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In a genetic screen in a drnl-2 background, we isolated a loss-of-function allele in miR319a (miR319a¹²⁹). Previously, miR319a has been postulated to play a role in leaf development based on the dramatic curled-leaf phenotype of plants that ectopically express miR319a (jaw-D). miR319a¹²⁹ mutants exhibit defects in petal and stamen development; petals are narrow and short, and stamens exhibit defects in anther development. The miR319a¹²⁹ loss-of-function allele contains a single-base change in the middle of the encoded miRNA, which reduces the ability of miR319a to recognize targets. Analysis of the expression patterns of the three members of the miR319 gene family (miR319a, miR319b, and miR319c) indicates that these genes have largely non-overlapping expression patterns suggesting that these genes have distinct developmental functions. miR319a functions by regulating the TCP transcription factors TCP2, TCP3, TCP4, TCP10, and TCP24; the level of RNA expression of these TCP genes is down-regulated in jaw-D and elevated in miR319a¹²⁹. Several lines of evidence demonstrate that TCP4 is a key target of miR319a. First, the tcp4soj⁶ mutant, which contains a mutation in the TCP4 miRNA-binding site complementary to the miR319a¹²⁹ mutation, suppresses the flower phenotype of miR319a¹²⁹. Second, expression of wild-type TCP4 in petals and stamens (i.e., AP3:TCP4) has no effect on flower development; by contrast, a miRNA-resistant version of TCP4, when expressed in petals and stamens (i.e., pAP3:mTCP4) causes these organs not to develop. Surprisingly, when AP3:TCP4 is present in a miR319a¹²⁹ background, petal and stamen development is severely disrupted, suggesting that proper regulation by miR319a of TCP4 is critical in these floral organs.

Unlike animal cells, plant cells do not possess centrosomes that serve as microtubule organizing centers; how microtubule arrays are organized throughout plant morphogenesis remains poorly understood. We report here that Arabidopsis INCREASED PETAL GROWTH ANISOTROPY 1 (IPGA1), a previously uncharacterized microtubuleassociated protein, regulates petal growth and shape by affecting cortical microtubule organization. Through a genetic screen, we showed that IPGA1 loss-of-function mutants displayed a phenotype of longer and narrower petals, as well as increased anisotropic cell expansion of the petal epidermis in the late phases of flower development. Mapbased cloning studies revealed that IPGA1 encodes a previously uncharacterized protein that colocalizes with and directly binds to microtubules. IPGA1 plays a negative role in the organization of cortical microtubules into parallel arrays oriented perpendicular to the axis of cell elongation, with the ipga1-1 mutant displaying increased microtubule ordering in petal abaxial epidermal cells. The IPGA1 family is conserved among land plants and its homologs may have evolved to regulate microtubule organization. Taken together, our findings identify IPGA1 as a novel microtubuleassociated protein and provide significant insights into IPGA1-mediated microtubule organization and petal growth anisotropy.

Background Phalaenopsis orchids, belonging to the Orchidaceae family, one of the largest groups of angiosperms, possess significant commercial value due to their fascinating flowers. Petal size is a vital trait that directly determines flower size and shape of Phalaenopsis . However, the genetic and developmental regulation of petal size in Phalaenopsis remains unexplored. Results In this study, we tracked the petal growth pattern through five stages of flower opening, discovering that cell division stops at stage 2 and stages 3 to 5 are the critical periods of rapid petal expansion. RNA-seq was then conducted to further reveal the molecular mechanisms underlying petal size regulation. Gene ontology (GO) analysis indicated that the differentially expressed genes (DEGs) from the four comparable groups were both enriched in terms related to cell expansion. Endogenous hormone assays showed that auxin, cytokinin, and gibberellin were implicated in the petal growth of Phalaenopsis . Moreover, six auxin signaling pathway genes, 11 cell expansion-related genes, and 30 transcription factors (TFs) identified through trend analysis were abundantly expressed during the critical period of petal expansion, suggesting that they may influence petal size by regulating cell expansion. In contrast, 18 TFs exhibited the highest expression levels at the S1 stage, indicating their potential role in petal cell proliferation. Based on weighted gene co-expression network analysis (WGCNA), six hub genes ( PaLOF2 , PaSWEET11 , PaVNI2 , PaHDA3 , PaPMEI3 , PaXTH30 ) were screened from the green and yellow module which was highly associated with the petal size. Conclusion Our results lay a foundation for further exploration of the molecular mechanisms regulating petal size development and are significant for molecular breeding programs aimed at generating novel Phalaenopsis with desirable traits.

Background The BZR family genes encode plant-specific transcription factors as pivotal regulators of plant BR signaling pathways, critically influencing plant growth and development. Results In this study, we performed a genome-wide investigation of the BZR family gene in gerbera to identify the key components of the BR pathway that may function in petal growth. The identified BZR genes, named GhBEH1-7 ( GhBEH1 , GhBEH2 , GhBEH3 , GhBEH4 , GhBEH5 , GhBEH6 , GhBEH7 ), are distributed across chromosomes 3, 5, 10, 11, 12, 14 and 15. These genes exhibit similar exon–intron structures and possess typical BZR family structures. Phylogenetic analysis clustered these genes into two distinct subgroups. Analysis of cis -acting elements revealed their involvement in hormone response, stress response, and growth regulation. Subcellular localization analysis indicated nuclear localization for GhBEH1 and GhBEH2, while the remaining five genes exhibited dual localization in the nucleus and cytoplasm. The transactivation assay indicated that GhBEH1 and GhBEH2 may function as transcriptional repressors, contrasting with the transcriptional activation observed for the other five genes. Notably, seven GhBEHs exhibit various expression patterns under different growth stages of ray florets and BR treatment conditions. Meanwhile GhBEH1 and GhBEH2 showed pronounced responsiveness to BR stimulation. Conclusion Our work explains genome-wide identification, characterization, and expression analysis of gerbera’s BZR transcription factor family. We hinted that these seven GhBEHs are involved in petal growth and development regulation. These findings provide a basis for further studies on the biological function of the BZR gene family in petal growth and a theoretical basis for future horticultural application in gerbera.

Key message Auxin regulates chrysanthemum petal elongation by promoting cell elongation. Transcriptomic analysis shows that auxin signal transduction may connect with other transcription factors by TCPs to regulate chrysanthemum petal elongation. As an ornamental species, Chrysanthemum morifolium has high ornamental and economic value. Petal size is the primary factor that influences the ornamental value of chrysanthemum, but the mechanism underlying the development of C. morifolium petals remains unclear. In our study, we tracked the growth of petals and found that the basal region of ‘Jinba’ petals showed a higher elongation rate, exhibiting rapid cell elongation during petal growth. During petal elongation growth, auxin was demonstrated to promote cell elongation and an increase in cell numbers in the petal basal region. To further study the molecular mechanisms underlying petal growth, the RNA-seq (high-throughput cDNA sequencing) technique was employed. Four cDNA libraries were assembled from petals in the budding, bud breaking, early blooming and full blooming stages of ‘Jinba’ flower development. Analysis of differentially expressed genes (DEGs) showed that auxin was the most important regulator in controlling petal growth. The TEOSINTEBRANCHED 1, CYCLOIDEA and PCF transcription factor genes ( TCPs ), basic helix-loop-helix- encoding gene ( bHLH ), glutaredoxin-C ( GRXC ) and other zinc finger protein genes exhibited obvious up-regulation and might have significant effects on the growth of ‘Jinba’ petals. Given the interaction between these genes in Arabidopsis thaliana , we speculated that auxin signal transduction might exhibit a close relationship with transcription factors through TCPs. In summary, we present the first comprehensive transcriptomic and hormone analyses of C. morifolium petals. The results offer direction in identifying the mechanism underlying the development of chrysanthemum petals in the elongated phase and have great significance in improving the ornamental characteristics of C. morifolium via molecular breeding.

MicroRNAs (miRNAs) are involved in regulating many aspects of plant growth and development at the post-transcriptional level. Gerbera (Gerbera hybrida) is an important ornamental crop. However, the role of miRNAs in the growth and development of gerbera is still unclear. In this study, we used high-throughput sequencing to analyze the expression profiles of miRNAs in ray floret during inflorescence opening. A total of 164 miRNAs were obtained, comprising 24 conserved miRNAs and 140 novel miRNAs. Ten conserved and 15 novel miRNAs were differentially expressed during ray floret growth, and 607 differentially expressed target genes of these differentially expressed miRNAs were identified using psRNATarget. We performed a comprehensive analysis of the expression profiles of the miRNAs and their targets. The changes in expression of five miRNAs (ghy-miR156, ghy-miR164, ghy-miRn24, ghy-miRn75 and ghy-miRn133) were inversely correlated with the changes in expression of their eight target genes. The miRNA cleavage sites in candidate target gene mRNAs were determined using 5′-RLM-RACE. Several miRNA-mRNA pairs were predicted to regulate ray floret growth and anthocyanin biosynthesis. In conclusion, the results of small RNA sequencing provide valuable information to reveal the mechanisms of miRNA-mediated ray floret growth and anthocyanin accumulation in gerbera.

Petal growth is central to floral morphogenesis, but the underlying genetic basis of petal growth regulation is yet to be elucidated. In this study, we found that the basal region of the ray floret petals of Gerbera hybrida was the most sensitive to treatment with the phytohormones gibberellin (GA) and abscisic acid (ABA), which regulate cell expansion during petal growth in an antagonistic manner. To screen for differentially expressed genes (DEGs) and key regulators with potentially important roles in petal growth regulation by GA or/and ABA, the RNA-seq technique was employed. Differences in global transcription in petals were observed in response to GA and ABA and target genes antagonistically regulated by the two hormones were identified. Moreover, we also identified the pathways associated with the regulation of petal growth after application of either GA or ABA. Genes relating to the antagonistic GA and ABA regulation of petal growth showed distinct patterns, with genes encoding transcription factors (TFs) being active during the early stage (2 h) of treatment, while genes from the \"apoptosis\" and \"cell wall organization\" categories were expressed at later stages (12 h). In summary, we present the first study of global expression patterns of hormone-regulated transcripts in G. hybrida petals; this dataset will be instrumental in revealing the genetic networks that govern petal morphogenesis and provides a new theoretical basis and novel gene resources for ornamental plant breeding.

[...]the mean interruption temperatures showed that 1 day delay in the marketing chain resulted in 1 day (Aster spp. and Gypsophila spp.) to 3 days (Dianthus spp. and Chrysanthemum spp.) decrease in vase life (van Gorsel and Ravesloot,1994). [...]there has been a considerable emphasis and discussion within the floral industry regarding the need of cold-chain, which is a type of supply chain that is temperature-controlled from the point of production, to the transportation stages, storage, distribution processes and finally delivery to the end-user (van der Hulst,2004; Reid and Jiang,2005; Leonard et al.,2011). [...]there is often a lack of cold-chain during logistics, leading to the exposition of flowers to high and fluctuating temperatures. Blue light has also been shown to suppress the development of blue mold (Penicillium italicum) in Citrus unshiu M. and gray mold (Botrytis cinerea) in Solanum lycopersicum L., and at least, these effects could be partially related with the enhanced proline accumulation and antioxidative processes (Kim et al.,2013; Yamaga et al.,2015). Since gray mold caused by Botrytis cinerea is one of the most important diseases of several ornamental flowers including Chrysanthemum spp., Begonia spp., Dahlia spp., Geranium spp., Gerbera spp., Tulipa spp., Rosa hybrida L., and Viola spp. [...]we think light environment control can be a remarkable quality preservation technique, despite that its commercial use is still inadequate compared to existing technologies such as the use of preservatives and cold-chain.

Gerbera hybrida is a cut-flower crop of global importance, and an understanding of the mechanisms underlying petal development is vital for the continued commercial development of this plant species. Brassinosteroids (BRs), a class of phytohormones, are known to play a major role in cell expansion, but their effect on petal growth in G. hybrida is largely unexplored. In this study, we found that the brassinolide (BL), the most active BR, promotes petal growth by lengthening cells in the middle and basal regions of petals, and that this effect on petal growth was greater than that of gibberellin (GA). The RNA-seq (high-throughput cDNA sequencing) technique was employed to investigate the regulatory mechanisms by which BRs control petal growth. A global transcriptome analysis of the response to BRs in petals was conducted and target genes regulated by BR were identified. These differentially expressed genes (DEGs) include various transcription factors (TFs) that were activated during the early stage (0.5 h) of BL treatment, as well as cell wall proteins whose expression was regulated at a late stage (10 h). BR-responsive DEGs are involved in multiple plant hormone signal pathways, hormone biosynthesis and biotic and abiotic stress responses, showing that the regulation of petal growth by BRs is a complex network of processes. Thus, our study provides new insights at the transcriptional level into the molecular mechanisms of BR regulation of petal growth in G. hybrida .

Plant lateral aerial organ (LAO) growth is determined by the number and size of cells comprising the organ. Genetic alteration of one parameter is often accompanied by changes in the other, such that the overall effect on final LAO size is minimized, suggested to be caused by an active organ level ‘compensation mechanism’. For example, the aintegumenta (ant) mutant exhibits reduced cell number but increased cell size in LAOs. The ANT transcription factor regulates the duration of the cell division phase of LAO growth, and its ectopic expression is correlated with increased levels of the cell cycle regulator CYCD3;1. This has previously led to the suggestion that ANT regulates CYCD3;1. It is shown here that while ANT is required for normal cell proliferation in petals, CYCD3;1 is not, suggesting that ANT does not regulate CYCD3;1 during petal growth. Moreover CYCD3;1 expression was similar in wild-type and ant-9 flowers. In contrast to the compensatory changes between cell size and number in ant mutants, cycd3;1 mutants show increased petal cell size unaccompanied by changes in cell number, leading to larger organs. However, loss of CYCD3;1 in the ant-9 mutant background leads to a phenotype consistent with compensation mechanisms. These apparently arbitrary examples of compensation are reconciled through a model of LAO growth in which distinct phases of division and cell expansion occupy differing lengths of a defined overall growth window. This leads to the proposal that many observations of ‘compensation mechanisms’ might alternatively be more simply explained as emergent properties of LAO development.