Petal Asymmetry Research Articles

Transcriptomic Analysis Suggests Auxin Regulation in Dorsal-Ventral Petal Asymmetry of Wild Progenitor Sinningia speciosa.

The establishment of dorsal–ventral (DV) petal asymmetry is accompanied by differential growth of DV petal size, shape, and color differences, which enhance ornamental values. Genes involved in flower symmetry in Sinningia speciosa have been identified as CYCLOIDEA (SsCYC), but which gene regulatory network (GRN) is associated with SsCYC to establish DV petal asymmetry is still unknown. To uncover the GRN of DV petal asymmetry, we identified 630 DV differentially expressed genes (DV-DEGs) from the RNA-Seq of dorsal and ventral petals in the wild progenitor, S. speciosa ‘ES’. Validated by qRT-PCR, genes in the auxin signaling transduction pathway, SsCYC, and a major regulator of anthocyanin biosynthesis were upregulated in dorsal petals. These genes correlated with a higher endogenous auxin level in dorsal petals, with longer tube length growth through cell expansion and a purple dorsal color. Over-expression of SsCYC in Nicotiana reduced petal size by regulating cell growth, suggesting that SsCYC also controls cell expansion. This suggests that auxin and SsCYC both regulate DV petal asymmetry. Transiently over-expressed SsCYC, however, could not activate most major auxin signaling genes, suggesting that SsCYC may not trigger auxin regulation. Whether auxin can activate SsCYC or whether they act independently to regulate DV petal asymmetry remains to be explored in the future.

LOVE ON WINGS, a Dof family protein regulates floral vasculature in Vigna radiata

BackgroundThe interaction among plants and their pollinators has been a major factor which enriched floral traits known as pollination syndromes and promoted the diversification of flowering plants. One of the bee-pollination syndromes in Faboideae with keel blossoms is the formation of a landing platform by wing and keel petals. However, the molecular mechanisms of elaborating a keel blossom remain unclear.ResultsBy performing large scale mutagenesis, we isolated and characterized a mutant in Vigna radiata, love on wings (low), which shows developmental defects in petal asymmetry and vasculature, leading to a failure in landing platform formation. We cloned the locus through map-based cloning together with RNA-sequencing (RNA-seq) analysis. We found that LOW encoded a nucleus-localized Dof-like protein and was expressed in the flower provascular and vascular tissues. A single copy of LOW was detected in legumes, in contrast with other taxa where there seems to be at least 2 copies. Thirty one Dof proteins have been identified from the V. radiata’s genome, which can be further divided into four Major Cluster of Orthologous Groups (MCOGs). We also showed that ectopic expression of LOW in Arabidopsis driven by its native promoter caused changes in petal vasculature pattern.ConclusionsTo summarize, our study isolated a legume Dof-like factor LOW from V. radiata, which affects vasculature development in this species and this change can, in turn, impact petal development and overall morphology of keel blossom.

Functional study of TCP23 in Arabidopsis thaliana during plant development

The TCP class of genes is found only in plants and is represented by the first three identified genes: teosinte branched 1, cycloidea and pcf. Members belonging to this class are important regulators of plant growth, development and control multiple traits in diverse plant species, including flower and petal asymmetry, plant architecture, leaf morphogenesis and senescence, embryo growth and circadian rhythm. Here we described a member of the TCP-P subfamily called AtTCP23. Using qRT-PCR we present evidence that AtTCP23 is ubiquitously express in all organs examined. To ascertain AtTCP23 localization, we fused GFP at the C-terminal position and analyzed stable expression by confocal microscopy. Transgenic lines harboring the full-length protein (OxTCP23:GFP) seems to accumulate GFP in the nucleus. In order to analyze AtTCP23 function, we obtained a T-DNA insertional line and developed AtTCP23 over-expression (OxTCP23) lines. Phenotypic analysis indicates that tcp23-1 knockout line has an early-flowering phenotype while overexpression lines (OxTCP23 and OxTCP23:eGFP) presents opposite phenotype. Besides that those lines have leaf morphology alteration, pale leaf borders and smaller roots. Thus we propose in this study that AtTCP23 may be involved in flowering time control and plant development.

Growth dynamics underlying petal shape and asymmetry.

Development commonly involves the generation of complex shapes from simpler ones. One way of following this process is to use landmarks to track the fate of particular points in a developing organ, but this is limited by the time over which it can be monitored. Here we use an alternative method, clonal analysis, whereby dividing cells are genetically marked and their descendants identified visually, to observe the development of Antirrhinum (snapdragon) petals. Clonal analysis has previously been used to estimate growth parameters of leaves and Drosophila wings but these results were not integrated within a dynamic growth model. Here we develop such a model and use it to show that a key aspect of shape--petal asymmetry--in the petal lobe of Antirrhinum depends on the direction of growth rather than regional differences in growth rate. The direction of growth is maintained parallel to the proximodistal axis of the flower, irrespective of changes in shape, implying that long-range signals orient growth along the petal as a whole. Such signals may provide a general mechanism for orienting growth in other growing structures.

No relationship between fluctuating asymmetry and fitness in Lychnis viscaria

Several earlier studies have indicated a negative relationship between fluctuating asymmetry (FA) and fitness. We tested this assumption by investigating the association between petal asymmetry and several fitness-related characters among natural and common garden populations of Lychnis viscaria. Neither seed set, germination percentage nor the growth rate of seedlings were related to the level of flower asymmetry either among natural populations or in common garden conditions. The only significant association found was a positive connection between petal asymmetry and seed mass measured from natural populations. Thus, in contrary to many earlier published reports, we did not find any evidence for a negative relationship between FA and fitness even if we controlled for measurement error, we had adequate sample size and we measured these characters in two environments. This suggests that FA is not consistently related to individual quality and fitness.

Developmental instability in hybrids between Lychnis viscaria and Lychnis alpina (Caryophyllaceae)

Developmental instability shown by increased fluctuating asymmetry can be caused by either genetic or environmental stress. Genomic coadaptation and heterozygosity are the genetic factors that are commonly assumed to increase the level of developmental stability. Therefore, in hybrid populations the level of fluctuating asymmetry (FA) can be lower due to higher heterozygosity or higher due to disruption of coadapted gene complexes, depending on the degree of divergence between hybridizing taxa. Here I present data on FA in petals from hybrids between Lychnis viscaria (Caryophyllaceae) and Lychnis alpina and from parental species grown in a common garden environment. Petal asymmetry of hybrids was clearly higher than that of either parental species grown in common environment. Between the two parental species petal asymmetry did not differ. The mean size of the petals in hybrids was about the same as in L. viscaria, thus indicating no heterotic effect. Therefore, it seems that hybrids between L. viscaria and L. alpina do suffer from the disruption of coadapted gene complexes as indicated by higher developmental instability.

Morphological Developmental Stability in Plants: Patterns and Causes.

Minor bilateral or radial asymmetry of leaves or flowers, the frequency of phenodeviants, intraindividual variation in repeated characters, and fractal dimensions of morphology are considered to represent measures of developmental instability since deviations from regularity of the phenotype constitute a measure of the inability to maintain developmental precision during ontogeny. First, we review patterns of fluctuating asymmetry in plants and show that levels of asymmetry are considerably greater than in animals. While petal asymmetry tends to decrease with petal size within species, leaf asymmetry tends to increase with leaf size. Intraspecific correlations of petal asymmetry and leaf asymmetry are weakly positive. Second, a meta-analysis of the effects of environmental factors hypothesized to increase asymmetry in leaves and flowers, such as radiation, ultraviolet light, excess artificial fertilizer, pollutants, extreme saline conditions, herbivory, and competition, showed intermediate (i.e., explaining 10% of the variance) to large (i.e., explaining 25% of the variance) effects. Third, a meta-analysis of the effects of genetic factors hypothesized to contribute to increased asymmetry in plants, such as homozygosity, hybridization, mutation, and quantitative genetic differences among individuals, showed variable but usually significant effects, although the number of studies generally was small. Controlled experimental studies of environmental and genetic effects on developmental instability of plants may increase our understanding of the mechanisms causing developmental instability.

Bumblebee preference for symmetrical flowers.

Fluctuating asymmetry, which represents small random deviations from otherwise bilateral symmetry, is a measure of the phenotypic quality of individuals indicating the ability of controlled development under given environmental and genetic conditions. I tested whether floral symmetry reliably reflects phenotypic quality measured in terms of pollinator rewards and whether pollinators respond to floral symmetry in a series of observations and experiments on Epilobium angustifolium (Onagraceae). Lower petal asymmetry was negatively related to mean lower petal length, whereas asymmetry in leaf width was positively related to mean leaf width. Flowers visited by bumblebees were larger and more symmetrical than the nearest neighboring flower. This relationship between pollinator preference for large and symmetrical flowers was demonstrated to be causal in experiments in which the lower petals were manipulated symmetrically or asymmetrically. Nectar production was larger in symmetrical flowers, and this may explain the bumblebee preference for flower symmetry. Floral symmetry therefore reliably reflects nectar production and hence enhances pollen transport. Extensive embryo abortion has been documented in E. angustifolium and other outcrossing plant species. Floral fluctuating asymmetry, which reflects general developmental homeostasis, may explain such developmental selection in these plants.