| Development of multicellular organisms is a complex process requiring orchestrated regulations at transcriptional, post-transcriptional, translational, and post-translational levels. Numerous studies have revealed many important genes for different aspects of plant development. Most of these genes encode regulatory proteins, which are involved in various biological processes including gene transcription and signal transduction. The mutations of many of these genes cause defects in morphological or physiological phenotypes. However, the molecular functions of many of them remain poorly understood. Arabidopsis thaliana has been used as the model organism in my projects to investigate the regulatory mechanisms controlling flower and anther development at the transcriptional and post-translational levels.;A number of transcription factor genes have been characterized to be essential for male fertility by regulating anther development at various stages. The DYSFUNCTIONAL TAPETUM 1 (DYT1) and MYB35 genes were reported to regulate the tapetum function and pollen development based on genetic and morphological evidence. The molecular regulatory functions of DYT1 and MYB35 proteins were investigated in one of my research projects and the results suggested that they probably function as transcriptional activators. Transient induction of DYT1 activated the MYB35 transcription rapidly, suggesting that MYB35 may be immediately downstream of DYT1. The DNA binding specificity of the DYT1 protein was investigated using gel-shift assays, and the results revealed that DYT1 binds to a specialized G-box motif TCACGTGA. Combined with the transcriptomic information of dyt1 mutant anthers from our lab, this study consolidated the function of DYT1 in controlling a large number of anther genes, which may explain its importance in tapetum and pollen development.;The ubiquitin-proteasome system (UPS) is involved in almost every biological process. Arabidopsis E3 ubiquitin ligases have been demonstrated to regulate various plant physiological and developmental processes. The ARABIDOPSIS SKP1-LIKE 1 (ASK1) gene, which encodes a key subunit of Skp1-Cul1-F-box (SCF)-type E3 ubiquitin ligases, has been shown to be involved in plant development and reproduction, especially in flower development and meiosis. Despite many lines of genetic evidence, the role of ASK1 in regulating the proteome and transcriptome is still not clear. In my second project, the flower bud proteomes and transcriptomes were compared between an ask1 mutant and wild-type to identify proteins that are putative substrates of the ASK1-containing E3 ubiquitin ligases (ASK1-E3s). Proteins that accumulate to higher levels in the flower bud proteome of the ask1 mutant than that of wild-type, and whose cognate RNA levels are not significantly different between the two genotypes, may be regulated by ASK1-E3s at the post-translational level. The putative substrates include transcription regulators, kinases, peptidases, and interestingly ribosomal proteins, suggesting that regulatory proteins are more likely to be regulated by the UPS and that the ribosomal proteins, which are usually believed to be only involved in protein synthesis, may also be regulated by selective proteolysis mechanisms. Another project investigated the impact of ask1 mutation on the anther transcriptome, and the results suggested that ASK1-E3s may regulate the destabilization of transcription factors to modulate the expression of genes involved in multiple signaling pathways. Therefore, the regulations at the transcriptional and post-translational levels may be coordinated by the ubiquitin system.;These studies not only provided large-scale proteomics and transcriptomics information for further investigations, but also revealed specific functions of certain transcription factors that regulate anther development. Further studies may lead to discoveries of novel functions of the regulatory proteins and the overall properties of the regulatory networks underlying flower development. |
