Tube Growth Research Articles

Synthesis, characterization, visualization, and growth mechanism of macro-sized tubular MgO crystals formed in situ from refractory magnesia with aluminum

MgO crystals are widely used in many industries for resisting thermal and corrosion resistance. Macro-sized tubular MgO crystals with porous structures were successfully synthesized via the compaction of magnesia and aluminum powder at temperatures above 1400 °C in an air atmosphere. The morphology and densification of the MgO tube could be easily controlled by the shape of the bore on the Al2O3 lid and the heat treatment temperature. The bore of the Al2O3 crucible was critical for MgO tube growth. The thermite reaction produced a large amount of Mg vapor, and the oxygen in the crucible was squeezed out through the bore. Owing to the constraint of the air atmosphere, the MgO vapor flowing out of the crucible, which is generated by the oxidation of the Mg vapor, is preferentially deposited around the bore to form a MgO wall. Macro-sized tubular MgO crystals were obtained by MgO wall growth. A high-temperature visualization system based on monochromatic light was applied to observe the MgO tube growth process, and the growth mechanism was confirmed. These findings can be expected to enhance the aluminum-containing magnesia-based refractories with self-healing and presents a promising strategy for the economical production of high-purity MgO.

Cellulose accumulation mediated by PbrCSLD5, a cellulose synthase-like protein, results in cessation of pollen tube growth in Pyrus bretschneideri.

Cellulose, a key component of the cell wall, plays an important role in maintaining the growth of pollen tubes. However, the molecular mechanism of cellulose participating in the cessation of pear pollen tube growth remains unclear. Here, we reported that at 15 h post-cultured (HPC), the slow-growth pear pollen tubes showed thickened cell walls and cellulose accumulation in the inner wall. Transcriptome data and quantitative real-time PCR analysis showed that PbrCSLD5, a cellulose synthesis-like gene, was highly expressed in the 15 HPC pear pollen tubes. Knockdown of PbrCSLD5 caused a decrease in cellulose content in pear pollen tubes. Moreover, PbrCSLD5 overexpression in Arabidopsis resulted in the accumulation of cellulose and disruption of normal pollen tube growth. Transcription factor PbrMADS52 was found to bind to the promoter of PbrCSLD5 and enhanced its expression. Our results suggested that the PbrMADS52-PbrCSLD5 signaling pathway led to increased cellulose content in the pear pollen tube cell wall, thereby inhibiting pollen tube growth. These results provided new insights into the regulation of pollen tube growth.

Proteomic Analysis of Pollen–Stigma Interaction between Vitis rotundifolia and Vitis vinifera

Muscadine grape (Vitis rotundifolia) is highly resistant to many diseases and insects that attack european grape (Vitis vinifera). However, distant hybridization incompatibility between V. rotundifolia (female) and V. vinifera (male) impedes the utilization of V. rotundifolia in grape breeding. This study used fourth-dimension label-free protein quantitation to detect the key genes and pathways in the V. rotundifolia stigma after self-pollination (V. rotundifolia × V. rotundifolia) and cross-pollination (V. rotundifolia × V. vinifera). A histological analysis showed that pollen tube growth in the stigma of V. rotundifolia was arrested 8 hours after cross-pollination, but not after self-pollination. A proteomic analysis identified 32 differentially expressed proteins (DEPs) in the stigma of V. rotundifolia between self-pollination and cross-pollination. A heatmap analysis grouped these DEPs into four clusters. The top gene ontology terms were ATPase-coupled transmembrane transporter activity, extracellular region, DNA replication, and cellular carbohydrate biosynthetic process. A Kyoto Encyclopedia of Genes and Genomes analysis revealed that these DEPs participated in DNA replication and starch and sucrose metabolism pathways. The downregulated A5AY88, D7TJ35, D7SU26, F6HJI1, and F6GUE7 may have a role in cross incompatibility. This study revealed the cross incompatibility of grapes at histological and proteomic levels.

RNAi-Mediated Knockdown of Calreticulin3a Impairs Pollen Tube Growth in Petunia.

Pollen tube growth depends on several complex processes, including exo/endocytosis, cell wall biogenesis, intracellular transport, and cell signaling. Our previous results provided evidence that calreticulin (CRT)—a prominent calcium (Ca2+)-buffering molecular chaperone in the endoplasmic reticulum (ER) lumen—is involved in pollen tube formation and function. We previously cloned and characterized the CRT gene belonging to the CRT1/2 subgroup from Petunia hybrida (PhCRT1/2), and found that post-transcriptional silencing of PhCRT1/2 expression strongly impaired pollen tube growth in vitro. Here, we report cloning of a new PhCRT3a homolog; we identified the full-length cDNA sequence and described its molecular characteristics and phylogenetic relationships to other plant CRT3 genes. Using an RNA interference (RNAi) strategy, we found that knockdown of PhCRT3a gene expression caused numerous defects in the morphology and ultrastructure of cultivated pollen tubes, including disorganization of the actin cytoskeleton and loss of cytoplasmic zonation. Elongation of siPhCRT3a pollen tubes was disrupted, and some of them ruptured. Our present data provide the first evidence that PhCRT3a expression is required for normal pollen tube growth. Thus, we discuss relationships between diverse CRT isoforms in several interdependent processes driving the apical growth of the pollen tube, including actomyosin-dependent cytoplasmic streaming, organelle positioning, vesicle trafficking, and cell wall biogenesis.

Hormonal Signaling in the Progamic Phase of Fertilization in Plants

Pollen–pistil interaction is a basic process in the reproductive biology of flowering plants and has been the subject of intense fundamental research that has a pronounced practical value. The phytohormones ethylene (ET) and cytokinin (CK) together with other hormones such as auxin, gibberellin (GA), jasmonic acid (JA), abscisic acid (ABA), and brassinosteroids (BRs) influence different stages of plant development and growth. Here, we mainly focus on the information about the ET and CK signaling in the progamic phase of fertilization. This signaling occurs during male gametophyte development, including tapetum (TAP) cell death, and pollen tube growth, including synergid programmed cell death (PCD) and self-incompatibility (SI)-induced PCD. ET joins the coordination of successive events in the developing anther, including the TAP development and cell death, anther dehiscence, microspore development, pollen grain maturation, and dehydration. Both ET and CK take part in the regulation of pollen–pistil interaction. ET signaling accompanies adhesion, hydration, and germination of pollen grains in the stigma and growth of pollen tubes in style tissues. Thus, ET production may be implicated in the pollination signaling between organs accumulated in the stigma and transmitted to the style and ovary to ensure successful pollination. Some data suggest that ET and CK signaling are involved in S-RNase-based SI.

Metal-organic aerogel derived hierarchical porous metal-carbon nanocomposites as efficient bifunctional electrocatalysts for overall water splitting

An efficient strategy to construct non-noble metal-base electrocatalysts for water splitting is the direct carbonization of metal–organic aerogel composites. Herein for the first time, a novel tube-like metal–carbon nanocomposite with encapsulated small-size individual Fe, Cr and Ni nanoparticles, is prepared by the carbonization of a FeCr-doped Ni-benzenetricarboxylate aerogel. The slender skeleton of the aerogel, supercritical drying and Cr doping alleviates metal aggregation and facilitates the in-situ growth of carbon tubes. This nanocomposite exhibits remarkably low overpotential of the hydrogen evolution reaction (137 mV) and oxygen evolution reaction (220 mV). Further, the cell voltage could be as low as 1.54 V with the current density of 10 mA cm−2 and illustrates excellent stability under a continuous operation for 50 h. This non-noble metal-base electrocatalyst is comparable to noble metal-based electrocatalysts and the impressive performance is ascribed to the abundant active catalytic sites and short reactant diffusion pathways. This work demonstrates great capability of aerogel derivation in the highly active electrocatalyst design for promising electrochemical applications.

Hybridization and introgression are prevalent in Southern European Erysimum (Brassicaceae) species.

Hybridization is a common and important force in plant evolution. One of its outcomes is introgression - the transfer of small genomic regions from one taxon to another by hybridization and repeated backcrossing. This process is believed to be common in glacial refugia, where range expansions and contractions can lead to cycles of sympatry and isolation, creating conditions for extensive hybridization and introgression. Polyploidization is another genome-wide process with a major influence on plant evolution. Both hybridization and polyploidization can have complex effects on plant evolution. However, these effects are often difficult to understand in recently evolved species complexes. We combined flow cytometry, analyses of transcriptomic sequences and pollen tube growth assays to investigate the consequences of polyploidization, hybridization and introgression on the recent evolution of several Erysimum (Brassicaceae) species from the South of the Iberian Peninsula, a well-known glacial refugium. This species complex differentiated in the last 2 million years, and its evolution has been hypothesized to be determined mainly by polyploidization, interspecific hybridization and introgression. Our results support a scenario of widespread hybridization involving both extant and 'ghost' taxa. Several taxa studied here, most notably those with purple corollas, are polyploids, probably of allopolyploid origin. Moreover, hybridization in this group might be an ongoing phenomenon, as pre-zygotic barriers appeared weak in many cases. The evolution of Erysimum spp. has been determined by hybridization to a large extent. Species with purple (polyploids) and yellow flowers (mostly diploid) exhibit a strong signature of introgression in their genomes, indicating that hybridization occurred regardless of colour and across ploidy levels. Although the adaptive value of such genomic exchanges remains unclear, our results demonstrate the significance of hybridization for plant diversification, which should be taken into account when studying plant evolution.

The Balance between Different ROS on Tobacco Stigma during Flowering and Its Role in Pollen Germination.

The concept of ROS as an important factor controlling pollen germination and tube growth has become generally accepted in the last decade. However, the relationship between various ROS and their significance for the success of in vivo germination and fertilization remained unexplored. For the present study, we collected Nicotiana tabacum stigma exudate on different stages of stigma maturity before and after pollination. Electron paramagnetic resonance (EPR) and colorimetric analysis were used to assess levels of O•2− and H2O2 on stigma. Superoxide dismutase activity in the stigma tissues at each stage was evaluated zymographically. As the pistil matured, the level of both ROS decreased markedly, while the activity of SOD increased, and, starting from the second stage, the enzyme was represented by two isozymes: Fe SOD and Cu/Zn SOD, which was demonstrated by the in-gel inhibitory analysis. Selective suppression of Cu/Zn SOD activity shifted the ROS balance, which was confirmed by EPR. This shift markedly reduced the rate of pollen germination in vivo and the fertilization efficiency, which was estimated by the seed set. This result showed that hydrogen peroxide is a necessary component of stigma exudate, accelerates germination and ensures successful reproduction. A decrease in O•2− production due to NADPH oxidase inhibition, although it slowed down germination, did not lead to a noticeable decrease in the seed set. Thus, the role of the superoxide radical can be characterized as less important.

Vesicle trafficking in Arabidopsis pollen tubes

The delivery of sperm cells via tip-growing pollen tubes is an innovation of seed plants and shows the importance of pollen tubes for reproduction and their specific growth kinetics. Fast-growing pollen tubes demand an extensive and dynamic vesicular trafficking network to build new cell membrane and wall, to deliver proteins among endomembrane compartments, and also to respond to external stimuli for growth adjustment. In this review, we summarize current findings on endomembrane compartments and vesicular trafficking routes of pollen tubes, comparing and contrasting their features with those of most somatic cells. We discuss the importance of membrane homeostasis, either at the plasma membrane (PM) or between PM-targeted trafficking and vacuolar trafficking, for pollen tube growth. We also provide perspectives to facilitate future studies of vesicular trafficking in pollen tubes.

Involvement of three ABRE-binding factors in the gametophytic self-incompatibility reaction in pear

Self-incompatibility (SI) facilitates the rejection of pollen by self S-RNase. It is believed that a large number of genes are responsive to SI reactions; however, little is known about the transcriptional regulation of these genes. Herein, we explored the role of ABRE-binding factor (ABF) in gametophytic self-incompatibility (GSI). Phylogenetic analysis showed that eight ABF genes in pear clustered with five ABF genes in Arabidopsis. Of these ABF genes, PbABF.E.1 and PbABF.E.2 were expressed in all tissues, and PbABF.B was expressed in most tissues. These three ABF genes were also detected in the self- and cross-pollinated styles. Additionally, RNA-Seq analysis revealed 11,476 genes that were differentially expressed between the self- and cross-pollinated styles at 24, 48, and/or 72 h after pollination. Of these differentially expressed genes (DEGs), 278 were differentially expressed between the self- and cross-pollinated styles at any stage and thus are responsive to the GSI reaction. Notably, abscisic acid-responsive elements were detected in the promoter sequences of the 1213 DEGs including the six genes negatively correlated with pollen tube growth. The dual-luciferase assay showed that the promoter of these six genes was activated by PbABF.B, PbABF.E.1, and/or PbABF.E.2. Therefore, PbABF.B, PbABF.E.1, and PbABF.E.2 were involved in the GSI reaction by mediating the expression of genes responsive to the GSI reaction.

Fast and flexible processing of large FRET image stacks using the FRET-IBRA toolkit.

Ratiometric time-lapse FRET analysis requires a robust and accurate processing pipeline to eliminate bias in intensity measurements on fluorescent images before further quantitative analysis can be conducted. This level of robustness can only be achieved by supplementing automated tools with built-in flexibility for manual ad-hoc adjustments. FRET-IBRA is a modular and fully parallelized configuration file-based tool written in Python. It simplifies the FRET processing pipeline to achieve accurate, registered, and unified ratio image stacks. The flexibility of this tool to handle discontinuous image frame sequences with tailored configuration parameters further streamlines the processing of outliers and time-varying effects in the original microscopy images. FRET-IBRA offers cluster-based channel background subtraction, photobleaching correction, and ratio image construction in an all-in-one solution without the need for multiple applications, image format conversions, and/or plug-ins. The package accepts a variety of input formats and outputs TIFF image stacks along with performance measures to detect both the quality and failure of the background subtraction algorithm on a per frame basis. Furthermore, FRET-IBRA outputs images with superior signal-to-noise ratio and accuracy in comparison to existing background subtraction solutions, whilst maintaining a fast runtime. We have used the FRET-IBRA package extensively to quantify the spatial distribution of calcium ions during pollen tube growth under mechanical constraints. Benchmarks against existing tools clearly demonstrate the need for FRET-IBRA in extracting reliable insights from FRET microscopy images of dynamic physiological processes at high spatial and temporal resolution. The source code for Linux and Mac operating systems is released under the BSD license and, along with installation instructions, test images, example configuration files, and a step-by-step tutorial, is freely available at github.com/gmunglani/fret-ibra.

Plant biology: Local auxin synthesis drives pollen maturation in barley

Pollen grains stock up on starch to power germination and pollen tube growth upon pollination. New findings in barley show that localized auxin biosynthesis by a YUC flavin monooxygenase leads to reprogramming energy metabolism during pollen maturation.

Self-Incompatibility of Camellia weiningensis Y.K. Li.

This study compared the pollen tube growth, fruit setting, and seed setting characteristics of Camellia weiningensis Y.K. Li. under self- and cross-pollination to identify its self-incompatibility characteristics and types. C. weiningensis pollen tube growth was observed by fluorescence and scanning electron microscopy, and a field experiment with manual pollination verified fruit and seed setting characteristics. Both self- and cross-pollinated pollen germinated from the stigma. At 72 h after cross-pollination, the pollen tube reached the style base, with tube growth showing a slow-fast-slow pattern. The tube growth speed was maximal, 343.36 μm·h−1, at 12–24 h after pollination. For self-pollination, the pollen did not germinate on the stigma 4 h before pollination. At 12–24 h after pollination, the growth rate was maximal at 263.36 μm·h−1. At 96 h, a small amount of pollen reached the style base and stagnated. The pollen tube end showed callose reactions, such as abnormal swelling, distortion, and brightness. In the field experiment, the fruit setting rate under cross-pollination was 68.5%, while that under self-pollination was 15.3%. When the fruit grew to maturity, the growth dynamics of the transverse and longitudinal diameters showed a “slow-fast-slow”, S-shaped curve. The number of aborted selfed and outcrossed seeds was 13.9 and 4.7, respectively. Thus, C. weiningensis showed self-incompatibility. The self-incompatibility reaction occurred at the style base and represented prezygotic self-incompatibility. The self-incompatibility of C. weiningensis is one of the main reasons for its low seed setting rate, which should be fully considered in cross breeding.

Exploration of molecular mechanism of intraspecific cross-incompatibility in sweetpotato by transcriptome and metabolome analysis.

Cross-incompatibility, frequently happening in intraspecific varieties, has seriously restricted sweetpotato breeding. However, the mechanism of sweetpotato intraspecific cross-incompatibility (ICI) remains largely unexplored, especially for molecular mechanism. Treatment by inducible reagent developed by our lab provides a method to generate material for mechanism study, which could promote incompatible pollen germination and tube growth in the ICI group. Based on the differential phenotypes between treated and untreated samples, transcriptome and metabolome were employed to explore the molecular mechanism of sweetpotato ICI in this study, taking varieties ‘Guangshu 146’ and ‘Shangshu 19’, a typical incompatible combination, as materials. The results from transcriptome analysis showed oxidation–reduction, cell wall metabolism, plant–pathogen interaction, and plant hormone signal transduction were the essential pathways for sweetpotato ICI regulation. The differentially expressed genes (DEGs) enriched in these pathways were the important candidate genes to response ICI. Metabolome analysis showed that multiple differential metabolites (DMs) involved oxidation–reduction were identified. The most significant DM identified in comparison between compatible and incompatible samples was vitexin-2-O-glucoside, a flavonoid metabolite. Corresponding to it, cytochrome P450s were the most DEGs identified in oxidation–reduction, which were implicated in flavonoid biosynthesis. It further suggested oxidation–reduction play an important role in sweetpotato ICI regulation. To validate function of oxidation–reduction, reactive oxygen species (ROS) was detected in compatible and incompatible samples. The green fluorescence was observed in incompatible but not in compatible samples. It indicated ROS regulated by oxidation–reduction is important pathway to response sweetpotato ICI. The results in this study would provide valuable insights into molecular mechanisms for sweetpotato ICI.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11103-022-01259-8.

Development of an HRMA-Based Marker Assisted Selection (MAS) Approach for Cost-Effective Genotyping of S and M Loci Controlling Self-Compatibility in Apricot (Prunus armeniaca L.).

The apricot species is characterized by a gametophytic self-incompatibility (GSI) system. While GSI is one of the most efficient mechanisms to prevent self-fertilization and increase genetic variability, it represents a limiting factor for fruit production in the orchards. Compatibility among apricot cultivars was usually assessed by either field pollination experiments or by histochemical evaluation of in vitro pollen tube growth. In apricots, self-compatibility is controlled by two unlinked loci, S and M, and associated to transposable element insertion within the coding sequence of SFB and ParM-7 genes, respectively. Self-compatibility has become a primary breeding goal in apricot breeding programmes, stimulating the development of a rapid and cost-effective marker assisted selection (MAS) approach to accelerate screening of self-compatible genotypes. In this work, we demonstrated the feasibility of a novel High Resolution Melting Analysis (HRMA) approach for the massive screening of self-compatible and self-incompatible genotypes for both S and M loci. The different genotypes were unambiguously recognized by HRMA, showing clearly distinguishable melting profiles. The assay was developed and tested in a panel of accessions and breeding selections with known self-compatibility reaction, demonstrating the potential usefulness of this approach to optimize and accelerate apricot breeding programmes.

Boron Effects on Fruit Set, Yield, Quality and Paternity of Macadamia

Many tree crops experience sub-optimal yields and low fruit quality due to inadequate pollination, low fruit set, and poor crop nutrition. Boron (B) is a critical crop nutrient for fruit set because B levels affect pollen germination and pollen tube growth. However, the relationship between floral B concentration and fruit set is not well understood. The aim of this study was to determine the effect of B applications on the initial fruit set, yield, quality, and paternity of macadamia (Macadamia integrifolia). Cultivar ‘816’ trees received one of three treatments: (a) 0 g, (b) 15 g, or (c) 30 g B per tree prior to flowering. Boron application increased the B concentration of macadamia flowers. Application of 15 g B increased fruit set at 3 weeks after peak anthesis, but this higher initial fruit set was not translated into higher fruit set at 6 or 10 weeks after peak anthesis or higher yield. Boron application increased B concentrations in kernels but did not affect nut-in-shell (NIS) mass, kernel mass, kernel recovery, kernel oil concentration or incidence of whole kernels. Cultivar ‘816’ was highly outcrossing, with 97–98% cross-paternity among kernels from all treatments. Our results indicate that higher B concentration in macadamia flowers can be associated with an increased initial fruit set. However, high B levels did not affect yield, nut quality, or the proportion of self-pollinated fruit at maturity. The heavy dependence on outcrossing highlights the importance of inter-planting different cultivars and managing bee hives to sustain the productivity of macadamia orchards.

Uncovering the Secrets of Secretory Fluids During the Reproductive Process in Ginkgo biloba

Reproduction is an essential process for all organisms. Although our understanding of the reproductive mechanism in angiosperms has rapidly advanced in recent years, it still lags behind that of gymnosperms. As an ancient gymnosperm, Ginkgo biloba has a remarkable evolutionary history and occupies an important phylogenetic position, representing one of the most ancient and primitive modes of reproduction among seed plants. G. biloba is an archegoniate, where an egg cell develops inside an archegonium; it has a particular pollen chamber and archegonial chamber along with flagellated gametes (spermatozoids). Among these processes, secretions play an important role. In this study, we review the progress on understanding the mechanisms underlying the production and function of pollination drops (PDs), and fertilization fluid in G. biloba. We also highlight recent achievements that have considerably advanced our understanding of the interactions between PDs and pollen, and how PDs are endogenously and intracellularly transported. Finally, we discuss novel insights into the small RNAs of PD transport and the mechanisms of precisely guiding pollen tube growth in G. biloba. By reviewing these results, we demonstrate the structural patterns of G. biloba pollination and fertilization, thus reproducing the uniqueness of the sexual reproduction of ancient plants.

Pollen tube growth in Calotropis procera is controlled by environmental changes: does it have an impact on delayed fertilization?

Calotropis procera (Apocynaceae) is a Sudanian plant that grows throughout the eastern Saharo-Arabian region. In Israel, it grows along the Rift Valley under extremely hot and dry climatic conditions. In C. procera, as in many other Apocynaceae, the nectar is secreted in the flowers from the nectaries located inside the stigmatic chamber, with the excess flowing via the capillary system into special reservoirs (cucculi). The nectar has two functions: it is used as a reward to attract pollinating insects and it serves as the germination medium for pollen grains. Under natural conditions the nectar concentration is subjected to a large variability, ranging from 22-68% sucrose. The aim of this study was to elucidate the effects of the natural fluctuations of nectar concentration on pollen germination and pollen tube growth, and their possible role in delaying fertilization in Calotropis procera. We followed the process of pollen germination under various experimental sucrose concentrations simulating the nectar. We found that the optimal concentration of a sucrose medium for pollen germination is 20%. However, if the already-germinated pollen grains are subjected to high sucrose concentration for different periods of time (between one and three hours), elongation of the pollen tubes is inhibited. In all the experimental groups, the pollen tubes renewed their elongation following a reduction of the sucrose. In conclusion, we found that C. procera pollen grains’ germination is able to adjust to the large fluctuations in sucrose concentration, caused by the changes in temperature and relative humidity conditions of the plant’s habitat during the day. This phenomenon probably enables postponing the fertilization towards a time of better conditions and enables the plant to retain the pollen tubes alive, albeit inactive, and thus allow the plant to overcome temporary harsh conditions and develop seeds.

Breakdown of Self-Incompatibility in Citrus by Temperature Stress, Bud Pollination and Polyploidization

Self-incompatibility (SI) is present in around half of all species of flowering plants. SI limits endogamy and contributes to increased genetic diversity. SI is a very important trait in citrus because, when coupled with parthenocarpy, it allows seedless fruit production. Otherwise, SI is an impediment to genetic studies and breeding programs. Temperature stress, bud pollination and polyploidization can induce the breakdown of the SI mechanism in several species. In this work, we investigated how the SI mechanism can be broken down in two self-incompatible diploid citrus genotypes: ‘Fortune’ mandarin and ‘Clemenules’ clementine. The influence of temperature stress on the SI mechanism was assessed in self-pollinated flowers of ‘Fortune’ mandarins subjected to 2 temperature regimes (10 °C and 30 °C), whereas the bud pollination effect was investigated in the same genotype and in ‘Clemenules’ clementines cultivated under field conditions. The tetraploid ‘Clemenules’ clementine cultivated under field conditions was used to study if tetraploidization can bypass the SI reaction. Histological observations of pollen tube growth and seed production in self-pollinated flowers were used to evaluate the breakdown of SI, while the genetic analysis with SSR and SNP markers confirmed that all recovered plants were zygotic and had been originated by selfing. Our results confirm that the SI reaction can be surpassed by temperature stress, bud pollination and tetraploidy. To our knowledge, this is the first report in citrus in which the SI reaction breakdown by these three different strategies is demonstrated by molecular markers.

Investigating the Mechanism of Unilateral Cross Incompatibility in Longan (Dimocarpus longan Lour.) Cultivars (Yiduo × Shixia).

Longan (Dimocarpus longan Lour.) is an important subtropical fruit tree in China. Nearly 90% of longan fruit imports from Thailand are from the cultivar Yiduo. However, we have observed that there exists a unilateral cross incompatibility (UCI) when Yiduo is used as a female parent and Shixia (a famous Chinese cultivar) as a male parent. Here, we performed a comparative transcriptome analysis coupled with microscopy of pistils from two reciprocal pollination combinations [Shixia♂ × Yiduo♀(SY) and Yiduo♀ × Shixia♂(YS)] 4, 8, 12, and 24 h after pollination. We also explored endogenous jasmonic acid (JA) and jasmonyl isoleucine (JA-Ile) levels in pistils of the crosses. The microscopic observations showed that the UCI was sporophytic. The endogenous JA and JA-Ile levels were higher in YS than in SY at the studied time points. We found 7,251 differentially expressed genes from the transcriptome analysis. Our results highlighted that genes associated with JA biosynthesis and signaling, pollen tube growth, cell wall modification, starch and sucrose biosynthesis, and protein processing in endoplasmic reticulum pathways were differentially regulated between SY and YS. We discussed transcriptomic changes in the above-mentioned pathways regarding the observed microscopic and/or endogenous hormone levels. This is the first report on the elaboration of transcriptomic changes in longan reciprocal pollination combination showing UCI. The results presented here will enable the longan breeding community to better understand the mechanisms of UCI.