Ongoing Evolution in the Genus Crocus: Diversity of Flowering Strategies on the Way to Hysteranthy

Species of the genus Crocus are found over a wide range of climatic areas. In natural habitats, these geophytes diverge in the flowering strategies. This variability was assessed by analyzing the flowering traits of the Spanish collection of wild crocuses, preserved in the Bank of Plant Germplasm of Cuenca. Plants of the seven Spanish species were analyzed both in their natural environments (58 native populations) and in common garden experiments (112 accessions). Differences among species observed in the native habitats were maintained under uniform environmental conditions, suggesting a genetic basis for flowering mechanisms. Two eco-morphological types, autumn- and spring-flowering species, share similar patterns of floral induction and differentiation period in summer. The optimal temperature for this process was 23 °C for both types. Unlike Irano-Turanian crocuses, spring-flowering Spanish species do not require low winter temperatures for flower elongation. Hysteranthous crocuses flower in autumn prior to leaf elongation. We conclude that the variability in flowering traits in crocuses is related to the genetic and environmental regulation of flower primordia differentiation and elongation prior to emergence above the soil surface. The elucidation of the physiological differences between eco-morphological types of crocuses: synanthous with cold requirements and synanthous and hysteranthous without cold requirements, unlocks a new approach to the flowering evolution of geophytes in Mediterranean regions. Crocus species can serve both as a new model in the study of the molecular basis of hysteranthy and for the purposes of developing the molecular markers for desirable flowering traits.

AINTEGUMENTA and AINTEGUMENTA-LIKE6 directly regulate floral homeotic and growth genes in young flowers

Arabidopsis flower primordia give rise to floral organ primordia in stereotypical positions within four concentric whorls. Floral organ primordia in each whorl undergo distinct developmental programs to become one of four organ types (sepals, petals, stamens, and carpels). The Arabidopsis transcription factors AINTEGUMENTA (ANT) and AINTEGUMENTA-LIKE6 (AIL6) play critical and partially overlapping roles during floral organogenesis. They are required for correct positioning of floral organ initiation, contribute to the specification of floral organ identity, and regulate the growth and morphogenesis of developing floral organs. To gain insight into the molecular means by which ANT and AIL6 contribute to floral organogenesis, we identified the genome-wide binding sites of both ANT and AIL6 in stage 3 flower primordia, the developmental stage at which sepal primordia become visible and class B and C floral homeotic genes are first expressed. AIL6 binds to a subset of ANT sites, suggesting that AIL6 regulates some but not all of the same target genes as ANT. ANT and AIL6 binding sites are associated with genes involved in many biological processes related to meristem and flower organ development. Comparison of genes associated with both ANT and AIL6 ChIP-Seq peaks and those differentially expressed after perturbation of ANT or AIL6 activity identified likely direct targets of ANT and AIL6 regulation. These include the floral homeotic genes APETALA3 (AP3) and AGAMOUS (AG) and four growth regulatory genes: BIG BROTHER (BB), ROTUNDIFOLIA3 (ROT3), ANGUSTIFOLIA3/GRF INTERACTING FACTOR (AN3/GIF1), and XYLOGLUCAN ENDOTRANSGLUCOLSYLASE/HYDROLASE9 (XTH9).One Sentence SummaryThe transcription factors ANT and AIL6 directly regulate genes involved in different aspects of flower development including genes that specify floral organ identity and those that regulate growth.

Expression and Function Studies of CYC/TB1-Like Genes in the Asymmetric Flower Canna (Cannaceae, Zingiberales)

The asymmetric flower, lacking any plane of symmetry, is rare among angiosperms. Canna indica L. has conspicuously asymmetric flowers resulting from the presence of a half-fertile stamen, while the other androecial members develop as petaloid staminodes or abort early during development. The molecular basis of the asymmetric distribution of fertility and petaloidy in the androecial whorls remains unknown. Ontogenetic studies have shown that Canna flowers are borne on monochasial (cincinnus) partial florescences within a racemose inflorescence, with floral asymmetry likely corresponding to the inflorescence architecture. Given the hypothesized role of CYC/TB1 genes in establishing floral symmetry in response to the influence of the underlying inflorescence architecture, the spatiotemporal expression patterns of three Canna CYC/TB1 homologs (CiTBL1a, CiTBL1b-1, and CiTBL1b-2) were analyzed during inflorescence and floral development using RNA in situ hybridization and qRT-PCR. In the young inflorescence, both CiTBL1a and CiTBL1b-1 were found to be expressed in the bracts and at the base of the lateral florescence branches, whereas transcripts of CiTBL1b-2 were mainly detected in flower primordia and inflorescence primordia. During early flower development, expression of CiTBL1a and CiTBL1b-1 were both restricted to the developing sepals and petals. In later flower development, expression of CiTBL1a was reduced to a very low level while CiTBL1b-1 was detected with extremely high expression levels in the petaloid androecial structures including the petaloid staminodes, the labellum, and the petaloid appendage of the fertile stamen. In contrast, expression of CiTBL1b-2 was strongest in the fertile stamen throughout flower development, from early initiation of the stamen primordium to maturity of the ½ anther. Heterologous overexpression of CiTBL genes in Arabidopsis led to dwarf plants with smaller petals and fewer stamens, and altered the symmetry of mature flowers. These data provide evidence for the involvement of CYC/TB1 homologs in the development of the asymmetric Cannaceae flower.

Study of frost resistance of cherry variety Turgenevka during on different rootstocks winter thaws

Relevance. The study of the resistance of garden cultures to unfavorable abiotic factors of the winter period is a priority direction of scientific studies, because the low winter hardiness can annul advantages the varieties on other signs. Concerning in the middle zone of Russia, studies on the resistance of cherry to frost during the thaw period remain relevant.Methods. The studies were carried out in the laboratory of physiology of fruit plant resistance at VNI-ISPKin2017-2018. The object of research was the Turgenevka cherry variety on new clonal root-stock of the Institute breeding were studied. Control - Turgenevka on the Rubin stock. For artificial freezing in early December the material was prepared for III and IV components of frost hardiness.Results. As a result of artificial freezing, the Turgenevka cherry variety was characterized by frost resistance of vegetative buds and tissues of annual shoots during a three-day winter thaw of + 2°C with a decrease in temperature of -25°C (III component of frost resistance). Inthiscase, thehighest frost resistance of the generative buds of the Turgenevka variety on rootstock 74340, 82987 is shown. After a three-day thaw of +2°C and repeated hardening with a subsequent decrease in temperature to -30°C in March (IV frost resistance component), the Turgenevka variety on the rootstock 74332, 74363, 82987 was characterized by frost resistance of vegetative buds, bark and wood of annualshoots. Moreover, in the studied scion-rootstock combinations, low frost resistance of the generative kidneys was revealed. Only in the studied variety on the rootstock 82987 was the largest percentage of living flower primordia revealed. The conducted studies revealed the Turgenevka variety in a rootstock of 82987 with the greatest potential for frost resistance during the winter thaws.

Inflorescence Development and Floral Organogenesis in Taraxacum kok-saghyz

Rubber dandelion (Taraxacum kok-saghyz Rodin; TK) has received attention for its natural rubber content as a strategic biomaterial, and a promising, sustainable, and renewable alternative to synthetic rubber from fossil carbon sources. Extensive research on the domestication and rubber content of TK has demonstrated TK’s potential in industrial applications as a relevant natural rubber and latex-producing alternative crop. However, many aspects of its biology have been neglected in published studies. For example, floral development is still poorly characterized. TK inflorescences were studied by scanning electron microscopy. Nine stages of early inflorescence development are proposed, and floral micromorphology is detailed. Individual flower primordia development starts at the periphery and proceeds centripetally in the newly-formed inflorescence meristem. Floral organogenesis begins in the outermost flowers of the capitulum, with corolla ring and androecium formation. Following, pappus primordium—forming a ring around the base of the corolla tube—and gynoecium are observed. The transition from vegetative to inflorescence meristem was observed 21 days after germination. This description of inflorescence and flower development in TK sheds light on the complex process of flowering, pollination, and reproduction. This study will be useful for genetics, breeding, systematics, and development of agronomical practices for this new rubber-producing crop.

Mild Water Stress Makes Apple Buds More Likely to Flower and More Responsive to Artificial Forcing— Impacts of an Unusually Warm and Dry Summer in Germany

Climate change may result in increasingly frequent extreme events, such as the unusually dry conditions that occurred in Germany during the apple growing season of 2018. To assess the effects of this phenomenon on dormancy release and flowering in apples, we compared irrigated and non-irrigated orchard blocks at Campus Klein-Altendorf. We evaluated bud development, dormancy release and flowering in the following season under orchard and controlled forcing conditions. Results showed that irrigated trees presented longer (39.2%) and thinner shoots compared to non-irrigated trees. In both treatments, apical buds developed a similar number of flower primordia per cyme (4–5), presenting comparable development and starch dynamics during dormancy. Interestingly, buds on non-irrigated shoots exposed to low chill levels responded earlier to forcing conditions than those on irrigated shoots. However, chill requirements (~50 Chill Portions) and bud phenology under field conditions did not differ between treatments. In spring, buds on non-irrigated trees presented a higher bloom probability (0.42) than buds on irrigated trees (0.30). Our findings show that mild water stress during summer influenced vegetative growth during the same season, as well as the response of buds to forcing temperatures and flowering of the following season. The differences between irrigation levels in the phenological responses of shoots under low-chill conditions point to a so-far understudied impact of water supply on chilling requirements, as well as subsequent bud behavior. Accounting for the effects of both the water status during summer and the temperature during the dormant season may be required for accurately predicting future tree phenology in a changing climate.

Temporal Distinction between Male and Female Floral Organ Development in Nicotiana tabacum cv. Xanthi (Solanaceae)

Early floral developmental investigations provide crucial evidence for phylogenetic and molecular studies of plants. The developmental and evolutionary mechanisms underlying the variations in floral organs are critical for a thorough understanding of the diversification of flowers. Ontogenetic comparisons between anthers and pistil within single flowers were characterized over time in Nicotiana tabacum cv. Xanthi. The ages of 42 tobacco flower or flower primordia were estimated using corolla growth analysis. Results showed that the protodermal layer in carpel primordia contributes to carpel development by both anticlinal and periclinal divisions. Periclinal divisions in the hypodermal layer of the placenta were observed around 4.8 ± 1.3 days after the formation of early carpel primordia (ECP) and ovule initiation occurred 10.0 ± 0.5 days after ECP. Meiosis in anthers and ovules began about 8.9 ± 1.1 days and 14.4 ± 1.3 days after ECP, respectively. Results showed an evident temporal distinction between megasporogenesis and microsporogenesis. Flower ages spanned a 17-day interval, starting with flower primordia containing the ECP and anther primordia to the tetrad stage of meiosis in megasporocytes and the bicellular stage in pollen grains. These results establish a solid foundation for future studies in order to identify the developmental and molecular mechanisms responsible for the mating system in tobacco.

Functional and expressional analyses of apple FLC-like in relation to dormancy progress and flower bud development

We previously identified the FLOWERING LOCUS C (FLC)-like gene, a MADS-box transcription factor gene that belongs to Arabidopsis thaliana FLC clade, in apple (Malus x domestica), and its expression in dormant flower buds is positively correlated with cumulative cold exposure. To elucidate the role of the MdFLC-like in the dormancy process and flower development, we first characterized the phenotypes of MdFLC-like overexpressing lines with the Arabidopsis Columbia-0 background. The overexpression of MdFLC-like significantly delayed the bolting date and reduced the plant size, but it did not significantly affect the number of rosette leaves or flower organ formation. Thus, MdFLC-like may affect vegetative growth and development rather than flowering when expressed in Arabidopsis, which is not like Arabidopsis FLC that affects development of flowering. We compared seasonal expression patterns of MdFLC-like in low-chill ‘Anna’ and high-chill ‘Fuji’ and ‘Tsugaru’ apples collected from trees grown in a cold winter region in temperate zone, and found an earlier up-regulation in ‘Anna’ compared with ‘Fuji’ and ‘Tsugaru’. Expression patterns were also compared in relation to developmental changes in the flower primordia during the chilling accumulation period. Overall, MdFLC-like was progressively up-regulated during flower primordia differentiation and development in autumn to early winter, and reached a maximum expression level at around the same time as the genotype-dependent chilling requirements were fulfilled in high-chill cultivars. Thus, we hypothesize MdFLC-like may be up-regulated in response to cold exposure and flower primordia development during the progress of endodormancy. Our study also suggests MdFLC-like may have a growth inhibiting function during the end of endodormancy and ecodormancy, when the temperature is low and unfavorable for rapid bud outgrowth.

CpWRKY71, a WRKY Transcription Factor Gene of Wintersweet (Chimonanthus praecox), Promotes Flowering and Leaf Senescence in Arabidopsis

The WRKY transcription factors are one of the most important plant-specific transcription factors and play vital roles in various biological processes. However, the functions of WRKY genes in wintersweet (Chimonanthus praecox) are still unknown. In this report, a group IIc WRKY gene, CpWRKY71, was isolated from wintersweet. CpWRKY71 was localized to the nucleus and possessed transcriptional activation activity. qRT-PCR (quantitative real-time PCR) analysis showed that CpWRKY71 was expressed in all tissues tested, with higher expression in flowers and senescing leaves. During the flower development, the highest expression was detected in the early-withering stage, an obvious expression of CpWRKY71 was also observed in the flower primordia differentiation and the bloom stage. Meanwhile, the expression of CpWRKY71 was influenced by various abiotic stress and hormone treatments. The expression patterns of the CpWRKY71 gene were further confirmed in CpWRKY71pro:GUS (β-glucuronidase) plants. Heterologous overexpression of CpWRKY71 in Arabidopsis caused early flowering. Consistent with the early flowering phenotype, the expression of floral pathway integrators and floral meristem identity (FMI) genes were significantly up-regulated in transgenic plants. In addition, we also observed that the transgenic plants of CpWRKY71 exhibited precocious leaf senescence. In conclusion, our results suggested that CpWRKY71 may be involved in the regulation of flowering and leaf senescence in Arabidopsis. Our study provides a foundation for further characterization of CpWRKY genes function in wintersweet, and also enrich our knowledge of molecular mechanism about flowering and senescence in wintersweet.

Diverse Developmental Responses to Warming Temperatures Underlie Changes in Flowering Phenologies

Climate change has resulted in increased temperature means across the globe. Many angiosperms flower earlier in response to rising temperature and the phenologies of these species are reasonably well predicted by models that account for spring (early growing season) and winter temperatures. Surprisingly, however, exceptions to the general pattern of precocious flowering are common. Many species either do not appear to respond or even delay flowering in, or following, warm growing seasons. Existing phenological models have not fully addressed such exceptions to the common association of advancing phenologies with warming temperatures. The phenological events that are typically recorded (e.g., onset of flowering) are but one phase in a complex developmental process that often begins one or more years previously, and flowering time may be strongly influenced by temperature over the entire multi-year course of flower development. We propose a series of models that explore effects of growing-season temperature increase on the multiple processes of flower development and how changes in development may impact the timing of anthesis. We focus on temperate forest trees, which are characterized by preformation, the initiation of flower primordia one or more years prior to anthesis. We then synthesize the literature on flower development to evaluate the models. Although fragmentary, the existing data suggest the potential for temperature to affect all aspects of flower development in woody perennials. But, even for relatively well studied taxa, the critical developmental responses that underlie phenological patterns are difficult to identify. Our proposed models explain the seemingly counter-intuitive observations that warmer growing-season temperatures delay flowering in many species. Future research might concentrate on taxa that do not appear to respond to temperature, or delay flowering in response to warm temperatures, to understand what processes contribute to this pattern.