Cloning and expression analysis of a Petunia hybrida flower specific mitotic-like cyclin

Abscisic acid mediates the reduction of petunia flower size at elevated temperatures due to reduced cell division

Elevated temperatures suppress cell division in developing petunia buds leading to smaller flowers, mediated by ABA. Flower size is one of the most important showy traits in determining pollinator attraction, and a central factor determining the quality of floricultural products. Whereas the adverse effects of elevated temperatures on showy traits have been described in detail, its underlining mechanisms is poorly understood. Here, we investigated the physiological mechanism responsible for the reduction of flower size in petunia under elevated temperatures. We found that the early stages of flower-bud development were most sensitive to elevated temperatures, resulting in a drastic reduction of flower diameter that was almost independent of flower load. We demonstrated that the temperature-mediated flower size reduction occurred due to a shorter growth period, and a lower rate of corolla cell division. Consistently, local application of cytokinin, a phytohormone that promotes cell division, resulted in recovery of flower dimensions when grown under elevated temperatures. Hormone analysis of temperature-inhibited flower buds revealed no significant changes in levels of cytokinin, and a specific increase of abscisic acid (ABA) levels, known to inhibit cell division. Moreover, local application of ABA on flower buds caused a reduction of flower dimensions as a result of lower levels of cell division, suggesting that ABA mediates the reduction of flower size at elevated temperatures. Taken together, our results shed light on the mechanism by which elevated temperatures decrease petunia flower size, and show that temperature-mediated reduction of flower size can be alleviated by increasing the cytokinin/ABA ratio.

Two cyclin Bs are differentially modulated by glucose and sucrose during maize germination

Cell proliferation during seed germination is determinant for an appropriate seedling establishment. The present work aimed to evaluate the participation of two maize B-type Cyclins during germination and under the stimulus of two simple sugars: sucrose and glucose. We found out that the corresponding genes, ZmCycB1;2 and ZmCycB2;1, increased their expression at 24 h of germination, but only ZmCycB1;2 responded negatively to sugar type at the highest sugar concentration tested (120 mM). Also, CycB1;2 showed differential protein levels along germination in response to sugar, or its absence. Both CycBs interacted with CDKA;1 and CDKB1;1 by pull down assays. By an immunoprecipitation approach, it was found that each CycB associated with two CDKB isoforms (34 and 36 kDa). A higher proportion of CycB1;2-CDKB-36kDa was coincident to an increased kinase activity in the presence of sugar and particularly in glucose treatment at 36 h of imbibition. CycB1;2-CDKB activity increased in parallel to germination advance and this was dependent on sugar: glucose > sucrose > No sugar treatment. At RAM, CycB1;2 was more abundant in nuclei on Glucose at late germination; DNA-CycB1;2 colocalization was parallel to CycB1;2 inside the nucleus. Overall, results point out CycB1;2 as a player on promoting proliferation during germination by binding a specific CDKB isoform partner and changing its cellular localization to nuclei, co-localizing with DNA, being glucose a triggering signal.

Expression Profiles of ANGUSTIFOLIA3 and SHOOT MERISTEMLESS, Key Genes for Meristematic Activity in a One-Leaf Plant Monophyllaea glabra, Revealed by Whole-Mount In Situ Hybridization

Members of the genus Monophyllaea are unique in that they produce no new organ during the vegetative phase in the shoot; instead, one of the cotyledons grows indeterminately. The mechanism of this unique trait is unclear, in part because of the lack of suitable assessment techniques. We therefore established a whole-mount in situ hybridization technique, a powerful means of examining spatial patterns in gene expression, for Monophyllaea glabra. By using this, we examined the expression pattern of a SHOOT MERISTEMLESS (STM) ortholog, which is indispensable for the formation and maintenance of the shoot apical meristem (SAM) in typical angiosperms. Expression was confined to the groove meristem (GM), which corresponds to the SAM. We also assessed the expression pattern of ANGUSTIFOLIA3 (AN3), a key promoter for cell division in the leaf meristem. It was expressed not only in the basal meristem (BM) tissue with active cell division in the basal part of the growing cotyledon but also in the GM. The findings suggest that the unusual gene expression pattern of the GM underpins the fuzzy morphogenesis of Monophyllaea.

Transcriptomic and GC-MS Metabolomic Analyses Reveal the Sink Strength Changes during Petunia Anther Development

Petunia, which has been prevalently cultivated in landscaping, is a dicotyledonous herbaceous flower of high ornamental value. Annually, there is a massive worldwide market demand for petunia seeds. The normal development of anther is the necessary prerequisite for the plants to generate seeds. However, the knowledge of petunia anther development processes is still limited. To better understand the mechanisms of petunia anther development, the transcriptomes and metabolomes of petunia anthers at three typical development stages were constructed and then used to detect the gene expression patterns and primary metabolite profiles during the anther development processes. Results suggested that there were many differentially-expressed genes (DEGs) that mainly participated in photosynthesis and starch and sucrose metabolism when DEGs were compared between the different development stages of anthers. In this study, fructose and glucose, which were involved in starch and sucrose metabolism, were taken as the most important metabolites by partial least-squares discriminate analysis (PLS-DA). Additionally, the qRT-PCR analysis of the photosynthetic-related genes all showed decreased expression trends along with the anther development. These pieces of evidence indicated that the activities of energy and carbohydrate metabolic pathways were gradually reduced during all the development stages of anther, which affects the sink strength. Overall, this work provides a novel and comprehensive understanding of the metabolic processes in petunia anthers.

An anther-specific gene PhGRP is regulated by PhMYC2 and causes male sterility when overexpressed in petunia anthers

An anther-specific GRP gene, regulated by PhMYC2 , causes a significant reduction of male fertility when overexpressed in petunia, and its promoter is efficient in genetic engineering of male-sterile lines. Glycine-rich proteins (GRPs) play important roles in plant anther development; however, the underlying mechanisms and related regulatory networks are poorly understood. In this study, a novel glycine-rich family gene designated as PhGRP was isolated from Petunia hybrida 'Fantasy Red'. The qRT-PCR analysis showed that it expressed specifically in anthers, and its expression peaked earlier than those well-known tapetum-specific genes, such as TA29, and several genes with the classic cis-regulatory element 'anther-box' in petunia during its anther development. The male fertility was significantly reduced in PhGRP overexpression lines, due to the abnormal formation of pollen wall. The PhGRP promoter (pPhGRP) could drive the GUS genes expressing specifically in the anthers of the transgenic Arabidopsis plants, indicating that the anther-specific characteristic of this promoter was conserved. In addition, when pPhGRP was used to drive the expression of BARNASE, complete male-sterile petunia lines were created without changes in vegetative organs and floral parts other than anthers. Finally, when pPhGRP was used as the bait to screen a yeast-one-hybrid (Y1H) library, a transcription factor (PhMYC2) belonging to the bHLH family was successfully selected, and the binding between pPhGRP and PhMYC2 was validated both by Y1H and dual-luciferase reporter assay. Overall, these results suggest that PhGRP, which is a male fertility-related gene that expresses specifically in anthers, is regulated by PhMYC2 and whose promoter can be used as an effective tool in the creation of male-sterile lines.

Molecular physiology of adventitious root formation in Petunia hybrida cuttings: involvement of wound response and primary metabolism

Adventitious root formation (ARF) in the model plant Petunia hybrida cv. Mitchell has been analysed in terms of anatomy, gene expression, enzymatic activities and levels of metabolites. This study focuses on the involvement of wound response and primary metabolism. Microscopic techniques were complemented with targeted transcript, enzyme and metabolite profiling using real time polymerase chain reaction (PCR), Northern blot, enzymatic assays, chromatography and mass spectrometry. Three days after severance from the stock plants, first meristematic cells appeared which further developed into root primordia and finally adventitious roots. Excision of cuttings led to a fast and transient increase in the wound-hormone jasmonic acid, followed by the expression of jasmonate-regulated genes such as cell wall invertase. Analysis of soluble and insoluble carbohydrates showed a continuous accumulation during ARF. A broad metabolite profiling revealed a strong increase in organic acids and resynthesis of essential amino acids. Substantial changes in enzyme activities and metabolite levels indicate that specific enzymes and metabolites might play a crucial role during ARF. Three metabolic phases could be defined: (i) sink establishment phase characterized by apoplastic unloading of sucrose and being probably mediated by jasmonates; (ii) recovery phase; and (iii) maintenance phase, in which a symplastic unloading occurs.

Changes in gene expression during male meiosis in Petunia hybrida

We analyzed changes in gene expression during male meiosis in Petunia by combining the meiotic staging of pollen mother cells from a single anther with cDNA-AFLP transcript profiling of mRNA from the synchronously developing sister anthers. The transcript profiling experiments focused on the identification of genes with a modulated expression profile during meiosis, while premeiotic archesporial cells and postmeiotic microspores served as a reference. About 8000 transcript tags, estimated at 30% of the total transcriptome, were generated, of which around 6% exhibited a modulated gene expression pattern at meiosis. Cluster analysis revealed a transcriptional cascade that coincides with the initiation and progression through all stages of the two meiotic divisions. Fragments that exhibited high expression specifically during meiosis I were characterized further by sequencing; 90 out of the 293 sequenced fragments showed homology with known genes, belonging to a wide range of gene classes, including previously characterized meiotic genes. In-situ hybridization experiments were performed to determine the spatial expression pattern for five selected transcript tags. Its concurrence with cDNA-AFLP transcript profiles indicates that this is an excellent approach to study genes involved in specialized processes such as meiosis. Our data set provides the potential to unravel unique meiotic genes that are as yet elusive to reverse genetics approaches.

Meiosis: inducing variation by reduction

A brief introduction is presented with some thought on the origin of meiosis. Subsequently, a sequential overview of the diverse processes that take place during meiosis is provided, with an eye to similarities and differences between the different eukaryotic systems. In the final part, we try to summarize the available core meiotic mutants and make a comprehensive comparison for orthologous genes between fungal, plant, and animal systems.

Sex-Specific Cell Division during Development of Unisexual Flowers in the Dioecious Plant Silene latifolia

We analyzed cell division patterns during the differentiation of unisexual flowers of the dioecious plant Silene latifolia using in situ hybridization with histone H4 and cyclin A1 genes. The gene expression patterns indicated that the activation of cell divisions in whorls 3 and 4 was reversed in young male and female flower buds. During maturation of flower buds, a remarkable reduction in cell division activity occurred in the male gynoecium primordium and female stamen primordia. Our analyses showed that differential activation and reduction of cell division strongly correlated with sex-specific promotion and cessation in the sex differentiation of unisexual flowers.