Expression In Petals Research Articles

EXPANSIN15 is involved in flower and fruit development in Arabidopsis

Key messageEXPANSIN15 is involved in petal cell morphology and size, the fusion of the medial tissues in the gynoecium and expansion of fruit valve cells. It genetically interacts with SPATULA and FRUITFULL.Cell expansion is fundamental for the formation of plant tissues and organs, contributing to their final shape and size during development. To better understand this process in flower and fruit development, we have studied the EXPANSIN15 (EXPA15) gene, which showed expression in petals and in the gynoecium. By analyzing expa15 mutant alleles, we found that EXPA15 is involved in petal shape and size determination, by affecting cell morphology and number. EXPA15 also has a function in fruit size, by affecting cell size and number. Furthermore, EXPA15 promotes fusion of the medial tissues in the gynoecium. In addition, we observed genetic interactions with the transcription factors SPATULA (SPT) and FRUITFULL (FUL) in gynoecium medial tissue fusion, style and stigma development and fruit development in Arabidopsis. These findings contribute to the importance of EXPANSINS in floral and fruit development in Arabidopsis.

Functional identification of anthocyanin glucosyltransferase genes: a Ps3GT catalyzes pelargonidin to pelargonidin 3-O-glucoside painting the vivid red flower color of Paeonia.

Glycosylation from an anthocyanidin 3-O-glucosyltransferase Ps3GT (PsUGT78A27) facilitates the accumulation of pelargonidin 3-O-glucoside, which defines the vivid red flower color and occurs only in specific peony tree cultivars. Although tree peony cultivars of Chinese and Japanese both originated from China, vivid red color is only found in flowers of Japanese cultivars but not of Chinese cultivar groups. In this study, a Japanese tree peony cultivar 'Taiyoh' with vivid red petals and a Chinese tree peony cultivar 'Hu Hong' with reddish pink petals were chosen as the experimental materials. Flavonoids profiling indicated that pelargonidin 3-O-glucoside (Pg3G) detected only in Japanese cultivar contributed to vivid red color of tree peony petals, while pelargonidin 3,5-di-O-glucoside (Pg3G5G) found in both of Japanese and Chinese cultivars was responsible for pink flower color. Through the integration of full-length transcriptome sequencing and in vitro enzymatic activity analysis, two anthocyanin glucosyltransferase genes PsUGT78A27 and PsUGT75L45 were isolated from the petals of tree peony, and their encoding products exhibited enzymatic activities of pelargonidin 3-O-glucosyltransferase and anthocyanin 5-O-glucosyltransferase, respectively. Further quantitative real-time PCR revealed that PsUGT78A27 displayed high expression in petals of both cultivars and PsUGT75L45 was expressed at high levels in cultivar 'Hu Hong' only. Using a gene gun technique, the GFP fusion proteins of PsUGT78A27 and PsUGT75L45 were visualized to be cytoplasmic and nuclear localization in the epidermal cells of tree peony petals, and the glucosylation function of PsUGT78A27 and PsUGT75L45 to alter petal color of tree peony and herbaceous peony had been directly validated in vivo. These results demonstrated that PsUGT78A27 and PsUGT75L45 are key players for the presence or absence of vivid red flower color in tree peony cultivars. Our findings further elucidated the chemical and molecular mechanism of petal pigmentation of Paeonia and could help breed the Paeonia cultivars possessing novel flower colors.

Sequence Characteristics and Expression Analysis of GhCIPK23 Gene in Upland Cotton (Gossypium hirsutum L.).

CIPK (calcineurin B-like-interacting protein kinase) is a kind of serine/threonine protein kinase widely existing in plants, and it plays an important role in plant growth and development and stress response. To better understand the biological functions of the GhCIPK23 gene in upland cotton, the coding sequence (CDS) of the GhCIPK23 gene was cloned in upland cotton, and its protein sequence, evolutionary relationship, subcellular localization, expression pattern and cis-acting elements in the promoter region were analyzed. Our results showed that the full-length CDS of GhCIPK23 was 1368 bp, encoding a protein with 455 amino acids. The molecular weight and isoelectric point of this protein were 50.83 KDa and 8.94, respectively. The GhCIPK23 protein contained a conserved N-terminal protein kinase domain and C-terminal regulatory domain of the CIPK gene family member. Phylogenetic tree analysis demonstrated that GhCIPK23 had a close relationship with AtCIPK23, followed by OsCIPK23, and belonged to Group A with AtCIPK23 and OsCIPK23. The subcellular localization experiment indicated that GhCIPK23 was located in the plasma membrane. Tissue expression analysis showed that GhCIPK23 had the highest expression in petals, followed by sepals, and the lowest in fibers. Stress expression analysis showed that the expression of the GhCIPK23 gene was in response to drought, salt, low-temperature and exogenous abscisic acid (ABA) treatment, and had different expression patterns under different stress conditions. Further cis-acting elements analysis showed that the GhCIPK23 promoter region had cis-acting elements in response to abiotic stress, phytohormones and light. These results established a foundation for understanding the function of GhCIPK23 and breeding varieties with high-stress tolerance in cotton.

Molecular Characterization and Expression Patterns of the HkSVP Gene Reveal Distinct Roles in Inflorescence Structure and Floral Organ Development in Hemerocallis fulva.

SHORT VEGETATIVE PHASE (SVP) genes are members of the well-known MADS-box gene family that play a key role in regulating vital developmental processes in plants. Hemerocallis are perennial herbs that exhibit continuous flowering development and have been extensively used in landscaping. However, there are few reports on the regulatory mechanism of flowering in Hemerocallis. To better understand the molecular basis of floral formation of Hemerocallis, we identified and characterized the SVP-like gene HkSVP from the Hemerocallis cultivar ‘Kanai Sensei’. Quantitative RT-PCR (qRT-PCR) indicated that HkSVP transcript was mainly expressed in the vegetative growth stage and had the highest expression in leaves, low expression in petals, pedicels and fruits, and no expression in pistils. The HkSVP encoded protein was localized in the nucleus of Arabidopsis protoplasts and the nucleus of onion epidermal cells. Yeast two hybrid assay revealed that HKSVP interacted with Hemerocallis AP1 and TFL1. Moreover, overexpression of HkSVP in Arabidopsis resulted in delayed flowering and abnormal phenotypes, including enriched trichomes, increased basal inflorescence branches and inhibition of inflorescence formation. These observations suggest that the HkSVP gene may play an important role in maintaining vegetative growth by participating in the construction of inflorescence structure and the development of flower organs.

An R2R3-MYB transcription factor CmMYB21 represses anthocyanin biosynthesis in color fading petals of chrysanthemum

Flower color is one of the most important traits in ornamental plants. Color fading due to the loss of anthocyanins is a common phenomenon during the flowering process. Here, an R2R3-MYB gene CmMYB21, which was up-regulated in petals during flower color fading process, was isolated from a chrysanthemum cultivar ‘Anastasia Pink’ and functionally characterized. The CmMYB21 protein belonging to subgroup 19, is localized in the nucleus and has no transcriptional activation activity. Additionally, we found that CmMYB21 directly represses CmDFR expression by binding to its promoter. Ectopic over-expression of CmMYB21 in tobacco suppressed anthocyanin accumulation and NtDFR expression in petals. This work suggests that CmMYB21 participates in regulating floral color fading in chrysanthemum by actively suppressing anthocyanin biosynthesis.

Effects of humic acid on antioxidant defense system and senescence-related genes expression in petals of LA-Hybrid Lily

Effects of humic acid on antioxidant defense system and senescence-related genes expression in petals of LA-Hybrid Lily

Endogenous phytosulfokine α (PSKα) signaling delays petals senescence and prolongs vase life of cut rose flowers (Rosa hybrida cv. Angelina)

This study investigated the endogenous phytosulfokine α (PSKα) signaling during opening and senescence in rose flowers. Our results showed that the higher phytosulfokines (PSKs) and tyrosyl protein sulfotransferase (TPST) expression could be responsible for higher endogenous PSKα accumulation in petals during rose flowers opening (stages 2 and 3). By triggering the endogenous PSKα signaling, higher phytosulfokine receptor 1 (PSKR1) expression could be responsible for higher cytosolic cyclic guanosine monophosphate (cGMP) accumulation in petals during rose flowers opening (stages 3 and 4). Higher protein kinase G (PKG) and cyclic nucleotide-gated ion channel 1 (CNGC1) expression accompanying higher plasma membrane intrinsic protein 2 (PIP2) and tonoplast intrinsic protein 1 (TIP1) expression in petals during rose flowers opening may arise from higher cytosolic cGMP accumulation giving rise to higher petals relative water content (RWC) (stage 4). Triggering phosphodiesterase (PDE) expression lay off cytosolic cGMP signaling. Suppressing PKG and CNGC1 expression accompanying lower PIP2 and TIP1 expression accelerates petals senescence in rose flowers representing by deteriorating petals membrane integrity revealed by higher electrolyte leakage and malondialdehyde (MDA) accumulation (stage 5 and 6). For delaying petals senescence and prolonging vase life in cut rose flowers, we employed exogenous PSKα treatment at the commercial harvest stage (stage 3). Our results showed that the suppressing PDE expression in petals by exogenous 150 nM PSKα treatment could be responsible for allowing cytosolic cGMP signaling ongoing for supporting PKG and CNGC1 expression accompanying by higher PIP2 and TIP1 expression. Exogenous 150 nM PSKα treatment, outperforming cut rose flowers by delayed senescence and prolonged vase life to 16 days from 12 days could be ascribed to preserving membrane integrity revealed by lower electrolyte leakage and MDA accumulation. Our results could be proposed that exogenous PSKα treatment and endogenous PSKα signaling for employing in the floriculture industry for delaying petals senescence and prolonging the vase life of cut rose flower.

MYB1 transcription factor regulation through floral scent in Cymbidium cultivar ‘Sael Bit’

Cymbidium belongs to Orchidaceae, one of the most abundant angiosperm families. Cymbidium cultivars have a high aesthetic value and commercially valued characteristics such as a pleasant scent and a variety of flower colors. Cymbidium cultivar ‘Sael Bit’, which was developed by National Institute of Horticultural & Herbal Science (NIHHS), is highly fragrant with small green and light yellow flowers. An analysis of ‘Sael Bit’ floral scent emissions by an electronic nose showed that the petal and initial flowering stage emitted a strong scent. In an headspace-solid phase micro extraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) ‘Sael Bit’ study, we identified alkenes and benzenoids, such as tridecane, benzene, and Z-2-octenal, as major volatile organic compounds. V-myb myeloblastosis viral oncogene homolog (MYB) transcription factors (TFs) play a positive role in floral scent regulation. However, little is known about the MYB transcriptional regulation of floral scent biosynthesis. Due to the importance of the plant’s biology, we need to study the floral scent MYB TFs in this plant. In the present work, we isolated and cloned the full-length cDNA of Cymbidium cultivar ‘Sael Bit’ MYB1 from fully open flower. CsMYB1 encodes an 840-bp open reading frame and 280 amino acids by functional characterization. In q-RT-PCR expression analysis, CsMYB1 TF showed the highest expression in petals and columns compared to sepals and labella. Moreover, this MYB gene expressed various flower developmental stages and was highly expressed at the fully open flower stage. The phenylpropanoid/benzenoid and ester compounds responsible genes expressed through CsMYB1 TF regulation in q-RT-PCR analysis. According to these results, we suggest that CsMYB1 might be involved in the regulation of phenylpropanoid/benzenoid genes in floral scent profile. In future studies, we will focus on develop regulation models of floral scent in Cymbidium cultivar ‘Sael Bit’.

Transcriptome-based analysis of carotenoid accumulation-related gene expression in petals of Chinese cabbage (Brassica rapa L.).

To identify genes associated with carotenoid accumulation in petals of Chinese cabbage, the composition and content of carotenoids were analyzed, and comparative transcriptome sequencing was performed between the yellow flower line, 92S105, and the orange flower line, 94C9. High-performance liquid chromatography (HPLC) revealed that petals of 92S105 were high in violaxanthin as well as lutein, whereas petals of 94C9 showed considerable levels of lutein and β-carotene. Transcriptome analysis showed that 3534 and 3833 genes were up- and down-regulated in 94C9, respectively. Among these differentially expressed genes (DEGs), many related to carotenoid accumulation were identified, including 12 carotenoid biosynthesis pathway genes, 4 transcription factor genes, and 1028 specifically expressed genes. β-carotene hydroxylase 1 (BrBCH1), BrBCH2, zeaxanthin epoxidase (BrZEP), and MYB transcription factor gene (BrGAMYB) were down-regulated in petals of 94C9 when compared with petals of 92S105, which caused β-carotene accumulation and may lead to orange petal color in 94C9. Expression levels of 20 DEGs were verified by qPCR and the results were highly consistent with those of transcriptome sequencing. Moreover, Gene Ontology (GO) enrichment analysis revealed that membrane, binding, and metabolic processes were the most significantly enriched GO terms in cellular component, molecular function, and biological process ontologies, respectively. In conclusion, our study analyzed the differences in composition and content of carotenoids between 92S105 and 94C9 and identified potential candidate genes related to carotenoid accumulation in petals, thereby creating a solid foundation for future studies on the mechanism regulating carotenoid accumulation in petals of Chinese cabbage.

Transcriptome analysis in petals and leaves of chrysanthemums with different chlorophyll levels

BackgroundChlorophylls (Chls) are magnesium-containing tetrapyrrole macromolecules responsible for the green color in plants. The Chl metabolic pathway has been intensively studied and nearly all the enzymes involved in the pathway have been identified and characterized. Synthesis and activity of these enzymes are tightly regulated in tissue- and developmental stage–specific manners. Leaves contain substantial amounts of Chls because Chls are indispensable for photosynthesis. In contrast, petals generally contain only trace amounts of Chls, which if present would mask the bright petal color. Limited information is available about the mechanisms that control such tissue-specific accumulation of Chls.ResultsTo identify the regulatory steps that control Chl accumulation, we compared gene expression in petals and leaves of chrysanthemum cultivars with different Chl levels. Microarray and quantitative real-time PCR analyses showed that the expression levels of Chl biosynthesis genes encoding glutamyl-tRNA reductase, Mg-protoporphyrin IX chelatase, Mg-protoporphyrin IX monomethylester cyclase, and protochlorophyllide oxidoreductase were well associated with Chl content: their expression levels were lower in white petals than in green petals, and were highest in leaves. Among Chl catabolic genes, expression of STAY-GREEN, encoding Mg-dechelatase, which is a key enzyme controlling Chl degradation, was considerably higher in white and green petals than in leaves. We searched for transcription factor genes whose expression was well related to Chl level in petals and leaves and found three such genes encoding MYB113, CONSTANS-like 16, and DREB and EAR motif protein.ConclusionsFrom our transcriptome analysis, we assume that a low rate of Chl biosynthesis and a high rate of Chl degradation lead to the absence of Chls in white chrysanthemum petals. We identified several candidate transcription factors that might affect Chl accumulation in chrysanthemum petals. Functional analysis of these transcription factors will provide a basis for future molecular studies of tissue-specific Chl accumulation.

Genome-wide identification, classification, and analysis of NADP-ME family members from 12 crucifer species.

NADP-dependent malic enzymes (NADP-MEs) play essential roles in both normal development and stress responses in plants. Here, genome-wide analysis was performed to identify 65 putative NADP-ME genes from 12 crucifer species. These NADP-ME genes were grouped into five categories of syntenic orthologous genes and were divided into three clades of a phylogenic tree. Promoter motif analysis showed that NADP-ME1 genes in Group IV were more conserved with each other than the other NADP-ME genes in Groups I and II. A nucleotide motif involved in ABA responses, desiccation and seed development was found in the promoters of most NADP-ME1 genes. Generally, the NADP-ME genes of Brassica rapa, B. oleracea and B. napus had less introns than their corresponding Arabidopsis orthologs. In these three Brassica species, the NADP-ME genes derived from the least fractionated subgenome have lost less introns than those from the medium fractionated and most fractionated subgenomes. BrNADP-ME1 showed the highest expression in petals and mature embryos. Two paralogous NADP-ME2 genes (BrNADP-ME2a and BrNADP-ME2b) shared similar expression profiles and differential expression levels. BrNADP-ME3 showed down-regulation during embryogenesis and reached its lowest expression in early cotyledonary embryos. BrNADP-ME4 was expressed widely in multiple organs and showed high expression during the whole embryogenesis process. Different NADP-ME genes of B. rapa showed differential gene expression profiles in young leaves after ABA treatment or cold stress. Our genome-wide identification and characterization of NADP-ME genes extend our understanding of the evolution or function of this family in Brassicaceae.

Disruption of a CAROTENOID CLEAVAGE DIOXYGENASE 4 gene converts flower colour from white to yellow in Brassica species.

In Brassica napus, yellow petals had a much higher content of carotenoids than white petals present in a small number of lines, with violaxanthin identified as the major carotenoid compound in yellow petals of rapeseed lines. Using positional cloning we identified a carotenoid cleavage dioxygenase 4 gene, BnaC3.CCD4, responsible for the formation of flower colour, with preferential expression in petals of white-flowered B. napus lines. Insertion of a CACTA-like transposable element 1 (TE1) into the coding region of BnaC3.CCD4 had disrupted its expression in yellow-flowered rapeseed lines. α-Ionone was identified as the major volatile apocarotenoid released from white petals but not from yellow petals. We speculate that BnaC3.CCD4 may use δ- and/or α-carotene as substrates. Four variations, including two CACTA-like TEs (alleles M1 and M4) and two insertion/deletions (INDELs, alleles M2 and M3), were identified in yellow-flowered Brassica oleracea lines. The two CACTA-like TEs were also identified in the coding region of BcaC3.CCD4 in Brassica carinata. However, the two INDELs were not detected in B. napus and B. carinata. We demonstrate that the insertions of TEs in BolC3.CCD4 predated the formation of the two allotetraploids.

Molecular cloning of BnZEP and its expression in petals of different colors inBrassica napus L.

C?????arotenoids are a class of pigment elements present in photosynthetic organisms. T??he transcripts of specific carotenoid biosynthetic genes are probably important for the formation of different colors of flower petals. Zeaxanthin epoxidase (ZEP) enzyme activity is important for the high content of carotenoids in petals. In the present study, the zeaxanthin epoxidase gene in Brassica napus L. (BnZEP) was cloned and bioinformatically analyzed. The expression levels of the BnZEP gene in different plant organs and petals of different colors were investigated and compared in B. Napus. The results showed that the full-length cDNA sequence of BnZEP was 2228 bp, containing an open reading frame of 2010 bp and encoding a putative protein of 669 amino acids, with a molecular weight of 73.8 kDa and an isoelectric point (pI) of 6.16. The full-length genomic DNA sequence of BnZEP was 3268 bp, containing 16 exons and 15 introns, the same as in Arabidopsis thaliana (AtZEP). The predicted amino acid sequence of BnZEP revealed a close phylogenetic relationship among the cruciferous species, including Arabidopsis thaliana. The expression levels of BnZEP were remarkably different in different organs and in petals of different colors. Obviously higher expression levels of BnZEP were found in flower petals than in leaves and buds. Yellow petals had markedly higher expression levels of BnZEP than white petals. The results showed that the expression level of BnZEP was positively correlated with yellow petal color in B. Napus L. However, the highest expression level of BnZEP was observed in the pale yellow flower petals of the F1 hybrid (HW243 × ZHONGYOU 821). This implied that the expression level of BnZEP was not completely related to the degree of yellow petal color in B. Napus L. Based on the roles of ZEP enzyme in the xanthophyll cycle, it was suggested that the yellow flower color in Brassica napus L. Was probably associated with the accumulation of antheraxanthin and violaxanthin in the petals. However, further studies are necessary to identify the specific key carotenoid(s) for the yellow color in the petals of Brassica napus L.

An apple B-box protein, MdCOL11, is involved in UV-B- and temperature-induced anthocyanin biosynthesis.

Our studies showed that an apple B-box protein, MdCOL11, the homolog of AtBBX22, is involved in UV-B- and temperature-induced anthocyanin biosynthesis in apple peel. Anthocyanin is responsible for the red pigmentation in apple peel and a R2R3 MYB gene, MdMYBA/1/10, a homolog of MdMYBA, controls its accumulation. Arabidopsis PAP1 is under the control of a series of upstream factors involved in light signal transduction and photomorphogenesis, such as ELONGATED HYPOCOTYL 5 (HY5) and B-box family (BBX) proteins. In this study, we identified and characterized the homolog of Arabidopsis BBX22 in apple, designated as MdCOL11. Overexpression of MdCOL11 in Arabidopsis enhanced the accumulation of anthocyanin. In apples, MdCOL11 was differentially expressed in all tissues, with the highest expression in petals and the lowest expression in the xylem. Transcripts of MdCOL11 noticeably accumulated at the ripening stage, concomitant with increases in the expressions of anthocyanin biosynthesis-related genes. In an in vitro treatment experiment, MdCOL11 was upregulated in an ultra-violet (UV)-B- and temperature-dependent manner, together with the inductions of anthocyanin biosynthesis-related genes and anthocyanin accumulation in apple peel. Furthermore, a dual-luciferase assay indicated that (1) MdCOL11 regulated the expression of MdMYBA and (2) MdCOL11 was a target of MdHY5. Taken together, our results suggest that MdCOL11 is involved in MdHY5-mediated signal transduction and regulates anthocyanin accumulation in apple peel, which sheds new light on anthocyanin accumulation in apples.

RhHB1 mediates the antagonism of gibberellins to ABA and ethylene during rose (Rosa hybrida) petal senescence

Rose (Rosa hybrida) is one of the most important ornamental plants worldwide; however, senescence of its petals terminates the ornamental value of the flower, resulting in major economic loss. It is known that the hormones abscisic acid (ABA) and ethylene promote petal senescence, while gibberellins (GAs) delay the process. However, the molecular mechanisms underlying the antagonistic effects amongst plant hormones during petal senescence are still unclear. Here we isolated RhHB1, a homeodomain-leucine zipper I transcription factor gene, from rose flowers. Quantitative RT-PCR and GUS reporter analyses showed that RhHB1 was strongly expressed in senescing petals, and its expression was induced by ABA or ethylene in petals. ABA or ethylene treatment clearly accelerated rose petal senescence, while application of the gibberellin GA3 delayed the process. However, silencing of RhHB1 delayed the ABA- or ethylene-mediated senescence, and resulted in higher petal anthocyanin levels and lower expression of RhSAG12. Moreover, treatment with paclobutrazol, an inhibitor of GA biosynthesis, repressed these delays. In addition, silencing of RhHB1 blocked the ABA- or ethylene-induced reduction in expression of the GA20 oxidase encoded by RhGA20ox1, a gene in the GA biosynthetic pathway. Furthermore, RhHB1 directly binds to the RhGA20ox1 promoter, and silencing of RhGA20ox1 promoted petal senescence. Eight senescence-related genes showed substantial differences in expression in petals after treatment with GA3 or paclobutrazol. These results suggest that RhHB1 mediates the antagonistic effect of GAs on ABA and ethylene during rose petal senescence, and that the promotion of petal senescence by ABA or ethylene operates through an RhHB1-RhGA20ox1 regulatory checkpoint.

Expression of an AtNAP gene homolog in senescing morning glory (Ipomoea nil) petals of two cultivars with a different flower life span

AtNAP, a NAC family transcription factor, has been shown to promote leaf senescence in Arabidopsis. We isolated an AtNAP homolog in morning glory (Ipomoea nil), designated InNAP, and investigated its expression during petal senescence. We used two cultivars, one showing a normal short flower life span (cv. Peking Tendan) and another a longer life span (cv. Violet). InNAP was highly expressed in both cultivars. Expression was high before that of the senescence marker gene InSAG12. InNAP and InSAG12 expression was high in cv. Peking Tendan before cv. Violet. The expression of both genes was therefore temporally related to the onset of the visible senescence symptoms. An inhibitor of ethylene action (silver thiosulphate, STS) delayed petal senescence in cv. Peking Tendan but had no effect in cv. Violet. STS treatment had no clear effect on the InNAP expression in petals of both cultivars, suggesting that endogenous ethylene may not be necessary for its induction. These data suggest the hypothesis that InNAP plays a role in petal senescence, independent of the role of endogenous ethylene.

RhNAC3, a stress‐associated NAC transcription factor, has a role in dehydration tolerance through regulating osmotic stress‐related genes in rose petals

Petal cell expansion depends on cell wall metabolism, changes in cell turgor pressure and restructuring of the cytoskeleton, and recovery ability of petal cell expansion is defined as an indicator of dehydration tolerance in flowers. We previously reported that RhNAC2, a development-related NAC domain transcription factor, confers dehydration tolerance through regulating cell wall-related genes in rose petals. Here, we identify RhNAC3, a novel rose SNAC gene, and its expression in petals induced by dehydration, wounding, exogenous ethylene and abscisic acid (ABA). Expression studies in Arabidopsis protoplasts and yeast show that RhNAC3 has transactivation activity along its full length and in the carboxyl-terminal domain. Silencing RhNAC3 in rose petals by virus-induced gene silencing (VIGS) significantly decreased the cell expansion of rose petals under rehydration conditions. In total, 24 of 27 osmotic stress-related genes were down-regulated in RhNAC3-silenced rose petals, while only 4 of 22 cell expansion-related genes were down-regulated. Overexpression of RhNAC3 in Arabidopsis gave improved drought tolerance, with lower water loss of leaves in transgenic plants. Arabidopsis ATH1 microarray analysis showed that RhNAC3 regulated the expression of stress-responsive genes in overexpressing lines, and further analysis revealed that most of the RhNAC3-up-regulated genes were involved in the response to osmotic stress. Comparative analysis revealed that different transcription regulation existed between RhNAC3 and RhNAC2. Taken together, these data indicate that RhNAC3, as a positive regulator, confers dehydration tolerance of rose petals mainly through regulating osmotic adjustment-associated genes.

The promoter of the carotenoid cleavage dioxygenase 4a-5 gene of Chrysanthemum morifolium (CmCCD4a-5) drives petal-specific transcription of a conjugated gene in the developing flower

Carotenoids comprise one of the major groups of pigments in flowers. Because carotenoids are physiologically indispensable pigments for all photosynthetic plants, their catabolism must be discretely regulated in photosynthetic organs and non-photosynthetic organs such as petals or fruits. In the chrysanthemum, carotenoid cleavage dioxygenase 4a (CmCCD4a), which is dominantly expressed in petals, cleaves carotenoid, leading to a white flower. CmCCD4a-5 was recently identified as a new member of the CmCCD4a family, but its detailed expression profile in plant tissues has not yet been established. In this study, we sequenced a 1094-bp region upstream of CmCCD4a-5 and assessed its petal-specific promoter activity. To evaluate the activity of this gene, we constructed two types of transgenic Arabidopsis thaliana that possessed, respectively, a fusion gene of a 1090-bp or 505-bp segment of the upstream region plus the β-d-glucuronidase (GUS) gene (1090bUR::GUS and 505bUR::GUS). GUS activity in the 505bUR::GUS strain was observed mainly in the anthers/pollen in flower buds, whereas GUS activity of the 1090bUR::GUS strain was observed in immature petals of the flower buds. Among the cis-acting elements located between positions −505 and −1090, no elements that have previously been reported to enhance the expression in petals or to suppress it in anthers/pollen were detected by PLACE analysis, indicating the existence of unknown cis-element(s). A semiquantitative reverse transcription-polymerase chain reaction analysis revealed that CmCCD4a-5 transcription was prominent in petals but was undetectable in roots, stems and leaves.

A regulatory network for coordinated flower maturation.

For self-pollinating plants to reproduce, male and female organ development must be coordinated as flowers mature. The Arabidopsis transcription factors AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 regulate this complex process by promoting petal expansion, stamen filament elongation, anther dehiscence, and gynoecium maturation, thereby ensuring that pollen released from the anthers is deposited on the stigma of a receptive gynoecium. ARF6 and ARF8 induce jasmonate production, which in turn triggers expression of MYB21 and MYB24, encoding R2R3 MYB transcription factors that promote petal and stamen growth. To understand the dynamics of this flower maturation regulatory network, we have characterized morphological, chemical, and global gene expression phenotypes of arf, myb, and jasmonate pathway mutant flowers. We found that MYB21 and MYB24 promoted not only petal and stamen development but also gynoecium growth. As well as regulating reproductive competence, both the ARF and MYB factors promoted nectary development or function and volatile sesquiterpene production, which may attract insect pollinators and/or repel pathogens. Mutants lacking jasmonate synthesis or response had decreased MYB21 expression and stamen and petal growth at the stage when flowers normally open, but had increased MYB21 expression in petals of older flowers, resulting in renewed and persistent petal expansion at later stages. Both auxin response and jasmonate synthesis promoted positive feedbacks that may ensure rapid petal and stamen growth as flowers open. MYB21 also fed back negatively on expression of jasmonate biosynthesis pathway genes to decrease flower jasmonate level, which correlated with termination of growth after flowers have opened. These dynamic feedbacks may promote timely, coordinated, and transient growth of flower organs.

Arctic Mustard Flower Color Polymorphism Controlled by Petal-Specific Downregulation at the Threshold of the Anthocyanin Biosynthetic Pathway

Intra- and interspecific variation in flower color is a hallmark of angiosperm diversity. The evolutionary forces underlying the variety of flower colors can be nearly as diverse as the colors themselves. In addition to pollinator preferences, non-pollinator agents of selection can have a major influence on the evolution of flower color polymorphisms, especially when the pigments in question are also expressed in vegetative tissues. In such cases, identifying the target(s) of selection starts with determining the biochemical and molecular basis for the flower color variation and examining any pleiotropic effects manifested in vegetative tissues. Herein, we describe a widespread purple-white flower color polymorphism in the mustard Parrya nudicaulis spanning Alaska. The frequency of white-flowered individuals increases with increasing growing-season temperature, consistent with the role of anthocyanin pigments in stress tolerance. White petals fail to produce the stress responsive flavonoid intermediates in the anthocyanin biosynthetic pathway (ABP), suggesting an early pathway blockage. Petal cDNA sequences did not reveal blockages in any of the eight enzyme-coding genes in white-flowered individuals, nor any color differentiating SNPs. A qRT-PCR analysis of white petals identified a 24-fold reduction in chalcone synthase (CHS) at the threshold of the ABP, but no change in CHS expression in leaves and sepals. This arctic species has avoided the deleterious effects associated with the loss of flavonoid intermediates in vegetative tissues by decoupling CHS expression in petals and leaves, yet the correlation of flower color and climate suggests that the loss of flavonoids in the petals alone may affect the tolerance of white-flowered individuals to colder environments.