Pericarp Development Research Articles

Two pathways to fleshiness: fruit ontogeny in Bromelioideae species (Bromeliaceae Juss.)

Capsule-type fruits are predominant in Bromeliaceae. However, the late divergent subfamily Bromelioideae generally presents fleshy fruits, which display a diverse range of morphologies even in related genera; however, there is almost no information regarding their anatomical and ontogenetic aspects. In this study we evaluate the fruit ontogeny of species from the major lineages of Bromelioideae, to better understand the possible paths in which fleshiness can be achieved in the subfamily. Flowers at pre-anthesis and anthesis, and fruits of Acanthostachys strobilacea, Billbergia pyramidalis, and Bromelia antiacantha were collected and processed with standard methods for analysis under light microscopy. Two basic ontogenetic pathways for achieving fleshiness were identified among the examined species. In the two former species, belonging to the core Bromelioideae, the pericarp development occurs solely through cell expansion and anticlinal cell division in the mesocarp. Conversely, in B. antiacantha, belonging to the tankless lineages, the pericarp development proceeds via both periclinal and anticlinal cell divisions of the outer and inner mesocarp. The analysis of fruit anatomy in the species included in this study highlights unprecedented traits of Bromelioideae fruits, such as the presence of the pericarp´s massive extra-carpellary portion in B. antiacantha, which contains many mucilage channels and fibrous tissue, and an intrusive septum in the carpellary portion, which acts as the main nutritive portion of the fruit. Additionally, in the present study, unique features of the ovary and the fruit, essential for characterizing the species were detailed, including the elongated placental tissue and the aliform projections of A. strobilacea. Our observations highlight distinct developmental processes to fleshy fruit formation in Bromelioideae. In this way, exploring the fruit ontogenetic diversity in Bromelioideae offers an exciting opportunity for future investigations. Besides, the unique fruit features identified bring out the importance of fruits as tools for genus delineation within this subfamily.

Fruit anatomy and histogenesis in Mediterranean species of Arbutus (Ericaceae: Arbutoideae): ecological and morphogenetic aspects

Abstract Details of fruit anatomy and pericarp histogenesis were studied in Mediterranean species of Arbutus with the aim to determine the morphogenetic fruit type, to reveal the functional and ecological significance of fruit structure, and to suggest the most probable scenarios of fruit structural transformations in Arbutoideae (Ericaceae). The pericarp of the coenocarpous berries of Arbutus is differentiated into: one-layered exocarp, multilayered parenchymatous mesocarp with scattered solitary and groups of sclereids, and one-layered endocarp composed of thin-walled cells. The warts covering the fruit surface are formed by parenchymatous cells of the mesocarp and the exocarp. The process of pericarp development in Arbutus is divided into four periods, which correlate with the phenology and climatic factors of the Mediterranean region. The origin of the dormancy period in the middle part of fruit development in Arbutus is interpreted as an important adaptation to the arid Mediterranean climate. The data obtained suggest that both the berry of Arbutus and the pyrenariums of Arctostaphylos and Arctous are highly specialized fruit types that could not have derived from each other. The capsule of Hamamelis type of Enkianthoideae is recognized as the original fruit type of the berries and pyrenariums of Arbutoideae.

A Genome-Wide Analysis of the BAM Gene Family and Identification of the Cold-Responsive Genes in Pomegranate (Punica granatum L.).

Beta-amylases (BAMs, EC 3.2.1.2), belonging to a multigene family, play a pivotal role in starch breakdown and are also involved in hormonal and stress responses, notably to cold stress. Pomegranate trees (Punica granatum L.) are adapted to warm climates and are sensitive to cold temperatures. In this study, we analyzed eight PgBAM genes from the pomegranate genome dataset. These members unevenly distributed across chromosomes and were categorized into four groups based on their orthologous members. The motif composition was highly consistent among most members. In contrast, exon numbers and arrangements were conserved within groups or subgroups, whereas significant diversity was observed between different groups. A syntenic analysis revealed that three PgBAM members (PgBAM1/4/5) showed a total of 11 syntenic relationships with the BAM members from Arabidopsis, kiwifruit, and Chinese white pear, respectively. Promoter binding motif prediction suggested potential roles for PgBAMs' genes in light, stress, hormones, and development signaling. Gene expression indicated that PgBAM4 was predominantly expressed in leaves, PgBAM7 in flowers, and PgBAM8 in roots and leaves and during fruit ripening, particularly in pericarp development. A transcriptome analysis identified the starch and sucrose metabolism pathway (map00500) as a key factor in the cold stress response of cold-sensitive cultivar 'Tunisia' seedlings. PgBAM4 exhibited remarkable expression and was closely associated with the cold-responsive BAM genes, characterized by a closer phylogenetic relationship, conserved catalytic residues, and similar secondary and tertiary structures. Moreover, the differences in soluble sugar levels and PgBAM4 expression were closely associated with the varying cold stress resistance observed between 'Tunisia' and 'Sanbai' seedlings. Furthermore, yeast one-hybrid assays confirmed that PgCBF7, a critical transcription factor for enhancing freezing tolerance, binds to the promoter region of PgBAM4. Our findings provide a systematic overview of the PgBAM gene family and shed new light on the regulatory mechanisms underlying cold stress tolerance in pomegranate.

Changes in Hormonal Profiles and Corresponding Gene Expressions During the Initiation and Development of Juice Sac Primordia in Citrus Ovaries and Fruitlets

The edible part of citrus fruit is composed of juice vesicles/sacs which develop from the endocarp, the two to three inner cell layers of the white spongy peel termed albedo. Juice sac primordia usually appear 1 week after anthesis. Hormones, especially auxin and gibberellin, play a role in pericarp development during the ovary-to-fruit transition, but their effect on juice vesicle induction has not been studied. Here, hormone profiling in the pericarp and changes in the expression of their corresponding genes in the endocarp and pericarp were compared between two citrus cultivars: Calabria citron, in which juice sacs develop normally, and Yemenite citron, in which juice sac formation does not initiate. Most of the identified hormones, abscisic acid, gibberellin A4, indole-3-acetic acid, isopentenyladenine, jasmonic acid and zeatin riboside, were at higher levels in Yemenite than in Calabria. Overall, changes in abscisic acid levels in the pericarp were very well correlated with changes in the expression of abscisic acid-related genes in the endocarp. However, the application of various hormones, including abscisic acid, to Calabria flowers failed to arrest juice sac initiation. The possible involvement of abscisic acid and other hormones in the process of juice vesicle initiation and pericarp growth is discussed.

Identification of Gluconacetobacter xylinus LYP25 and application to bacterial cellulose production in biomass hydrolysate with acetic acid

Bacterial cellulose (BC) is a remarkable biomacromolecule with potential applications in food, biomedical, and other industries. However, the low economic feasibility of BC production processes hinders its industrialization. In our previous work, we obtained candidate strains with improved BC production through random mutations in Gluconacetobacter. In this study, the molecular identification of LYP25 strain with significantly improved productivity, the development of chestnut pericarp (CP) hydrolysate medium, and its application in BC fermentation were performed for cost-effective BC production process. As a result, the mutant strain was identified as Gluconacetobacter xylinus. The CP hydrolysate (CPH) medium contained 30 g/L glucose with 0.4 g/L acetic acid, whereas other candidates known to inhibit fermentation were not detected. Although acetic acid is generally known as a fermentation inhibitor, it improves the BC production by G. xylinus when present within about 5 g/L in the medium. Fermentation of G. xylinus LYP25 in CPH medium resulted in 17.3 g/L BC, a 33 % improvement in production compared to the control medium, and BC from the experimental and control groups had similar physicochemical properties. Finally, the overall process of BC production from biomass was evaluated and our proposed platform showed the highest yield (17.9 g BC/100 g biomass).

Integrated hormone and transcriptome profiles provide insight into the pericarp differential development mechanism between Mandarin 'Shatangju' and 'Chunhongtangju'.

Citrus reticulata cv. 'Chunhongtangju' was mutated from Mandarin 'Shatangju', which has been identified as a new citrus variety. Mandarin 'Chunhongtangju' fruits were late-ripening for about two months than Mandarin 'Shatangju'. To understand the pericarp differential development mechanism in Mandarin 'Shatangju' (CK) and 'Chunhongtangju' (LM), hormones and transcriptome profiles of pericarps were performed in different development stages: Young fruit stage (CK1/LM1), Expansion and Turning color stage (CK2), Expansion stage (LM2), Turning color stage (LM3), and Maturity stage (CK3/LM4). In this study, the development of LM was significantly slower, and the maturity was significantly delayed. At the same stage, most hormones in Mandarin 'Chunhongtangju' pericarps were higher than that in 'Shatangju' such as gibberellin A24, cis(+)-12-oxophytodienoic acid, and L-phenylalanine. The deficiency of hormones in late-maturing pericarps was mainly manifested in ABA, 12-OHJA, MeSAG, and ABA-GE. Differences in transcriptome profiles between the two citrus varieties are primarily observed in energy metabolism, signal transduction such as MAPK signaling pathway and plant hormone signaling, and biosynthesis of secondary metabolites. After analyzing the hormones and transcriptome data, we found that the top genes and hormones, such as Cs_ont_5g020040 (transcription elongation factor, TFIIS), Cs_ont_7g021670 (BAG family molecular chaperone regulator 5, BAG5), Cs_ont_2g025760 (40S ribosomal protein S27, Rps27), 5-deoxystrigol, salicylic acid 2-O-β-glucosid, and gibberellin A24, contributed significantly to gene transcription and hormone synthesis. This study suggests that the variances of pericarp development between the two varieties are linked to variations in the transcription levels of genes associated with energy and secondary metabolism, signal transduction related genes. These findings expand our understanding of the complex transcriptional and hormonal regulatory hierarchy during pericarp development.

Pericarp structure of Orania palindan (Blanco) Merr. in connection with the problem of determining the fruit morphogenetic type

The genus Orania Zipp. forms the monotypic clade Oranieae of the subfamily Arecoideae and includes 30 species. Representatives of the genus are pleonant single-stemmed palms of small and large size with pinnate leaves without crownshaft. With the aim to determine the morphogenetic types of fruits of the genus Orania, the features of the development and structure of the mature pericarp, we studied the fruits of Orania palindan (Blanco) Merr. at 2 development stages. The pericarp of the studied species is divided into 3 histogenetic zones: single-layer exocarp and endocarp, and multilayer mesocarp. In the mA1 zone of the mesocarp, a sclereid belt was found that performs a structural function, and in the mA2 zone, a belt of mechanical elements that performs the function of protecting the seed, due to the endocarp is not lignified and is not able to provide effective protection of the seed. According to the totality of characters, the fruits of O. palindan are most similar to the fruits of Socratea hecatonandra (Dugand) R. Bernal from the tribe Iriarteeae. Conducted research showed that the fruits of the studied species histogenetically belong to berry of Nuphar-type, and functionally to pyrenarium of Latania-type.

Structural and morphogenetic features of Erythronium L. (Liliaceae) fruits

The Lilioideae fruits are loculicidal capsules, with a large number of seeds, which are in most cases anemochorous. Gagea and Erythronium are characterized by a greater degree of endosperm development compared to the rest of the Lilioideae and indicating myrmecochoria elaiosomes on the seeds. To identify the structural features of the fruits of myrmecochore Lilioideae and to determine the morphogenetic patterns of the their fruits development, anatomical structure of the ovary wall and the pericarp of Erythronium species were studied with light microscopy method. A large number of cavities in the pericarp of the Erythronium species have been identified. The morphogenetic pattern of the presence of these cavities is the saving of resources for the development of pericarp due to the formation of elaiosomes in seeds, which is more energy- and resource-intensive compared to the production of anemochorous seeds.

Dynamic transcriptome landscape of maize pericarp development.

As a maternal tissue, the pericarp supports and protects for other components of seed, such as embryo and endosperm. Despite the importance of maize pericarp in seed, the genome-wide transcriptome pattern throughout maize pericarp development has not been well characterized. Here, we developed RNA-seq transcriptome atlas of B73 maize pericarp development based on 21 samples from 5 days before fertilization (DBP5) to 32 days after fertilization (DAP32). A total of 25 346 genes were detected in programming pericarp development, including 1887 transcription factors (TFs). Together with pericarp morphological changes, the global clustering of gene expression revealed four developmental stages: undeveloped, thickening, expansion and strengthening. Coexpression analysis provided further insights on key regulators in functional transition of four developmental stages. Combined with non-seed, embryo, endosperm, and nucellus transcriptome data, we identified 598 pericarp-specific genes, including 75 TFs, which could elucidate key mechanisms and regulatory networks of pericarp development. Cell wall related genes were identified that reflected their crucial role in the maize pericarp structure building. In addition, key maternal proteases or TFs related with programmed cell death (PCD) were proposed, suggesting PCD in the maize pericarp was mediated by vacuolar processing enzymes (VPE), and jasmonic acid (JA) and ethylene-related pathways. The dynamic transcriptome atlas provides a valuable resource for unraveling the genetic control of maize pericarp development.

ABC transporter SlABCG23 regulates chilling resistance of tomato fruit by affecting JA signaling pathway

To explore the effect and mechanism of an ATP-binding cassette transporter, SlABCG23, on the chilling resistance of tomato fruit during storage, we generated mutant using CRISPR/Cas9 technology for further investigation. This research showed under cold stress, the slabcg23 mutant fruit exhibited severe chilling injury (CI), lower jasmonic acid (JA) contents, and higher expression levels of JA signaling inhibitor, SlJAZ6, than wild-type (WT). The mutation of SlABCG23 caused a decrease in the thickness of the fruit pericarp. The expression levels of SlCBF1 and SlICE1 in slabcg23 mutant fruit were lower than those in WT fruit under cold stress. Moreover, the slabcg23 mutant fruit exhibited reduced activities of antioxidant enzymes, including superoxide dismutase, catalase and peroxidase, and increased reactive oxygen species and malondialdehyde contents. These findings indicated that SlABCG23 affects fruit resistance to CI by influencing the JA signaling pathway, fruit pericarp development, cold response signal and antioxidant capacity.

The pericarp structure and histogenesis in Enkianthus: on the ancestral fruit type in Ericaceae family

Abstract According to modern phylogenetic data, the monotypic subfamily Enkianthoideae is sister to all other subfamilies of the family Ericaceae s.l. Aiming to determine the peculiarities of development and structure of Enkianthus pericarp and to reveal the principal characters of its structure, which can be original for the Ericaceae, we have studied fruit anatomical structure at different stages of development in four species of the genus Enkianthus belonging to three sections: Meisteria, Enkiantella, Enkianthus. The pericarp of superior loculicidal capsule of Enkianthus is differentiated into three histogenetic zones: (i) one-layered exocarp, (ii) multilayered mesocarp differentiated into two histological zones: the peripheral parenchymatous one, and the inner sclerenchymatous one, and (iii) one-layered endocarp composed of tangentially elongated sclereids. It has been shown that the lignification of cells of the endocarp proceeds after the lignification of the inner zone of the mesocarp. Our investigation demonstrates that the superior loculicidal capsules of Enkianthus are capsules of Hamamelis type, which are recognized as the probable ancestral (plesiomorphic) fruit type for other subfamilies of Ericaceae. This fruit type is recognized as the original in several modes of morphogenetic transformations of fruit in Ericaceae family, from which other types of capsules, pyrenariums, and berries originated.

Integrative analysis of microRNAs and mRNAs reveals the regulatory networks of triterpenoid saponin metabolism in Soapberry (Sapindus mukorossi Gaertn.).

Triterpenoid saponin are important secondary metabolites and bioactive constituents of soapberry (Sapindus mukorossi Gaertn.) and are widely used in medicine and toiletry products. However, little is known about the roles of miRNAs in the regulation of triterpenoid saponin biosynthesis in soapberry. In this study, a total of 3036 miRNAs were identified, of which 1372 miRNAs were differentially expressed at different stages of pericarp development. Important KEGG pathways, such as terpenoid backbone biosynthesis, sesquiterpenoid and triterpenoid biosynthesis, and basal transcription factors were highlighted, as well the roles of some key miRNAs, such as ath-miR5021, han-miR3630-3p, and ppe-miR858, which may play important roles in regulating triterpenoid saponin biosynthesis. In addition, 58 miRNAs might participate in saponin biosynthesis pathways by predicting the targets of those miRNAs to 53 saponin biosynthesis structural genes. And 75 miRNAs were identified to potentially play vital role in saponin accumulation by targeting transcript factor genes, bHLH, bZIP, ERF, MYB, and WRKY, respectively, which are candidate regulatory genes in the pathway of saponin biosynthesis. The results of weighted gene coexpression network analysis (WGCNA) suggested that two saponin-specific miRNA modules and 10 hub miRNAs may participate in saponin biosynthesis. Furthermore, multiple miRNA-mRNA regulatory networks potentially involved in saponin biosynthesis were generated, e.g., ath-miR5021-SmIDI2/SmGPS5/SmbAS1/SmCYP71D-3/SmUGT74G-2, han-miR3630-3p-SmCYP71A-14/SmbHLH54/SmMYB135/SmWRKY32, and ppe-miR858-SmMYB5/SmMYB32. qRT-PCR analysis validated the expression patterns of nine miRNAs and 12 corresponding target genes. This study represents the first comprehensive analysis of miRNAs in soapberry and lays the foundation for further understanding of miRNA-based regulation in triterpenoid saponin biosynthesis.

Phylogenomic analysis of cytochrome P450 multigene family and its differential expression analysis in pepper (Capsicum annuum L.).

Plant cytochrome P450 is a multifamily enzyme widely involved in biochemical reactions for the synthesis of antioxidants, pigments, structural polymers, and defense-related compounds. Pepper (Capsicum annuum L.) is an economically important plant. A comprehensive identification and characterization of P450 genes would provide valuable information on the evolutionary relationships of genes and their functional characteristics. In this study, we identified P450 genes in pepper with the aid of bioinformatics methods to investigate the phylogenetic relation, gene structure, chromosomal localization, duplicated events, and collinearity among Solanaceae species. We identified and classified 478 genes of P450 from the pepper genome into two major clades and nine subfamilies through phylogenetic analysis. Massive duplication events were found in the P450 gene family, which may explain the expansion of the P450 gene family. In addition, we also found that these duplication genes may have undergone strict purification selection during evolution. Gene expression analysis showed that some P450 genes that belong to clan 71 in pepper may play an important role in placenta and pericarp development. Through quantitative real-time polymerase chain reaction and transcriptome analysis, we also found that many P450 genes were related to defensive and phytohormone response in pepper. These findings provide insight for further studies to identify the biological functions of the P450 genes in pepper.

Analysis of the dynamic changes of endogenous hormones for the pericarp and seed kernel of young fruit in Camellia chekiangoleosa Hu

Camellia chekiangoleosa Hu. is a unique woody oil tree with significant economic and ornamental value in China, but the fruit is easily sunburned in low-altitude areas. However, few studies on their sunburn mechanism, especially the types and content of endogenous hormones with stress resistance, have not been reported, making it challenging to take reasonable preventive measures. Here, we analyzed the endogenous hormones before sunburn and found that salicylic acid (SA) and gibberellins (GAs) were very significantly correlated between pericarp and seed kernel. However, there weren't closely related to abscisic acid (ABA), auxin, jasmonic acids (JAs), and cytokinin. The content of indole-3-carboxylic acid (ICA) and 3-indolebutyric acid (IBA) in the pericarp was higher than in seed kernel, and IBA was only found in the pericarp. GAs in seed kernel were higher than that in pericarp, and GA3 and GA15 may regulate pericarp development. Contents of trans-Zeatin (tZ), indole-3-acetic acid (IAA), and GAs in seed kernel and pericarp gradually decreased to very low, while ABA and indole-3-carboxaldehyde (ICAld) gradually increased. SA was positively correlated with ABA in pericarp and GAs and SA in seed kernel and pericarp. JAs in fruit generally showed a downward trend, and methyl jasmonate (ME-JA) appeared in pericarp.

Solanum lycopersicum CLASS-II KNOX genes regulate fruit anatomy via gibberellin-dependent and independent pathways.

The pericarp is the predominant tissue determining the structural characteristics of most fruits. However, the molecular and genetic mechanisms controlling pericarp development remain only partially understood. Previous studies have identified that CLASS-II KNOX genes regulate fruit size, shape, and maturation in Arabidopsis thaliana and Solanum lycopersicum. Here we characterized the roles of the S. lycopersicum CLASS-II KNOX (TKN-II) genes in pericarp development via a detailed histological, anatomical, and karyotypical analysis of TKN-II gene clade mRNA-knockdown (35S:amiR-TKN-II) fruits. We identify that 35S:amiR-TKN-II pericarps contain more cells around their equatorial perimeter and fewer cell layers than the control. In addition, the cell sizes but not the ploidy levels of these pericarps were dramatically reduced. Further, we demonstrate that fruit shape and pericarp layer number phenotypes of the 35S:amiR-TKN-II fruits can be overridden by the procera mutant, known to induce a constitutive response to the plant hormone gibberellin. However, neither the procera mutation nor exogenous gibberellin application can fully rescue the reduced pericarp width and cell size phenotype of 35S:amiR-TKN-II pericarps. Our findings establish that TKN-II genes regulate tomato fruit anatomy, acting via gibberellin to control fruit shape but utilizing a gibberellin-independent pathway to control the size of pericarp cells.

Integrative analysis of transcriptome and miRNAome reveals molecular mechanisms regulating pericarp thickness in sweet corn during kernel development.

Pericarp thickness affects the edible quality of sweet corn (Zea mays L. saccharata Sturt.). Therefore, breeding varieties with a thin pericarp is important for the quality breeding of sweet corn. However, the molecular mechanisms underlying the pericarp development remain largely unclear. We performed an integrative analysis of mRNA and miRNA sequencing to elucidate the genetic mechanism regulating pericarp thickness during kernel development (at 15 days, 19 days, and 23 days after pollination) of two sweet corn inbred lines with different pericarp thicknesses (M03, with a thinner pericarp and M08, with a thicker pericarp). A total of 2,443 and 1,409 differentially expressed genes (DEGs) were identified in M03 and M08, respectively. Our results indicate that phytohormone-mediated programmed cell death (PCD) may play a critical role in determining pericarp thickness in sweet corn. Auxin (AUX), gibberellin (GA), and brassinosteroid (BR) signal transduction may indirectly mediate PCD to regulate pericarp thickness in M03 (the thin pericarp variety). In contrast, abscisic acid (ABA), cytokinin (CK), and ethylene (ETH) signaling may be the key regulators of pericarp PCD in M08 (the thick pericarp variety). Furthermore, 110 differentially expressed microRNAs (DEMIs) and 478 differentially expressed target genes were identified. miRNA164-, miRNA167-, and miRNA156-mediated miRNA–mRNA pairs may participate in regulating pericarp thickness. The expression results of DEGs were validated by quantitative real-time PCR. These findings provide insights into the molecular mechanisms regulating pericarp thickness and propose the objective of breeding sweet corn varieties with a thin pericarp.

BEHAVIOR AND WATER USE EFFICIENCY OF EIGHT TUNISIAN VARIETIES OF CHICKPEA (CICER ARIETINUM L.) IN TWO BIOCLIMATIC STAGES

This work was carried out from December 2016 to June 2017 in two different regions on the north of Tunisia belong to the Sub-humid bioclimatic stage on Beja and the Semi-arid bioclimatic stage on Oued Mliz. It aims to identify the varieties of chickpea adaptable on each bioclimatic stage and to evaluate the efficiency of water use for some varieties of chickpea. Indeed, analysis of yield parameters such as biological yields, weight of hundred seeds, seeds yield, number of seeds. All varieties were grown in rainfed conditions. For the sub-humid and semi-arid bioclimatic sites plant have received respectively an amount of water of 346 and 261mm. The results show that there is a significant correlation between these parameters. The cultivation of the collection of eight varieties of chickpea in rainfed soil showed an important adaptation to drought. The number of pods marked in Beja1 and Nayer varieties are the highest, because of the ability to fill the pods during the year. While other varieties have a lower number of pods indicating that spring drought could be the cause of high flower abortion, pericarp development and empty pod formation. This research revealed that in the sub-humid bioclimatic stage, all varieties adapt and produce better than on the semi-arid. The semi-arid Tunisian is characterized by the final drought which causes the hydrous stress at chickpea. The conduit of this last in these zones is dependent on the selection of the varieties early and resistant to the water deficit.

Phytohormone and transcriptome of pericarp reveals jasmonate and LcMYC2 are involved in neral and geranial biosynthesis in Litsea cubeba

Litsea cubeba (Lour.) Person (Lauraceae) is a famous essential oil tree that produces L. cubeba essential oil (LCEO) in the pericarp. LCEO, mainly containing neral and geranial (~80%), has been widely used in medical treatment, cosmetics, food and other fields. Knowledge of the development of the L. cubeba pericarp would provide an important basis for LCEO production and genetic breeding. Here, according to the characteristics of the pericarp development process, we provide the phytohormone profiles, including auxin, gibberellin (GA), abscisic acid (ABA), cytokinin (CK), and jasmonate (JA), at 8 timepoints covering the development process of fruit growth, maturation and fruit ripening periods. The results indicated that only the dynamics of JA were consistent with the increasing trend of LCEO, neral, and geranial. Meanwhile, RNA-seq was used to investigate the expression of the genes, especially the genes involved in signal transduction pathways of phytohormones, during L. cubeba pericarp development. The crosstalk among these phytohormone-responsive genes indicated that the hub transcription factor LcMYC2 was also involved in the JA signalling pathway. Furthermore, treatment with MeJA and transient overexpression of LcMYC2 both resulted in significant accumulation of neral and geranial in L. cubeba. Finally, LcMYC2 was verified to promote neral and geranial biosynthesis by transient expression assay, and LcMYC2 enhanced the transcription of LcTPS42 and LcGPPS.SSU1 promoters are key enzymes responsible for the biosynthesis of the above component by yeast one-hybrid (Y1H) and dual-luciferase (dual-LUC) assays. Our data not only provided the profiles of phytohormones and the transcriptome during the development process of the pericarp but also identified the important roles of JA and the hub regulator LcMYC2 in the accumulation of LCEO in the L. cubeba pericarp.

Gynoecium and fruit histology, structure and development in corky-warted representatives of Livistoninae (Trachycarpeae: Coryphoideae: Arecaceae)

Abstract Representatives of three genera of Livistoninae (Johannesteijsmannia, Licuala and Pholidocarpus) develop corky-warted fruits in contrast to fruit with smooth surfaces in most other representatives of the ‘apocarpous clade’ of Arecaceae subfamily Coryphoideae. The present developmental study is focused on revealing the anatomical peculiarities of the fruit structure of corky-warted species of Livistoninae and tracing the development of their pericarp. Our study shows that the fruits of Johannesteijsmannia, Licuala bintulensis and Pholidocarpus macrocarpus are drupes of the Rhapis type and that the warts on their fruit surface originate soon after gynoecium pollination as the result of two or three developmental events: (1) suberinization of the exocarp cells; (2) progressive multiplication and growth of the outer zone of the mesocarp; and (3) cracking of the peripheral zone of the pericarp. The warts of taxa of Livistoninae develop at the mid stages of fruit organogenesis and are referred to as either alive, composed of parenchymatous cells and sclereids (species of Licuala and Pholidocarpus), or dead, consisting of cells with suberized walls and sclereids (Johannesteijsmannia). The nests of sclereids comprising the stone of Johannesteijsmannia spp. remain disunited during pericarp development until late developmental stages when the formation of a continuous sclerenchymatous layer occurs, which differs from other representatives of the ‘apocarpous clade’ of Coryphoideae with a continuous layer of sclereids persisting during fruit development (as in L. bintulensis). It is shown that the development of the stone within the drupes of the Rhapis type can be different even in closely related taxa. The recognition of the fruits of studied taxa of Livistoninae as drupes of the Rhapis type like the fruit of many other taxa of Trachycarpeae and the ‘apocarpous clade’ of Coryphoideae suggest this character as a synapomorphy for this tribe and the whole clade.

A comparative approach to understanding the ovule, seed, and fruit development in Bulbostylis (Cyperaceae: Cyperoideae: Abildgaardieae).

In the present work, we study the ovule, seed, and fruit development in six Bulbostylis species in order to characterize the genus in a comparative approach and to identify the characteristics that can be used in taxonomy and phylogeny. Flowers and fruits at different developmental stages were analyzed using LM and SEM after processing according to standard techniques. The species studied have the following: anatropous and bitegmic ovules, weak crassinucellar ovules, obturator of integumentary origin, monosporic embryo sac of the Polygonum type, nuclear endosperm, hypostase formation, seed coat formed by tanniferous endotegmen and exotesta, and Bulbostylis-type embryo. On the other hand, the pericarp development constitutes the main variation within Bulbostylis since the cells of the exocarp may or may not present starch grains, and their inner periclinal walls may be slightly or deeply concave depending on the degree of development of the mesocarp sclereids. In a taxonomic context, the results herein obtained are in conflict with studies which suggest infrageneric groupings based on fruit micromorphology, and also with the relationship among the Bulbostylis species based on molecular analysis. This work contributes to a better understanding of the reproductive anatomy and embryology in Bulbostylis, and reveals the first insights about the origin of multiple embryos in Cyperaceae. Given the frequent presence of polyembryony in Bulbostylis, and the poor mention of this condition in the family, this work highlights an aspect in the anatomy of Cyperaceae that must be re-explored.