Base Of Petals Research Articles

Integrative Metabolomic and Transcriptomic Analyses Reveal the Mechanism of Petal Blotch Formation in Rosa persica.

Petal blotch is a specific flower color pattern commonly found in angiosperm families. In particular, Rosa persica is characterized by dark red blotches at the base of yellow petals. Modern rose cultivars with blotches inherited the blotch trait from R. persica. Therefore, understanding the mechanism for blotch formation is crucial for breeding rose cultivars with various color patterns. In this study, the metabolites and genes responsible for the blotch formation in R. persica were identified for the first time through metabolomic and transcriptomic analyses using LC-MS/MS and RNA-seq. A total of 157 flavonoids were identified, with 7 anthocyanins as the major flavonoids, namely, cyanidin 3-O-(6″-O-malonyl) glucoside 5-O-glucoside, cyanidin-3-O-glucoside, cyanidin 3-O-galactoside, cyanidin O-rutinoside-O-malonylglucoside, pelargonidin 3-O-glucoside, pelargonidin 3,5-O-diglucoside, and peonidin O-rutinoside-O-malonylglucoside, contributing to pigmentation and color darkening in the blotch parts of R. persica, whereas carotenoids predominantly influenced the color formation of non-blotch parts. Zeaxanthin and antheraxanthin mainly contributed to the yellow color formation of petals at the semi-open and full bloom stages. The expression levels of two 4-coumarate: CoA ligase genes (Rbe014123 and Rbe028518), the dihydroflavonol 4-reductase gene (Rbe013916), the anthocyanidin synthase gene (Rbe016466), and UDP-flavonoid glucosyltransferase gene (Rbe026328) indicated that they might be the key structural genes affecting the formation and color of petal blotch. Correlation analysis combined with weighted gene co-expression network analysis (WGCNA) further characterized 10 transcription factors (TFs). These TFs might participate in the regulation of anthocyanin accumulation in the blotch parts of petals by modulating one or more structural genes. Our results elucidate the compounds and molecular mechanisms underlying petal blotch formation in R. persica and provide valuable candidate genes for the future genetic improvement of rose cultivars with novel flower color patterns.

Petal abscission is promoted by jasmonic acid-induced autophagy at Arabidopsis petal bases

In angiosperms, the transition from floral-organ maintenance to abscission determines reproductive success and seed dispersion. For petal abscission, cell-fate decisions specifically at the petal-cell base are more important than organ-level senescence or cell death in petals. However, how this transition is regulated remains unclear. Here, we identify a jasmonic acid (JA)-regulated chromatin-state switch at the base of Arabidopsis petals that directs local cell-fate determination via autophagy. During petal maintenance, co-repressors of JA signaling accumulate at the base of petals to block MYC activity, leading to lower levels of ROS. JA acts as an airborne signaling molecule transmitted from stamens to petals, accumulating primarily in petal bases to trigger chromatin remodeling. This allows MYC transcription factors to promote chromatin accessibility for downstream targets, including NAC DOMAIN-CONTAINING PROTEIN102 (ANAC102). ANAC102 accumulates specifically at the petal base prior to abscission and triggers ROS accumulation and cell death via AUTOPHAGY-RELATED GENEs induction. Developmentally induced autophagy at the petal base causes maturation, vacuolar delivery, and breakdown of autophagosomes for terminal cell differentiation. Dynamic changes in vesicles and cytoplasmic components in the vacuole occur in many plants, suggesting JA–NAC-mediated local cell-fate determination by autophagy may be conserved in angiosperms.

Morphological Characterization and Genetic Variability Study on Early Maturing Pigeonpea [Cajanus cajan (L.) Millsp.] Lines

Background: Pigeonpea [Cajanus cajan (L.) Millsp. (2n=22)] is the second most important pulse crop in India after chickpea. In the present study, two-hundred early maturing (less than 140 days) pigeonpea germplasm accessions were evaluated for their genetic parameters based on morphological characters and were subsequently characterized as per the DUS descriptors for pigeonpea. Genetic variability of the population was assessed through genetic parameters and character association analysis. Methods: The plant material comprised of 193 pigeonpea genotypes along with seven checks and the experiment was conducted during kharif 2020-21 and 2021-22 in augmented design. Result: The twenty-one DUS characters were recorded at different crop growth stages. Out of those, the characters for plant height, branching pattern, time to 50% flowering, colour of base of petal, pattern of streaks on petal, pod colour, pod number of seeds, seed colour, seed colour pattern, seed shape and seed size exhibited variation across the accessions. The analysis of variance was executed for the eight different biometrical characters. The highest GCV and PCV value was obtained for the character seed yield per plant (19.91 and 21.4 respectively). Almost all the yield attributing characters except plant height showed high heritability indicating that selection for the characters for crop improvement would be highly effective. Highest genetic advance was observed for the trait pods per plant (42.34) and highest genetic advance as percent of mean was obtained for seed yield per plant (38.24). Correlation analysis among the characters for yield revealed that high positive correlation existed between seed yield per plant with pods per plant (0.580). The character for PH also showed high correlation with seed yield (0.185) which is indicative that high pods per plant and tall plant character contribute significantly towards yield enhancement.

Two New species of Impatiens (Balsaminaceae) from Myanmar

Impatiens yinyinkyii M.M.Latt, B.B.Park & Nob.Tanaka and I. horizontalis M.M.Latt, B.B.Park & Nob.Tanaka (Balsaminaceae) are described and illustrated. Those new species were discovered in Htamanthi Wildlife Sanctuary, northwestern Myanmar. Description, photographic data as well as the comparative characters with their similar species are provided. Impatiens yinyinkyii is similar to I. masonii Hook.f., but differs in having three dark purple blotches in center of flower, specifically at base of dorsal and upper petals of united petals. Impatiens horizontalis resembles I. stenantha Hook.f., I. prostrata Hook. f., I. repens Moon, I. procumbens Franch and I. reptans Hook. f. in having larger, glabrous and elliptic to lanceolate leaves, serrate margin with antrorse bristles, deeply bucciniform lower sepal, twisted spur with abruptly capitate tip, linear ovary, spheroid seed and finally uncommon conspicuous stout stem which is horizontally creeping.

Characterization of Cyclamen genotypes using morphological descriptors and DNA molecular markers in a multivariate analysis.

Morphological and molecular characterization of germplasm is essential for the improvement of cultivated plants efforts. This study investigated the genetic diversity of 32 Cyclamen genotypes comprising 16C. persicum varieties and 16 Cyclamen species using multivariate analysis for 36 morphological traits (19 quantitative and 17 qualitative) and molecular characterization (SRAP and SCoT markers). The color CIELab parameters were collected via PCE-CSM7 that separately measured the leaves dark and silvery patterns and the flower's slip (region of the petal top), eye (the region of the petal base) and sepal. Genetic diversity was also evaluated using Shannon Wiener (H') and Simpson's (λ) Indices, and Pilou evenness (J) using the library vegan from R software. According to the principal component analysis, the variables that contributed the most were leaf pattern color, leaf abaxial surface color, pedicel coiling, leaf and stem number. The color indicators of Cyclamen leaves showed decreased L* values in darker colored genotypes, whereas increased a* values were noticed in flower eye and lower in slip. Molecular characterization was based on 26 SRAP and 12 SCoT markers that produced clearly repeatable DNA bands and exhibited significant levels of polymorphism. Based on the morphological traits and molecular markers data, the UPGMA method for hierarchical clustering technique was used to generate the dendrograms, and their entanglement was obtained using the Tanglegram algorithm from the dendextend package with the R software. Entanglement analysis (0.30) between dendrograms obtained from the morphological and genetic analysis using SRAP markers showed a high association. Comparison between color measurements of flowers (entanglement=0.45) and leaves (entanglement=0.47) with SCoT analysis revealed differences at species level, discriminating between similar genotypes. Combined phenotypic and molecular analysis improved the comprehensive estimation of real diversity in the investigated Cyclamen genotypes. The findings of the present study are useful for quantifying diversity and genetic variability in Cyclamen breeding and genetic investigations.

Metabolic profile and transcriptome reveal the mystery of petal blotch formation in rose

BackgroundPetal blotch is a unique ornamental trait in angiosperm families, and blotch in rose petal is rare and has great esthetic value. However, the cause of the formation of petal blotch in rose is still unclear. The influence of key enzyme genes and regulatory genes in the pigment synthesis pathways needs to be explored and clarified.ResultsIn this study, the rose cultivar ‘Sunset Babylon Eyes’ with rose-red to dark red blotch at the base of petal was selected as the experimental material. The HPLC-DAD and UPLC-TQ-MS analyses indicated that only cyanidin 3,5-O-diglucoside (Cy3G5G) contributed to the blotch pigmentation of ‘Sunset Babylon Eyes’, and the amounts of Cy3G5G varied at different developmental stages. Only flavonols but no flavone were found in blotch and non-blotch parts. As a consequence, kaempferol and its derivatives as well as quercetin and its derivatives may act as background colors during flower developmental stages. Despite of the differences in composition, the total content of carotenoids in blotch and non-blotch parts were similar, and carotenoids may just make the petals show a brighter color. Transcriptomic data, quantitative real-time PCR and promoter sequence analyses indicated that RC7G0058400 (F3’H), RC6G0470600 (DFR) and RC7G0212200 (ANS) may be the key enzyme genes for the early formation and color deepening of blotch at later stages. As for two transcription factor, RC7G0019000 (MYB) and RC1G0363600 (WRKY) may bind to the promoters of critical enzyme genes, or RC1G0363600 (WRKY) may bind to the promoter of RC7G0019000 (MYB) to activate the anthocyanin accumulation in blotch parts of ‘Sunset Babylon Eyes’.ConclusionsOur findings provide a theoretical basis for the understanding of the chemical and molecular mechanism for the formation of petal blotch in rose.

Tree peony PsMYB44 negatively regulates petal blotch distribution by inhibiting dihydroflavonol-4-reductase gene expression.

The tree peony (Paeonia suffruticosa Andr.) has been widely cultivated as a field plant, and petal blotch is one of its important traits, which not only promotes proliferation but also confers high ornamental value. However, the regulatory network controlling blotch formation remains elusive owing to the functional differences and limited conservation of transcriptional regulators in dicots. We performed phylogenetic analysis to identify MYB44-like transcription factors in P. suffruticosa blotched cultivar 'High noon' petals. A candidate MYB44-like transcription factor, PsMYB44, was analysed via expression pattern analysis, subcellular localization, target gene identification, gene silencing in P. suffruticosa petals and heterologous overexpression in tobacco. A blotch formation-related MYB44-like transcription factor, PsMYB44, was cloned. The C-terminal of the PsMYB44 amino acid sequence had a complete C2 motif that affects anthocyanin biosynthesis, and PsMYB44 was clustered in the MYB44-like transcriptional repressor branch. PsMYB44 was located in the nucleus, and its spatial and temporal expression patterns were negatively correlated with blotch formation. Furthermore, a yeast one-hybrid assay showed that PsMYB44 could target the promoter of the late anthocyanin biosynthesis-related dihydroflavonol-4-reductase (DFR) gene, and a dual-luciferase assay demonstrated that PsMYB44 could repress PsDFR promoter activity. On the one hand, overexpression of PsMYB44 significantly faded the red colour of tobacco flowers and decreased the anthocyanin content by 42.3 % by downregulating the expression level of the tobacco NtDFR gene. On the other hand, PsMYB44-silenced P. suffruticosa petals had a redder blotch colour, which was attributed to the fact that silencing PsMYB44 redirected metabolic flux to the anthocyanin biosynthesis branch, thereby promoting more anthocyanin accumulation in the petal base. These results demonstrated that PsMYB44 negatively regulated the biosynthesis of anthocyanin by directly binding to the PsDFR promoter and subsequently inhibiting blotch formation, which helped to elucidate the molecular regulatory network of anthocyanin-mediated blotch formation in plants.

Comparative Metabolome and Transcriptome Analysis of Anthocyanin Biosynthesis in White and Pink Petals of Cotton (Gossypium hirsutum L.).

Upland cotton (Gossypium hirsutum L.) is one of the important fiber crops. Cotton flowers usually appear white (or cream-colored) without colored spots at the petal base, and turn pink on the next day after flowering. In this study, using a mutant showing pink petals with crimson spots at their base, we conducted comparative metabolome and transcriptome analyses to investigate the molecular mechanism of coloration in cotton flowers. Metabolic profiling showed that cyanidin-3-O-glucoside and glycosidic derivatives of pelargonidins and peonidins are the main pigments responsible for the coloration of the pink petals of the mutant. A total of 2443 genes differentially expressed (DEGs) between the white and pink petals were identified by RNA-sequencing. Many DEGs are structural genes and regulatory genes of the anthocyanin biosynthesis pathway. Among them, MYB21, UGT88F3, GSTF12, and VPS32.3 showed significant association with the accumulation of cyanidin-3-O-glucoside in the pink petals. Taken together, our study preliminarily revealed the metabolites responsible for the pink petals and the key genes regulating the biosynthesis and accumulation of anthocyanins in the pink petals. The results provide new insights into the biochemical and molecular mechanism underlying anthocyanin biosynthesis in upland cotton.

PrMYB5 activates anthocyanin biosynthetic PrDFR to promote the distinct pigmentation pattern in the petal of Paeonia rockii.

Paeonia rockii is well-known for its distinctive large dark-purple spot at the white petal base and has been considered to be the main genetic source of spotted tree peony cultivars. In this study, the petal base and petal background of Paeonia ostii (pure white petals without any spot), P. rockii, and other three tree peony cultivars were sampled at four blooming stages from the small bell-like bud stage to the initial blooming stage. There is a distinct difference between the pigmentation processes of spots and petal backgrounds; the spot pigmentation was about 10 days earlier than the petal background. Moreover, the cyanin and peonidin type anthocyanin accumulation at the petal base mainly contributed to the petal spot formation. Then, we identified a C1 subgroup R2R3-MYB transcription factor, PrMYB5, predominantly transcribing at the petal base. This is extremely consistent with PrDFR and PrANS expression, the contents of anthocyanins, and spot formation. Furthermore, PrMYB5 could bind to and activate the promoter of PrDFR in yeast one-hybrid and dual-luciferase assays, which was further verified in overexpression of PrMYB5 in tobacco and PrMYB5-silenced petals of P. rockii by comparing the color change, anthocyanin contents, and gene expression. In summary, these results shed light on the mechanism of petal spot formation in P. rockii and speed up the molecular breeding process of tree peony cultivars with novel spot pigmentation patterns.

Characterization of pigeonpea germplasm using DUS descriptors

The present study was carried out on sixty-eight early duration pigeonpea genotypes during rabi, 2021-22. Twenty traits were recorded as per the descriptors provided by PPV & FRA and several genotypes possessed unique traits that aid in genotype identification and varietal purification. The traits viz., branching pattern, growth habit, stem colour, colour of base of petal, pattern of streaks on petal (standard), pod colour, pod surface stickiness, pod size, the number of seeds per pod, seed colour, seed shape, seed pattern and seed size showed significant variation among genotypes. Characters such as leaf shape, leaf pubescence, days to 50% flowering and pod constriction showed no variation. Sixty-eight genotypes were subjected to cluster analysis and the genotypes were grouped into eight major clusters, where cluster II was the largest one followed by clusters VI, I, IV, V, VII, VIII and III. The genotypes present in different clusters showed high variation for different traits and will be utilized for crop improvement programs. Keywords: Pigeonpea, Distinctiveness, Uniformity, Stability, qualitative, clustering

Increasing floral visitation and hybrid seed production mediated by beauty mark in Gossypium hirsutum.

SummaryHybrid crop varieties have been repeatedly demonstrated to produce significantly higher yields than their parental lines; however, the low efficiency and high cost of hybrid seed production has limited the broad exploitation of heterosis for cotton production. One option for increasing the yield of hybrid seed is to improve pollination efficiency by insect pollinators. Here, we report the molecular cloning and characterization of a semidominant gene, Beauty Mark (BM), which controls purple spot formation at the base of flower petals in the cultivated tetraploid cotton species Gossypium barbadense. BM encodes an R2R3 MYB113 transcription factor, and we demonstrate that GbBM directly targets the promoter of four flavonoid biosynthesis genes to positively regulate petal spot development. Introgression of a GbBM allele into G. hirsutum by marker‐assisted selection restored petal spot formation, which significantly increased the frequency of honeybee visits in G. hirsutum. Moreover, field tests confirmed that cotton seed yield was significantly improved in a three‐line hybrid production system that incorporated the GbBM allele. Our study thus provides a basis for the potentially broad application of this gene in improving the long‐standing problem of low seed production in elite cotton hybrid lines.

Structure and functions of the glandular trichomes in three Arnica species (Asteraceae), depending on their location on leaves and flowers

The aim of this study was to characterize the structural and histochemical features of the glandular trichomes (GTs) of two types localized on the leaves and flowers in three Arnica species. GTs of the first type are found on leaves, peduncle, calyx, ovary, and petal base. They are biseriate, have a cylindrical form and 5 to 9 cell layers. GTs of the second type are located on the peduncle and calyx; they have a biseriate head of two to four cell layers and a long stalk. In each Arnica species differences between GTs of two types include dimensions, intensity of coloration by histochemical dyes, as well as ultrastructural features of the cells. According to the results of fluorescence microscopy and histochemical tests, phenols, terpenes, sesquiterpene lactones and polysaccharides are revealed in all GTs of the studied species; at the same time, the amount and composition of primary and secondary compounds are specific for trichomes of each organ. In the leaf GTs, phenols and terpenes prevail; in the GTs of the first type situated on the peduncle and calyx, acid polysaccharides are met in larger amount then in trichomes of other organs; in the GTs of the second type, sesquiterpene lactones are the main metabolites. At the secretory stage, the apical cells of GTs contain smooth and rough endoplasmic reticulum, diversiform leucoplasts with black inclusions in lamellae, chloroplasts, mitochondria, and Golgi apparatus. A single subcuticular cavity is formed in GTs of the first type, unlike GTs of the second type, where many small subcuticular cavities appear. In these GTs, the head surface looks porous. Although there are structural modifications between trichomes of the same type in different species of Arnica, the functional variations between trichomes of the different types are more significant.

A new variety of Geranium ocellatum (Geraniaceae) from Uttarakhand, India

A new variety, Geranium ocellatum var. albiflorum, is described here from Tehri district of Uttarakhand state, India. The new variety is readily distinguished from G. ocellatum var. ocellatum by its central white spot at the petal base, dichasial inflorescence and peduncle length. A detailed description, photographs and conservation status are provided for the new variety. A key to the varieties of G. ocellatum is also provided.

Morphological Characterization of Okra {Abelmoschus eculentus (L.) Moench} Genotypes

The present study entitled “Morphological characterization of okra {Abelmoschus esculentus (L.) Moench} genotypes” was carried out at the Research farm of Department of Vegetable Science, CCS HAU, Hisar during spring summer season of the year 2012 on the basis of morphological descriptors with the objective to identify key diagnostic characters of the genotypes. Observations were recorded for 14 morphological characters. Analysis of variance studies indicated significant differences among all the genotypes for all the characters under study. Highest mean fruit yield per plant was recorded for the genotype Hisar Naveen. Serration of leaf blade margin, vein colour, intensity of colour between vein, depth of lobing and petal base colour distinguished all the 20 genotypes by assigning them key diagnostic features that would certainly help the plant breeders, to use these diagnostic characters for trait specific use in breeding programme. The genotype Hisar Naveen was found as superior with high mean values for internodal length, number of nodes at first flowering, petiole length, plant height and flower diameter were recorded maximum in HBT-1-1, HBT-51-1-1, HBT-70-1 and HBT-6-7-1 respectively.

Molecular framework underlying floral bilateral symmetry and nectar spur development in Tropaeolum, an atypical member of the Brassicales.

Floral spurs are key innovations associated with elaborate pollination mechanisms that have evolved independently several times across angiosperms. Spur formation can shift the floral symmetry from radial to bilateral, as it is the case in Tropaeolum, the only member of the Brassicales with floral nectar spurs. The genetic mechanisms underlying both spur and bilateral symmetry in the family have not yet been investigated. We studied flower development and morphoanatomy of Tropaeolum longifolium. We also generated a reference transcriptome and isolated all candidate genes involved in adaxial-abaxial differential growth during spur formation. Finally, we evaluated the evolution of the targeted genes across Brassicales and examined their expression in dissected floral parts. Five sepals initiate spirally, followed by five petals alternate to the sepals, five antesepalous stamens, three antepetalous stamens, and three carpels. Intercalary growth at the common base of sepals and petals forms a floral tube. The spur is an outgrowth from the adaxial region of the tube, lined up with the medial sepal. We identified Tropaeolum specific duplications in the TCP3/4L and STM gene lineages, which are critical for spur formation in other taxa. In addition, we found that TM6 (MADS-box), RL2 (RAD-like7), and KN2/6L2 and OSH6L (KNOX1 genes), have been lost in core Brassicales but retained in Tropaeolum. Three genes are pivotal during the extreme adaxial-abaxial asymmetry of the floral tube, namely, TlTCP4L2 restricted to the adaxial side where the spur is formed, and TlTCP12 and TlSTM1 to the abaxial side, lacking a spur.

Spatial patterning of scent in petunia corolla is discriminated by bees and involves the ABCG1 transporter.

Floral guides are patterned cues that direct the pollinator to the plant reproductive organs. The spatial distribution of showy visual and olfactory traits allows efficient plant-pollinator interactions. Data on the mechanisms underlying floral volatile patterns or their interactions with pollinators are lacking. Here we characterize the spatial emission patterns of volatiles from the corolla of the model plant Petunia×hybrida and reveal the ability of honeybees to distinguish these patterns. Along the adaxial epidermis, in correlation with cell density, the petal base adjacent to reproductive organs emitted significantly higher levels of volatiles than the distal petal rim. Volatile emission could also be differentiated between the two epidermal surfaces: emission from the adaxial side was significantly higher than that from the abaxial side. Similar emission patterns were also observed in other petunias, Dianthus caryophyllus (carnation) and Argyranthemum frutescens (Marguerite daisy). Analyses of transcripts involved in volatile production/emission revealed lower levels of the plasma-membrane transporter ABCG1 in the abaxial versus adaxial epidermis. Transient overexpression of ABCG1 enhanced emission from the abaxial epidermis to the level of the adaxial epidermis, suggesting its involvement in spatial emission patterns in the epidermal layers. Proboscis extension response experiments showed that differences in emission levels along the adaxial epidermis, that is, petal base versus rim, detected by GC-MS are also discernible by honeybees.

<strong><em>Gastrodia qingyunshanensis</em> (Orchidaceae: Epidendroideae)—a new holomycotrophic orchid from Guangdong, China</strong>

A new species of Gastrodia (Orchidaceae: Epidendroideae, Gastrodieae), G. qingyunshanensis, is described and illustrated from Guangdong, China. It is closely related to G. appendiculata C. S. Leou & N. J. Chung but can be distinguished by an urceolate (vs bell-like) and dark brown (vs pale greenish brown) perianth tube, the smaller petals (2.5 × 1.6 mm vs 4–5 × 5–6 mm), the shape of lip (oblong, 3×1.6mm vs ovate, 6–7×5mm), lack of elevated calli at the base of petal (vs having calli), and an appendage shorter than column (vs equal to column). The new species is only reported to occur on Qingyunshan Nature Reserve, Wengyuan County, China, and it is proposed to be Vulnerable (VU) according to the IUCN criteria.

Ethylene-regulated asymmetric growth of the petal base promotes flower opening in rose (Rosa hybrida).

Flowers are the core reproductive structures and key distinguishing features of angiosperms. Flower opening to expose stamens and gynoecia is important in cases where pollinators much be attracted to promote cross-pollination, which can enhance reproductive success and species preservation. The floral opening process is accompanied by the coordinated movement of various floral organs, particularly petals. However, the mechanisms underlying petal movement and flower opening are not well understood. Here, we integrated anatomical, physiological, and molecular approaches to determine the petal movement regulatory network using rose (Rosa hybrida) as a model. We found that PETAL MOVEMENT-RELATED PROTEIN1 (RhPMP1), a homeodomain transcription factor (TF) gene, is a direct target of ETHYLENE INSENSITIVE3, a TF that functions downstream of ethylene signaling. RhPMP1 expression was upregulated by ethylene and specifically activated endoreduplication of parenchyma cells on the adaxial side of the petal (ADSP) base by inducing the expression of RhAPC3b, a gene encoding the core subunit of the Anaphase-Promoting Complex. Cell expansion of the parenchyma on the ADSP base was subsequently enhanced, thus resulting in asymmetric growth of the petal base, leading to the typical epinastic movement of petals and flower opening. These findings provide insights into the pathway regulating petal movement and associated flower-opening mechanisms.�.

Diversity of petals in Berberidaceae: development, micromorphology, and structure of floral nectaries.

Petals are important floral organs that exhibit considerable morphological diversity in terms of colour, shape, and size. The varied morphologies of mature petals can be linked to developmental differences. The petals of Berberidaceae (a core group of Ranunculales) range from flat sheets to complex structures with nectaries, but studies on petal development and structural diversity in this group are lacking. Here, the petal development, structure, and micromorphology of seven Berberidaceae genera are characterized by microscopy to clarify the diversity of petals within this group. The results indicate that no common petal-stamen primordium exists, that petal development proceeds through five stages, and that the differentiation responsible for the diversity of the mature petals occurs during stage 4. Processes contributing to the morphological diversity of mature petals include edge thickening, gland formation, and spur formation. Nandina and Diphylleia lack nectaries. Gymnospermium has saccate nectaries, Caulophyllum has nectaries on the petal margin, Epimedium has spur nectaries, and Berberis and Mahonia have glands at the base of petals. Petal nectaries usually consist of a secretory epidermis, two to twenty layers of secretory parenchyma cells, and vascular tissues. Eleven distinct cell types were observed in the petal epidermis, three of which are secretory; papillose cells appear to be absent in Diphylleia, which shows relatively little micromorphological variation. The ancestors of Berberidaceae may have nectaries in thickened areas of their petals. The micromorphology and nectary structures of the petals in Ranunculales are also compared.

Trichomes at the Base of the Petal Are Regulated by the Same Transcription Factors as Cotton Seed Fibers.

Many polypetalous plants have a constriction at the base of the petal that leaves a small gap that can provide entry into the young flower bud before the reproductive organs are fully developed. In cotton (Gossypium hirsutum L.), this gap is occluded by tufts of short unicellular trichomes superficially resembling the fibers found on cotton seeds. We are just beginning to understand the developmental regulation of the seed fibers and have previously characterized several MIXTA-like MYB transcription factors (TFs) that are critical for correct seed fiber development but know little about the molecular regulation of other types of cotton trichomes. Here, using RNAi or dominant suppression transgenic cotton lines and natural fiber mutants, we investigated the development and regulation of the petal base trichomes. Petal base trichomes and seed trichomes were also examined across several different species within and outside of the Malvoideae. We found that the petal base trichomes are regulated by the same MYB TFs as cotton seed fibers and, since they are more widely distributed across different taxa than the seed fibers, could have preceded them in the evolution of these important textile fibers produced by some cotton species.