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Architectural analysis describes the position and fate (vegetative or floral) of plant meristems to account for differences in meristem sensitivity to stimuli depending on developmental stage and position on the plant. To provide further insight into the flowering responses of long-day strawberries to nitrogen (N), photoperiod and light source, ‘Albion’ strawberry plants were conditioned with 100 or 800 ppm N under ND (natural daylength) or LD (long days, natural days plus 24-hr supplementary illumination provided by either 60- or 7-watt incandescent bulbs) and greenhouse growth was evaluated for a total of 10 weeks following conditioning. After greenhouse forcing, plants were dissected and their floral architecture evaluated. Additional plants were established in early July in off-season plasticulture production where fruit, crown and stolon production were evaluated. Both light sources were equally effective in eliciting long-day photoperiod responses. No photoperiod effect on floral precocity, leaf, crown, or runner production was observed during greenhouse forcing. Plants under ND tended to produce more inflorescences during the first 5 weeks while LD enhanced inflorescence and flower production during the last 3 weeks of forcing. In dissected plants, maximum floral initiation was observed in plants receiving elevated N under LD. LD inhibited branch crown formation, but had no effect on the number of vegetative, floral or stolon producing axillary meristems regardless of N treatment. LD conditioning enhanced early yield (through 4 September). Field stolon and branch crown formation was supressed in plants receiving low N with LD conditioning. Stolon and branch crown inhibition by LD conditioning was not observed with elevated N. Growth data combined with architectural mapping of meristems allows more conclusive statements regarding treatment effects on specific stages of floral physiology (i.e. induction, initiation, differentiation and development) compared to more generalized conclusions obtained with growth data alone. The separation of direct and indirect effects on floral physiology is possible with floral architectural analysis.

Citrus are polycarpic and evergreen species that flower once in spring or several times a year depending on the genotype and the climatic conditions. Floral induction is triggered by low temperature and water-deficit stress and occurs 2–3 months before bud sprouting, whereas differentiation takes place at the same time as sprouting. The induced buds develop single flowers or determinate inflorescences, so that vegetative growth is required at the axillary buds to renew the polycarpic habit. The presence of fruits inhibits sprouting and flower induction from nearby axillary buds in the current season. In some species and cultivars, this results in low flowering intensity the following spring, thus giving rise to alternate bearing. A number of key flowering genes act in the leaf ( CiFT3 , CcMADS19 , etc.) or in the bud ( CsLFY , CsTFL1 , etc.) to promote or inhibit both flowering time and reproductive meristem identity in response to these climatic factors, the fruit dominance, or the age of the plant (juvenility). The expression of some of these genes can be modified by gibberellin treatments, which reduce bud sprouting and flowering in adult trees, and constitute the main horticultural technique to control flowering in citrus. This review presents a comprehensive view of all aspects of the flowering process in citrus, converging the research published during the past half century, which focused on plant growth regulators and the nutritional source-sink relationships and guided research toward the study of gene transcription and plant transformation, and the advances made with the development of the tools of molecular biology published during the current century.

Hemerocallis middendorffii (daylily) is a flowering plant widely used in gardens with high ornamental value and application prospect. However, studies on the flowering regulation mechanism of B-class genes in daylily are limited. As members of B-class MADS-box gene family, PISTILLATA ( PI ) and APETALA3 ( AP3 ) genes play key roles in the development of petals and stamens. To better understand the molecular mechanisms of PI and AP3 genes in daylily and verify their function during the flowering process, HmPI and HmAP3 genes were isolated and functionally characterized. Subcellular localization analysis showed that HmPI and HmAP3 are nuclear proteins. Quantitative real-time PCR analysis showed that the highest expression of HmPI gene was observed in stamen of daylily, being 2.46- to 2.74-fold of those in leaf, petal, calyx, and pistil. However, the highest expression of HmAP3 gene was found in the leaf, being 1.65-fold higher than that in pistil, followed by petal. Furthermore, Arabidopsis with overexpression of HmPI and HmAP3 genes exhibited earlier flowering time (3 to 4 and 5 to 6 d advanced, respectively) and varying extents of deformation in floral organs, specifically increased or decreased numbers of petals and stamens, with bicarpels and sepals turning to petals. Yeast two-hybrid experiments showed an interaction between HmPI and HmAP3 proteins, as well as between them and the flowering suppressor TERMINAL FLOWER 1 (TFL1) protein. These results suggested that both HmPI and HmAP3 genes are involved in the construction of floral organ morphology, laying a foundation for further studies on the regulatory mechanism of flower development in daylily.

Cyclocarya paliurus is an important medical plant owing to the diverse bioactive compounds in its leaves. However, the heterodichogamy with female and male functions segregation within protandry (PA) or protogyny (PG) may greatly affect seed quality and its plantations for medicinal use. To speculate on the factor playing the dominant role in regulating heterodichogamy in C. paliurus, based on phenotypic observations, our study performed a multi comparison transcriptome analysis on female and male buds (PG and PA types) using RNA-seq. For the female and male bud comparisons, a total of 6753 differentially expressed genes (DEGs) were detected. In addition, functional analysis revealed that these DEGs were significantly enriched in floral development, hormone, and GA-related pathways. As the dominant hormones responsible for floral differentiation and development, gibberellins (GAs) in floral buds from PG and PA types were quantified using HPLC-MS. Among the tested GAs, GA3 positively regulated the physiological differentiation (S0) and germination (S2) of floral buds. The dynamic changes of GA3 content and floral morphological features were consistent with the expression levels of GA-related genes. Divergences of GA3 contents at S0 triggered the asynchronism of physiological differentiation between male and female buds of intramorphs (PA-M vs. PA-F and PG-F vs. PG-M). A significant difference in GA3 content enlarged this asynchronism at S2. Thus, we speculate that GA3 plays the dominant role in the formation of heterodichogamy in C. paliurus. Meanwhile, the expression patterns of GA-related DEGs, including CPS, KO, GA20ox, GA2OX, GID1, and DELLA genes, which play central roles in regulating flower development, coincided with heterodichogamous characteristics. These results support our speculations well, which should be further confirmed.

Zanthoxylum armatum is a prominent plant for food industries. Its male flowers often occur in gynogenesis plants; however, the potential mechanism remains poorly understood. Herein, a total of 26 floral sex differentiation stages were observed to select four vital phases to reveal key factors by using RNA-seq, phytohormones and carbohydrates investigation. The results showed that a selective abortion of stamen or pistil primordia could result in the floral sex differentiation in Z. armatum . Carbohydrates might collaborate with cytokinin to effect the male floral differentiation, whereas female floral differentiation was involved in SA, GA 1 , and ABA biosynthesis and signal transduction pathways. Meanwhile, these endogenous regulators associated with reproductive growth might be integrated into ABCDE model to regulate the floral organ differentiation in Z. armatum . Furthermore, the 21 crucial candidates were identified in co-expression network, which would contribute to uncovering their roles in floral sex differentiation of Z. armatum in further studies. To the best of our knowledge, this study was the first comprehensive investigation to link floral sex differentiation with multi-level endogenous regulatory factors in Z. armatum . It also provided new insights to explore the regulatory mechanism of floral sex differentiation, which would be benefited to cultivate high-yield varieties in Z. armatum .

The transition from vegetative to reproductive growth is important for controlling the flowering of Lycoris radiata. However, the genetic control of this complex developmental process remains unclear. In this study, 18 shoot apical meristem (SAM) samples were collected from early-, mid- and late-flowering populations during floral bud differentiation. The histological analysis of paraffin sections showed that the floral bud differentiation could be divided into six stages; the differentiation time of the early group was earlier than that of the middle and late groups, and the late group was the latest. In different populations, some important differential genes affecting the flowering time were identified by transcriptome profiles of floral bud differentiation samples. Weighted gene co-expression network analysis (WGCNA) was performed to enrich the gene co-expression modules of diverse flowering time populations (FT) and floral bud differentiation stages (ST). In the MEyellow module, five core hub genes were identified, including CO14, GI, SPL8, SPL9, and SPL15. The correlation network of hub genes showed that they interact with SPLs, AP2, hormone response factors (auxin, gibberellin, ethylene, and abscisic acid), and several transcription factors (MADS-box transcription factor, bHLH, MYB, and NAC3). It suggests the important role of these genes and the complex molecular mechanism of floral bud differentiation and flowering time in L. radiata. These results can preliminarily explain the molecular mechanism of floral bud differentiation and provide new candidate genes for the flowering regulation of Lycoris.

Abstract Members of the genus Paphiopedilum are world-famous for their large, colourful flowers, unique floral morphology and long floral lifespan. Most Paphiopedilum species bloom in spring or autumn. The control of flowering time is of great significance to the commercial production of floral crops, because it affects the sales and prices of flowers. However, the mechanism that regulates when Paphiopedilum species bloom is unclear. In the present study, floral bud initiation and development of P. micranthum (spring-flowering species with one flower per stalk), P. dianthum (autumn-flowering species with multiple flowers per stalk) and P. henryanum (autumn-flowering species with one flower per stalk) were investigated by morphological and anatomical methods. We divided Paphiopedilum floral bud differentiation into six phases: the initiation of differentiation, inflorescence primordium differentiation, flower primordium differentiation, sepal primordium differentiation, petal primordium differentiation and column primordium differentiation. We found that the timing of floral bud differentiation for the three species was synchronized when experiencing the same environment, while the period from initiation to flowering largely differed. In addition, initiation of floral bud differentiation in P. dianthum was earlier at a warmer environment. The difference in flowering time of three species was mainly caused by the duration of floral bud development, rather than the initiation time. The findings were of great significance for the cultivation and flowering regulation of Paphiopedilum species. Members of the genus Paphiopedilum are world-famous for their unique and delicate flowers. Most Paphiopedilum species bloom in spring or autumn, while the mechanism that regulates when Paphiopedilum species bloom is unclear. In this study, we found that the difference in flowering of P. dianthum (autumn-flowering), P. micranthum (spring-flowering) and P. henryanum (autumn-flowering) was mainly caused by the duration of floral bud development, rather than the initiation time. In addition, initiation of floral bud differentiation in P. dianthum was earlier in warmer environments. The findings are of great significance for the cultivation and flowering regulation of Paphiopedilum species.

Background Because the floral induction occurs in many plants when specific environmental conditions are satisfied, most plants bloom and bear fruit during the same season each year. In fig, by contrast, the time interval during which inflorescence (flower bud, fruit) differentiation occurs corresponds to the shoot elongation period. Fig trees thus differ from many species in their reproductive growth characteristics. To date, however, the molecular mechanisms underlying this unorthodox physiology of floral induction and fruit setting in fig trees have not been elucidated. Results We isolated a FLOWERING LOCUS T ( FT ) - like gene from fig and examined its function, characteristics, and expression patterns. The isolated gene, F. carica FT ( FcFT1 ), is single copy in fig and shows the highest similarity at the amino acid level (93.1%) to apple MdFT2 . We sequenced its upstream region (1,644 bp) and identified many light-responsive elements. FcFT1 was mainly expressed in leaves and induced early flowering in transgenic tobacco, suggesting that FcFT1 is a fig FT ortholog. Real-time reverse-transcription PCR analysis revealed that FcFT1 mRNA expression occurred only in leaves at the lower nodes, the early fruit setting positions. mRNA levels remained a constant for approximately 5 months from spring to autumn, corresponding almost exactly to the inflorescence differentiation season. Diurnal variation analysis revealed that FcFT1 mRNA expression increased under relative long-day and short-day conditions, but not under continuous darkness. Conclusion These results suggest that FcFT1 activation is regulated by light conditions and may contribute to fig’s unique fruit-setting characteristics.

Architectural analysis describes the position and fate (vegetative or floral) of plant meristems to account for differences in their sensitivity to stimuli depending on developmental stage and position on the plant. To provide further insight into the flowering responses of long day strawberries to nitrogen, ‘Elan’ seedlings were fertilized in mid-October, overwintered in a greenhouse, then dissected the following March and their floral architecture evaluated. Additional plants from fall N treatments were placed under ND and fertilized weekly for four weeks with 100, 400, 800 or 1200 ppm N during greenhouse-forcing under ND and growth monitored until June. Plants were dissected after forcing and their floral architecture evaluated. Fall fertilized plants were significantly more floral than non-fertilized controls before forcing. Some axillary buds of fertilized plants formed floral branch crowns but there were no floral branch crowns on non-fertilized plants. Precocity was not affected by fall N and 400, 800 or 1200 ppm spring N were equally effective in accelerating flowering (+1 week) compared to 100 ppm spring N. Fall N enhanced the number of inflorescences and flowers produced by the primary crown. Spring N enhanced flowering of branch crowns and the total numbers of inflorescences and flowers per plant. Inflorescence production was a qualitative response to N while flower production was quantitative. Architectural models of post-forcing dissected plants provided additional insight. All 100 ppm spring N terminal meristems were floral while 400 and 800 ppm spring N meristems were less floral. All terminal meristems of plants receiving 100 ppm fall N before 1200 ppm spring N were floral but meristems from plants that did not receive fall N before 1200 ppm spring N were much less floral. Branch crown formation was enhanced with elevated (400, 800 or 1200 ppm) spring N and prior fall N enhanced their floral nature.