Radial or bilateral? The molecular basis of floral symmetry.

In the plant kingdom, the flower is one of the most relevant evolutionary novelties. Floral symmetry has evolved multiple times from the ancestral condition of radial to bilateral symmetry. During evolution, several transcription factors have been recruited by the different developmental pathways in relation to the increase of plant complexity. The MYB proteins are among the most ancient plant transcription factor families and are implicated in different metabolic and developmental processes. In the model plant Antirrhinum majus, three MYB transcription factors (DIVARICATA, DRIF, and RADIALIS) have a pivotal function in the establishment of floral dorsoventral asymmetry. Here, we present an updated report of the role of the DIV, DRIF, and RAD transcription factors in both eudicots and monocots, pointing out their functional changes during plant evolution. In addition, we discuss the molecular models of the establishment of flower symmetry in different flowering plants

The MADS and the Beauty: Genes Involved in the Development of Orchid Flowers

Since the time of Darwin, biologists have studied the origin and evolution of the Orchidaceae, one of the largest families of flowering plants. In the last two decades, the extreme diversity and specialization of floral morphology and the uncoupled rate of morphological and molecular evolution that have been observed in some orchid species have spurred interest in the study of the genes involved in flower development in this plant family. As part of the complex network of regulatory genes driving the formation of flower organs, the MADS-box represents the most studied gene family, both from functional and evolutionary perspectives. Despite the absence of a published genome for orchids, comparative genetic analyses are clarifying the functional role and the evolutionary pattern of the MADS-box genes in orchids. Various evolutionary forces act on the MADS-box genes in orchids, such as diffuse purifying selection and the relaxation of selective constraints, which sometimes reveals a heterogeneous selective pattern of the coding and non-coding regions. The emerging theory regarding the evolution of floral diversity in orchids proposes that the diversification of the orchid perianth was a consequence of duplication events and changes in the regulatory regions of the MADS-box genes, followed by sub- and neo-functionalization. This specific developmental-genetic code is termed the “orchid code.

Analysis of the TCP genes expressed in the inflorescence of the orchid Orchis italica

TCP proteins are plant-specific transcription factors involved in many different processes. Because of their involvement in a large number of developmental pathways, their roles have been investigated in various plant species. However, there are almost no studies of this transcription factor family in orchids. Based on the available transcriptome of the inflorescence of the orchid Orchis italica, in the present study we identified 12 transcripts encoding TCP proteins. The phylogenetic analysis showed that they belong to different TCP classes (I and II) and groups (PCF, CIN and CYC/TB1), and that they display a number of conserved motifs when compared with the TCPs of Arabidopsis and Oryza. The presence of a specific cleavage site for the microRNA miRNA319, an important post-transcriptional regulator of several TCP genes in other species, was demonstrated for one transcript of O. italica, and the analysis of the expression pattern of the TCP transcripts in different inflorescence organs and in leaf tissue suggests that some TCP transcripts of O. italica exert their role only in specific tissues, while others may play multiple roles in different tissues. In addition, the evolutionary analysis showed a general purifying selection acting on the coding region of these transcripts

Plant DNA Methylation: An Epigenetic Mark in Development, Environmental Interactions, and Evolution

DNA methylation is an epigenetic modification of the genome involved in the regulation of gene expression and modulation of chromatin structure. Plant genomes are widely methylated, and the methylation generally occurs on the cytosine bases through the activity of specific enzymes called DNA methyltransferases. On the other hand, methylated DNA can also undergo demethylation through the action of demethylases. The methylation landscape is finely tuned and assumes a pivotal role in plant development and evolution. This review illustrates different molecular aspects of DNA methylation and some plant physiological processes influenced by this epigenetic modification in model species, crops, and ornamental plants such as orchids. In addition, this review aims to describe the relationship between the changes in plant DNA methylation levels and the response to biotic and abiotic stress. Finally, we discuss the possible evolutionary implications and biotechnological applications of DNA methylation

Orchid NAC Transcription Factors: A Focused Analysis of CUPULIFORMIS Genes

Plant transcription factors are involved in different developmental pathways. NAC transcription factors (No Apical Meristem, Arabidopsis thaliana Activating Factor, Cup-shaped Cotyledon) act in various processes, e.g., plant organ formation, response to stress, and defense mechanisms. In Antirrhinum majus, the NAC transcription factor CUPULIFORMIS (CUP) plays a role in determining organ boundaries and lip formation, and the CUP homologs of Arabidopsis and Petunia are involved in flower organ formation. Orchidaceae is one of the most species-rich families of angiosperms, known for its extraordinary diversification of flower morphology. We conducted a transcriptome and genome-wide analysis of orchid NACs, focusing on the No Apical Meristem (NAM) subfamily and CUP genes. To check whether the CUP homologs could be involved in the perianth formation of orchids, we performed an expression analysis on the flower organs of the orchid Phalaenopsis aphrodite at different developmental stages. The expression patterns of the CUP genes of P. aphrodite suggest their possible role in flower development and symmetry establishment. In addition, as observed in other species, the orchid CUP1 and CUP2 genes seem to be regulated by the microRNA, miR164. Our results represent a preliminary study of NAC transcription factors in orchids to understand the role of these genes during orchid flower formation

Transcriptome-wide identification and expression analysis of DIVARICATA- and RADIALIS-like genes of the Mediterranean orchid Orchis italica.

Bilateral symmetry of flowers is a relevant novelty that has occurred many times throughout the evolution of flowering plants. In Antirrhinum majus, establishment of flower dorso-ventral asymmetry is mainly due to interaction of TCP (CYC and DICH) and MYB (DIV, RAD and DRIF) transcription factors. In the present study, we characterized 8 DIV-, 4 RAD- and 2 DRIF-like genes from the transcriptome of Orchis italica, an orchid species with bilaterally symmetric and resupinate flowers. We found a similar number of DIV- and RAD-like genes within the genomes of Phalaenopsis equestris and Dendrobium catenatum orchids. Orchid DIV- and RAD-like proteins share conserved motifs whose distribution reflects their phylogeny and analysis of the genomic organization revealed a single intron containing many traces of transposable elements. Evolutionary analysis has shown that purifying selection acts on the DIV- and RAD-like coding regions in orchids, with relaxation of selective constraints in a branch of the DIV-like genes. Analysis of the expression patterns of DIV- and RAD-like genes in O. italica revealed possible redundant functions for some of them. In the perianth of O. italica, the ortholog of DIV and DRIF of A. majus are expressed in all tissues, whereas RAD is mainly expressed in the outer tepals and lip. These data allow for proposal of an evolutionary conserved model in which the expression of the orthologs of the DIV, RAD and DRIF genes might be related to establishment of flower bilateral symmetry in the non-model orchid species O. italica

ISSR markers show differentiation among Italian populations of Asparagus acutifolius L

BACKGROUND: Asparagus acutifolius L. is a dioecious and native plant species, widely distributed in the Mediterranean Basin. It is known for its fine flavour and could represent an important resource for cultivation programs in desert areas. Few molecular studies have been performed on this species. In the present paper, the ISSR technique was employed to study genetic diversity in Italian A. acutifolius. RESULTS: Twenty-three primers produced a total of 228 polymorphic fragments used to evaluate genetic variation. F(ST )(0.4561) and Theta B (0.4776) values indicate a wide genetic variation among the samples examined. The distance UPGMA tree grouped together the genotypes strictly according to their geographical origin, showing that each sample is genetically structured and can be considered a distinct population. AMOVA analysis further confirmed genetic structuring of the populations. Population-specific fragments were also detected. CONCLUSION: The results suggest that ISSR markers are useful in distinguishing the populations of A. acutifolius according to geographical origin, and confirm the importance of genetic studies for designing germplasm conservation strategies

Extending the toolkit for beauty: Differential co-expression of DROOPING LEAF-like and class B MADS-box genes during Phalaenopsis flower development

The molecular basis of orchid flower development is accomplished through a specific regulatory program in which the class B MADS-box AP3/DEF genes play a central role. In particular, the differential expression of four class B AP3/DEF genes is responsible for specification of organ identities in the orchid perianth. Other MADS-box genes (AGL6 and SEP-like) enrich the molecular program underpinning the orchid perianth development, resulting in the expansion of the original "orchid code" in an even more complex gene regulatory network. To identify candidates that could interact with the AP3/DEF genes in orchids, we conducted an in silico differential expression analysis in wild-type and peloric Phalaenopsis. The results suggested that a YABBY DL-like gene could be involved in the molecular program leading to the development of the orchid perianth, particularly the labellum. Two YABBY DL/CRC homologs are present in the genome of Phalaenopsis equestris, PeDL1, and PeDL2, and both express two alternative isoforms. Quantitative real-time PCR analyses revealed that both genes are expressed in column and ovary. In addition, PeDL2 is more strongly expressed the labellum than in the other tepals of wild-type flowers. This pattern is similar to that of the AP3/DEF genes PeMADS3/4 and opposite to that of PeMADS2/5. In peloric mutant Phalaenopsis, where labellum-like structures substitute the lateral inner tepals, PeDL2 is expressed at similar levels of the PeMADS2-5 genes, suggesting the involvement of PeDL2 in the development of the labellum, together with the PeMADS2-PeMADS5 genes. Although the Yeast Two-Hybrid analysis does not reveal the ability of PeDL2 to bind the PeMADS2-PeMADS5 proteins directly, the existence of regulatory interactions is suggested by the presence of CArG-boxes and other MADS-box transcription factor binding sites within the putative promoter of the orchid DL2 gene

Epidemiology of Noble Pen Shell (Pinna nobilis L. 1758) Mass Mortality Events in Adriatic Sea Is Characterised with Rapid Spreading and Acute Disease Progression

From May to October 2019, multiple mass mortality events (MMEs) of Pinna nobilis were observed along Croatian coastline starting from the south-east and rapidly progressing in north-western direction. Time dynamics of the MMEs closely followed general speed and direction patterns of surface sea-currents, advancing approximately 350 km in less than 3 months. Surveillance, clinical evaluation, and sample collection were performed on multiple sites with various degrees of mortality rates. Moribund P. nobilis individuals were collected and subjected to pathological, molecular, and microscopical investigation. Affected animals were positive for Mycobacterium in 70% of the individuals, and Haplosporidium pinnae was present in 58% of the cases. Observed pathological lesions were most severe where concurrent presence of both pathogens was confirmed (in 45.8% of moribund individuals). Moderate to strong lesions were observed in animals positive for Mycobacterium only (25% of cases), and lesions were absent or minor to moderate when only H. pinnae was confirmed (16% of cases). Considering the rapid and severe spread of the MMEs, the areas less exposed to major sea currents appeared to be at lower risk of pathogen transmission. Surveillance activities along the Croatian coastline identified several P. nobilis populations in such “lower risk” areas without apparent mortality or clinical symptoms. Such areas are of particular interest as source of potentially healthy individuals to support active recovery actions

Flavonoids profile and antioxidant activity in flowers and leaves of hawthorn species (Crataegus spp.) from different regions of Iran

This study was undertaken to determine the total quantity of phenolic and flavonoids, as well as to find out about the HPLC quantification of some individual phenolic compounds (i.e. chlorogenic acid, vitexin 2"-O-rhamnoside, vitexin, rutin, hyperoside, quercetin, and isoquercetin) in flowers and leaves of 56 samples of different hawthorn species (Crataegus spp.) collected from different geographical regions of Iran. The amount of total phenolics ranges from 7.21 to 87.73 mg GAE/g in dry weight of the plant, and the total amount of flavonoids varied amongst species and in different plant organs ranging from 2.27 to 17.40 mg/g dry weight. Chlorogenic acid, vitexin, and vitexin 2"-O-rhamnoside were found to be the most abundant phenolic compounds in the extracts of hawthorn leaves. Meanwhile, chlorogenic acid, hyperoside, and rutin were the most abundant phenolic compounds in the extracts of hawthorn flowers in most genotypes. The antioxidant activity widely varied in species and in different organs of each individual plant, ranging from 0.9 to 4.65 mmol Fe++/g DW plant, calculated through the ferric-reducing antioxidant power (FRAP) method. Thus, this could provide valuable data for developing breeding strategies and plans; it can also help us in selecting genotypes with high phenolic contents for producing natural antioxidants and other bioactive compounds beneficial for food or the pharmaceutical industries