The Relationship between AGAMOUS and Cytokinin Signaling in the Establishment of Carpeloid Features

Gynoecium development is dependent on gene regulation and hormonal pathway interactions. The phytohormones auxin and cytokinin are involved in many developmental programs, where cytokinin is normally important for cell division and meristem activity, while auxin induces cell differentiation and organ initiation in the shoot. The MADS-box transcription factor AGAMOUS (AG) is important for the development of the reproductive structures of the flower. Here, we focus on the relationship between AG and cytokinin in Arabidopsis thaliana, and use the weak ag-12 and the strong ag-1 allele. We found that cytokinin induces carpeloid features in an AG-dependent manner and the expression of the transcription factors CRC, SHP2, and SPT that are involved in carpel development. AG is important for gynoecium development, and contributes to regulating, or else directly regulates CRC, SHP2, and SPT. All four genes respond to either reduced or induced cytokinin signaling and have the potential to be regulated by cytokinin via the type-B ARR proteins. We generated a model of a gene regulatory network, where cytokinin signaling is mainly upstream and in parallel with AG activity.

Transcription factor action orchestrates the complex expression pattern ofCRABS CLAW, a gynoecium developmental regulator in Arabidopsis

The flower of angiosperms is the most complex organ that plants generate and many transcription factors (TFs) are involved to regulate its morphogenesis in a coordinated way. In its center, the gynoecium develops consisting of specialized tissues such as secondary meristems, sites of postgenital fusion, ovules, pollen transmitting tract, all to assure successful sexual reproduction. Gynoecium development requires tight regulation of developmental regulators across time and tissues. However, while we know of several examples how simple on/off regulation of gene expression is achieved in plants, it remains unclear which regulatory processes generate complex expression patterns. Here, we use the gynoecium developmental regulatorCRABS CLAW (CRC)from Arabidopsis to study regulatory mechanisms contributing to its sophisticated expression pattern. Using a combination ofin silicopromoter analyses, global TF-DNA interaction screens, co-expression and mutant analysis we find that miRNA action, DNA methylation, and chromatin remodeling do not contribute substantially toCRCregulation. We show that a plethora of TFs bind to theCRCpromoter to fine-tune transcript abundance by activation of transcription, linkingCRCto specific developmental processes but not biotic or abiotic stress. Interestingly, the temporal-spatial aspects of regulation of expression may be under the control of redundantly acting genes and may require higher order complex formation at TF binding sites. We conclude that endogenous regulation of complex expression pattern of Arabidopsis genes requires orchestrated transcription factor action on several conserved promotor sites over almost 4 kb in length.Significance statementDifferent to genes that are simply switched on or off, depending on an environmental cue we find that genes directing development in plants often show complex expression pattern dependent on internal factors only. Here, we addressed the question how an complex expression pattern is achieved and use theCRABS CLAW (CRC)gene required for gynoecium development as an example. Combining wet lab experiments andin silicoanalysis we find that epigenetic regulation plays only a minor role and that a large number of transcription factors activates the transcription ofCRC. Single regulators may have a profound effect onCRCtranscript abundance but less so on the pattern of expression. Complex patterns most likely require the interplay of several transcription factors.

High-resolution temporal transcript profiling during Arabidopsis thaliana gynoecium morphogenesis uncovers the chronology of gene regulatory network activity and reveals novel developmental regulators

The gynoecium is the most complex organ formed by the flowering plants. It encloses the ovules, provides a surface for pollen contact and self-incompatibility reactions, allows pollen tube growth and, post fertilization, and develops into the fruit. Consequently, the regulation of gynoecium morphogenesis is complex and appropriate timing of this process in part determines reproductive success. However, little is known about the global control of gynoecium development, even though many regulatory genes have been characterized. Here, we characterized dynamic gene expression changes using laser-microdissected gynoecium tissue from four developmental stages in Arabidopsis. We provide a high-resolution map of global expression dynamics during gynoecium morphogenesis and link these to the gynoecium interactome. We reveal groups of genes acting together early and others acting late in morphogenesis. Clustering of co-expressed genes enables comparisons between the leaf, shoot apex, and gynoecium transcriptomes allowing the dissection of common and distinct regulators. Furthermore, our results lead to the discovery of the LESSER FERTILITY1-4 (LEF1-4) genes, which, when mutated, lead to impaired gynoecium expansion, illustrating that global transcriptome analyses reveal yet unknown developmental regulators. Our data show that highly interacting proteins, such as SEPALLATA3, AGAMOUS, and TOPLESS are expressed more evenly during development, but switch interactors in time, whereas stage-specific proteins have only few interactors. Our analysis connects specific transcriptional regulator activities, protein interactions, and underlying metabolic processes towards the development of a dynamic network model for gynoecium development.

Anatomy and RNA-Seq reveal important gene pathways regulating sex differentiation in a functionally Androdioecious tree, Tapiscia sinensis

Background Gametogenesis is a key step in the production of ovules or pollen in higher plants. The sex-determination aspects of gametogenesis have been well characterized in the model plant Arabidopsis. However, little is known about this process in androdioecious plants. Tapiscia sinensis Oliv. is a functionally androdioecious tree, with both male and hermaphroditic individuals. Hermaphroditic flowers (HFs) are female-fertile flowers that can produce functional pollen and set fruits. However, compared with male flowers (MFs), the pollen viability and number of pollen grains per flower are markedly reduced in HFs. MFs are female-sterile flowers that fail to set fruit and that eventually drop. Results Compared with HF, a notable cause of MF female sterility in T. sinensis is when the early gynoecium meristem is disrupted. During the early stage of HF development (stage 6), the ring meristem begins to form as a ridge around the center of the flower. At this stage, the internal fourth-whorl organ is stem-like rather than carpelloid in MF. A total of 52,945 unigenes were identified as transcribed in MF and HF. A number of differentially expressed genes (DEGs) and metabolic pathways were detected as involved in the development of the gynoecium, especially the ovule, carpel and style. At the early gynoecium development stage, DEGs were shown to function in the metabolic pathways regulating ethylene biosynthesis and signal transduction (upstream regulator), auxin, cytokinin transport and signalling, and sex determination (or flower meristem identity). Conclusions Pathways for the female sterility model were initially proposed to shed light on the molecular mechanisms of gynoecium development at early stages in T. sinensis.