unique reproduction strategy characteristic of flowering plants has remained elusive and defied attempts to disentangle the molecular and cellular mechanisms that ultimately lead to a life strategy fundamentally different from that of animals. The remarkable feature of this life cycle is the masterly treatment of the alternation of generations between a diploid sporophyte and a haploid gametophyte, the latter allowing for purging the population of deleterious mutations since the phenotype reflects the haploid genotype. Double fertilisation involves a complex series of interactions, a key step of which is the activation of the egg cell produced by the haploid female megagametophyte. The cascade events of the sperm-induced activation of the angiosperm egg and the concomitantly unfolding zygote development coupled with the switch from maternal to embryonic control of gene activation and resulting in asymmetrical cell cleavage that produces two daughter cells of different cell fate still await deciphering owing mainly to the inaccessibility of the female gametes/zygotes of higher plants as these develop deeply enclosed in surrounding maternal tissues hence rendering their isolation a deterring task. Thus, there is a considerable time lag in studying proembryo formation in plants as compared to animal embryology leaving a number of questions of overriding importance, such as: 1: how and when is cell polarity established in the angiosperm egg cell 2: how do molecular processes such as cell division, cell expansion, cell maturation and differentiation unfold which bring the zygote (the progenitor cell of the next sporophytic generation), from the unicellular to the multicellular stage 3: what genes are involved in triggering the first asymmetrical division of the zygote and how these genes are regulated, unanswered. Wheat is a staple crop and prevalent alimentation source in many parts of the world which warrants studies aimed at unravelling mechanisms ultimately responsible for seed set, the prerequisite of which is successful fertilisation of the egg as well as normal endosperm development. A micromanipulation technique based on gamete isolation, electrofusion performed at the gamete cell-pair level and microinjection of isolated wheat egg cells/fusion products was elaborated which permits a complex approach in addressing these issues. Capitalising on this method, one of the earliest marks of fertilisation-associated events, egg activation by the sperm cell through calcium signalling has been dissected together with the in vivo dynamics of the F-actin cytoskeleton shown to be involved in imparting spatial information to the egg cell concerning the micropylar-chalazal axis of the embryo sac. Furthermore, one of the main cell cycle protein kinases, cdc2 kinase, was localised in isolated and in vitro fertilised egg cells of wheat with double labelling the protein of interest and tubulin assisted by fluorescent and confocal microscopy. The importance of the pivotal role played by p34cdc2 in reorganising the intracellular structures of the wheat zygote for rendering it capable of preparing for mitosis that produces the proembryo possessing two cells with distinct cell fates will be discussed as well as the implications of this approach in transcript profiling of isolated wheat female gametes, zygotes, and two-celled embryos in the context of studying cell polarity/asymmetrical cell division.
Dianjing Guo is an associate professor at the Chinese University of Hong Kong. Prior to joining CUHK, she was a senior researcher at the Virginia Bioinformatics Institute. Dianjing received her Ph.D from the Chinese Academy of Science. Her primary research interests are in the field of genomics and computational biology. She has published many research articles in peer reviewed academic journals over the past 10 years.
H2O2 has been recognized as a signal molecule involved in gene expression regulation. Arabidopsis microarray data analysis revealed that about 1–2% of the transcriptome and one-third of the transcription factor mRNA are altered after exposure to H2O2). In the green plant, H2O2 is mainly produced during the process of photosynthesis, respiration, photorespiration, and wound/pathogen-triggered ROS burst. Apart from the ROS burst mediated by membrane-associated NADPH oxidases (rboh A∼F family) under wounding and/or pathogen invasion, the photorespiration and electro transfer during photosynthesis constitute more than 90% of the H2O2 production in healthy mesophyll cells. Both photorespiration and electro transfer during photosynthesis require light, which indicates major H2O2 production is light-dependent. Therefore, a high background level of H2O2 may exist in the light-grown plant, which may interfere with the observation of the H2O2effects in planta. The high background level of endogenous H2O2 in the light-grown seedlings may suggest that the oxidative effect has taken place and interfered with the observation of the H2O2 effects in planta, especially when investigating gene expression. In this study, the light-induced oxidative response was elucidated at the transcriptome level. The transcriptome profiles of plants grown under dark, light, and 5-mM H2O2 treatment under dark were investigated and compared. Each condition contained two biological replicates and total RNA extracted from 7-day-old seedlings were used for microarray analysis (Affymetrix Arabidopsis ATH1 Genome Array Microarray).. In total, 2050 and 8540 genes showed altered expression under H2O2 and light treatment, respectively (p < 0.01), accounting for about 10% and 37.5% of the Arabidopsistranscriptome, respectively. Interestingly, out of the 2050 H2O2-responsive genes, 1595 (77.8%) were also co-regulated by light. Among the 1595 genes, 1027 were up-regulated and 486 were down-regulated by both H2O2 and light, accounting for ∼95% of the co-regulated genes and 73.8% of H2O2-regulated genes. Co-expression was measured as Pearson’s correlation coefficient, which is ∼0.79 between the log2 transferred fold change in expression, indicating a high correlation between these two transcriptome profiles. The fact that a high percentage of H2O2-responsive genes are also regulated by light suggests the existence of H2O2 signaling under normal light conditions in Arabidopsis. The H2O2- and light-co-regulated genes were analyzed using the gene ontology (GO) enrichment plugin tool BiNGO. Over-represented GO categories were found enriched. Both the co-up- and down-regulated gene sets were analyzed for over-represented functions. It was found that co-up-regulated genes are highly related to plastid/nucleus functions and gene regulation function, such as nucleotide binding, protein binding, DNA binding, chromatin binding, transcription regulator activity, transcription process, and DNA metabolism. Other functions such as stress response-related, organelle organization, embryonic, and post-embryonic development were also enriched. Surprisingly, when the 486 co-down-regulated genes were analyzed, only the GO term of ‘response to biotic stress’ was enriched. The GO enrichment analysis indicated the genes co-up-regulated by light and H2O2 are involved in divergent biological processes and molecular functions, especially in gene expression regulation, but not restricted to stress-related. H2O2 is highly abundant in light-grown plants, indicating the active ROS signal pathways. Previous studies have implied the crosstalk between the light and H2O2 signal pathways. For example, Early Light Inducible Protein 2 (ELIP2) and Ascorbate Peroxidase 2 (APX2) genes were activated by both high light and H2O2 treatment, suggesting a H2O2-dependent pathway was involved in light stress signaling. Genome-wide expression study revealed that H2O2 plays a key role in the transcriptional up-regulation of small heat shock proteins during high-light stress. In addition, H2O2 was involved in high blue-light-induced chloroplast avoidance movements in Arabidopsis. These studies have revealed the ROS signal profiles in the high-light situation.