Pear Pollen Research Articles

PbrRALF2-elicited reactive oxygen species signaling is mediated by the PbrCrRLK1L13-PbrMPK18 module in pear pollen tubes

Rapid alkalinization factors (RALFs) are cysteine-rich peptides that play important roles in a variety of biological processes, such as cell elongation and immune signaling. Recent studies in Arabidopsis have shown that RALFs regulate pollen tube growth via plasma membrane receptor-like kinases (RLKs). However, the downstream signal transduction mechanisms of RLKs in pollen tubes are unknown. Here, we identified PbrRALF2, a pear (Pyrus bretschneideri) pollen RALF peptide that inhibits pollen tube growth. We found that PbrRALF2 interacts with a malectin-like domain-containing RLK, PbrCrRLK1L13. The relative affinity between PbrRALF2 and PbrCrRLK1L13 was at the submicromolar level, which is consistent with the values of ligand–receptor kinase pairs and the physiological concentration for PbrRALF2-mediated inhibition of pollen tube growth. After binding to its extracellular domain, PbrRALF2 activated the phosphorylation of PbrCrRLK1L13 in a dose-dependent manner. We further showed that the MAP kinase PbrMPK18 is a downstream target of PbrCrRLK1L13 that mediates PbrRALF2-elicited reactive oxygen species (ROS) production. The excessive accumulation of ROS inhibits pollen tube growth. We show that MPK acts as a mediator for CrRLK1L to stimulate ROS production, which might represent a general mechanism by which RALF and CrRLK1L function in signaling pathways.

Characterization of the pectin methylesterase inhibitor gene family in Rosaceae and role of PbrPMEI23/39/41 in methylesterified pectin distribution in pear pollen tube.

Pectin methylesterase inhibitor gene family in the seven Rosaceae species (including three pear cultivars) is characterized and three pectin methylesterase inhibitor genes are identified to regulate pollen tube growth in pear. Pectin methylesterase inhibitor (PMEI) participates in a variety of biological processes in plants. However, the information and function of PMEI genes in Rosaceae are largely unknown. In this study, a total of 423 PMEI genes are identified in the genomes of seven Rosaceae species. The PMEI genes in pear are categorized into five subfamilies based on structural analysis and evolutionary analysis. WGD and TD are the main duplication events in the PMEI gene family of pear. Quantitative real-time PCR analysis indicates that PbrPMEI23, PbrPMEI39, and PbrPMEI41 are increasingly expressed during pear pollen tube growth. Under the treatment of recombinant proteins PbrPMEI23, PbrPMEI39 or PbrPMEI41, the content of methylesterified pectin at the region 5-20μm from the pollen tube tip significantly increases, and the growth of pear pollen tubes is promoted. These results indicate that PMEI regulates the growth of pollen tubes by changing the distribution of methylesterified pectin in the apex.

Pollen Source Affects Development and Behavioral Preferences in Honey Bees.

Simple SummaryPollinators adjust their foraging preference based on the pollen cues of foraging plants. Honey bees, for example, prefer to collect one type of pollen from plants that bloom at the same time. In northern China, apricot and pear trees are the two main foraging plants in the early spring. However, honey bees tend to collect pollen from apricot trees. It is interesting to understand what affects the foraging decision of honey bees regarding these two pollen types. In this study, we observed the foraging preference of Apis mellifera workers with respect to apricot and pear pollen under laboratory conditions. The effect of pollen on the development of the hypopharyngeal gland (HG) and ovary was measured. The number of visits made to apricot pollen was significantly higher than that to pear pollen. Furthermore, the response of the HG and ovary to these two pollens was different. The development of the HG was significantly affected by pollen diet treatments. However, there was no significant difference in the ovarian development of caged workers supplied with the two different pollen diets. Overall, honey bees showed a significant preference for apricot pollen over pear pollen. Compared with the ovary, the HG of honey bee workers may be more sensitive to pollen nutrition.With the availability of various plants in bloom simultaneously, honey bees prefer to collect some pollen types over others. To better understand pollen’s role as a reward for workers, we compared the digestibility and nutritional value of two pollen diets, namely, pear (Pyrus bretschneideri Rehd.) and apricot (Armeniaca sibirica L.). We investigated the visits, pollen consumption, and pollen extraction efficiency of caged Apis mellifera workers. Newly emerged workers were reared, and the effects of two pollen diets on their physiological status (the development of hypopharyngeal glands and ovaries) were compared. The choice-test experiments indicated a significant preference of A. mellifera workers for apricot pollen diets over pear pollen diets (number of bees landing, 29.5 ± 8.11 and 9.25 ± 5.10, p < 0.001 and pollen consumption, 0.052 ± 0.026 g/day and 0.033 ± 0.013 g/day, p < 0.05). Both pollen diets had comparable extraction efficiencies (67.63% for pear pollen and 67.73% for apricot pollen). Caged workers fed different pollen diets also exhibited similar ovarian development (p > 0.05). However, workers fed apricot pollen had significantly larger hypopharyngeal glands than those fed pear pollen (p < 0.001). Our results indicated that the benefits conferred to honey bees by different pollen diets may influence their foraging preference.

Classification of Germination Images of Pear Pollen Using Random Forest and Convolution Neural Network Models

Verifying pollen germination using microscopic images is a difficult task. It is usually time-consuming and may entail reduced accuracy and reproducibility. Therefore, in this study, we used random forest (RF) and convolutional neural network (CNN) models to perform image classification on raw data corresponding to pollens with different germination rates; the data were obtained via flow cytometry. A heat map, which was based on the RF analysis results, showed that the variables that significantly influenced the classification decision between NG and 60G categories were mainly located in the center and top-right regions of the 30×30 pixel image. Additionally, a variable importance plot showed that among the 900 input variables, pixel_316 was the variable that contributed the most toward prediction. Gradient-weighted class activation mapping was used to visualize the class activation maps of the CNN model. The bottom-left region of the activation map was activated in the NG image. However, the 60G image showed that not only the bottom-left region but also the top-right region was activated. Both the models classified the input images into NG and 60G categories with high accuracy. However, considering that the RF model does not reflect the characteristics of adjacent variables, the CNN model is more appropriate for classifying pollen germination images corresponding to pollen with various germination rates into distinct classes. Taken together, these results suggest that the CNN model can provide a reliable method for verifying the pollen performance.

The Peptide PbrPSK2 From Phytosulfokine Family Induces Reactive Oxygen Species (ROS) Production to Regulate Pear Pollen Tube Growth.

Phytosulfokines (PSKs) are plant peptide growth factors that participate in multiple biological processes, including cell elongation and immune signaling. However, little is known about PSKs in Rosaceae species. Here, we identified 10 PSK genes in pear (Pyrus bretschneideri), 11 in apple (Malus × domestica), four in peach (Prunus persica), six in strawberry (Fragaria vesca), and five in Chinese plum (Prunus mume). In addition, we undertook comparative analysis of the PSK gene family in pear and the four other species. Evolutionary analysis indicated that whole genome duplication events (WGD) may have contributed to the expansion of the PSK gene family in Rosaceae. Transcriptomes, reverse transcription-PCR and quantitative real-time-PCR analyses were undertaken to demonstrate that PbrPSK2 is highly expressed in pear pollen. In addition, by adding purified E. coli-expressed PbrPSK2 to pollen and using an antisense oligonucleotide approach, we showed that PbrPSK2 can promote pear pollen tube elongation in a dose-dependent manner. Furthermore, PbrPSK2 was found to mediate the production of reactive oxygen species to regulate pear pollen tube growth.

PbrPOE21 inhibits pear pollen tube growth in vitro by altering apical reactive oxygen species content.

Genome-wide identification, tissue-specific expression analysis and functional characterization of selected genes containing the pear Pollen Olea europaea I domain reveal their roles in pollen tube growth. Genes containing the Pollen Olea europaea I (POE) domain play crucial roles in diverse growth and developmental processes. Nevertheless, the specific functions of POE family members in progression of pollen tube growth (PTG) remain uncharacterized. We identified 45 PbrPOE genes in the pear (Pyrus bretschneideri) genome, clustered into seven subclasses. PbrPOE genes contained 1 to 11 exons and 0 to 10 introns, with exon/intron structure mostly conserved within each subclass. Whole-genome duplication has mainly contributed to the duplication pattern of PbrPOE genes in pear. Expression profiles of 45 PbrPOE genes in 12 different pear tissues revealed that six PbrPOE genes (PbrPOE6, 12, 21, 29, 35 and 41) of subclass B were highly expressed during the growth of the pear pollen tube in vitro. PbrPOE21 was selected for further functional analysis on the basis of its high and differential expression pattern in pollen. Antisense oligodeoxynucleotide assays demonstrated that PTG was augmented in vitro when PbrPOE21 expression was significantly inhibited. Moreover, pollen tube length in vitro was reduced when PbrPOE21 was transitorily over-expressed using particle bombardment technology. Exogenous PbrPOE21 recombinant protein inhibited PTG in vitro at an optimum concentration of 1.8µM. PbrPOE21 also affected reactive oxygen species content in the pear pollen tube apex. We suggest that PbrPOE21 inhibits PTG in vitro by altering apical reactive oxygen species content.

Troubles in pear pollination: Effects of collection and storage method on pollen viability and fruit production

Pear trees require insect pollination among compatible cultivars to set fruit. However, pollen transfer limitation is the main cause of poor yields in this species, due to low visitation rates and few pollen transfer among compatible cultivars. Assisted pollination using “pollen dispensers” containing precollected compatible pollen fitted into the opening of a beehive could increase yield. We investigated whether stored pollen collected from flowers or bee visitors is suitable for pollinating two European pear (Pyrus communis) cultivars, ‘Conférence’ and ‘Doyenné du Comice’. Pollen collected directly from flowers and indirectly from insects was stored for up to 1 year at 4 °C and −20 °C. Pollen stored at −20 °C showed high viability for both cultivars (60–72%). Consequently, fruit set and fruit diameter using this pollen for pollination was similar to that of fresh pollen. However, the viability of pollen that had been stored at 4 °C was low (6%–14%) and fruit diameter was 6.5% lower when flowers were pollinated with pollen stored at 4 °C compared to fresh pollen. The viability of bee-collected pollen was up to 62% lower than that of pollen collected from flowers. The use of bee-collected pollen as a pollen source resulted in a 48% lower fruit set and 95% lower seed set in ‘Conférence’ compared to fresh pollen, whereas it did not affect ‘Doyenné du Comice’ fruit and seed sets. The fruit diameter was smaller when flowers were pollinated with bee-collected pollen than with fresh pollen in both ‘Conférence’ (54.7 vs. 60.6 mm) and ‘Doyenné du Comice’ (62.5 vs. 70.0 mm). Therefore, pear pollen collected from flowers and stored at −20 °C could successfully be used for alternative pollination without affecting fruit production.

Expression and evolutionary analysis of soluble inorganic pyrophosphatase gene family in pear and four other Rosaceae species

In plants, soluble inorganic pyrophosphatase (PPA) play an indispensable role in inorganic pyrophosphate hydrolysis. However, the expression and the evolutionary history of PPA gene family remain unclear in pear and Rosaceae species. In this study, thirty-nine PPA genes were identified from five Rosaceae species including pear (Pyrus bretschneideri), apple (Malus domestica), peach (Prunus persica), strawberry (Fragaria vesca) and Japanese apricot/mei (Prunus mume). Based on the structural characteristics of the genes and phylogenetic analysis, members of PPA gene family were classified into two main subfamilies (A and B). Whole-genome duplication (WGD) and dispersed gene duplication were the main force, which drove the expansion of PPA gene family in pear and other Rosaceae species. Purifying selection played a dominant role in the evolution of PPA genes. Subcellular localization analysis demonstrated that pear PPA genes located in the cytosol, chloroplasts or near the nuclear envelope. PPA genes showed multiple expression patterns in different pear tissues. Several members of PPA gene family presented particularly higher expression level in only one of the six tissues, such as PbrPPA2, PbrPPA5 and PbrPPA8. Expression analysis showed that five PPA genes were involved in the growth of pear pollen tube, meanwhile four PPA genes could respond to excess of PPi in pear pollen tube. Overall, we established a comprehensive landscape in the functional characterization and evolution of PPA gene family in pear and Rosaceae species, and provided gene expression data for exploring the functional roles of PPA genes in the growth of pear pollen tube.

Supplementation of natural prey with pollen grains exerts an influence on the life table parameters of Neoseiulus californicus.

Better performance of generalist predators, as well as an increase in their density, may be an incentive factor in the ability of the predators to exploit more than one food item or mixed diets. In this study, the effects of four pollen grains (cedar, pear, apricot, and pistachio) when provided to Neoseiulus californicus in mixed diets with prey, Tetranychus urticae, were evaluated. The result indicated that the fastest female developmental time was observed on pistachio pollen + T. urticae, together with apricot pollen + T. urticae. Females reared on the mixed diet comprising pistachio pollen reflected the longest total life span duration, while the shortest total life span was observed in those on the diet that included pear pollen. Furthermore, the lowest fecundity, as well as the shortest reproduction period, was determined on the diets that included pear pollen, while the highest fecundity and the longest reproduction period were observed in pistachio pollen + T. urticae. In addition, the intrinsic (r) and finite rate of increase (λ), net (R0) and gross (GRR) reproductive rates were highest in pistachio pollen + T. urticae. These findings have important implications for developing a comprehensive biological control program of T. urticae, which will be discussed.

Characterization of the pectin methyl-esterase gene family and its function in controlling pollen tube growth in pear (Pyrus bretschneideri)

Pectin methyl-esterases (PMEs) play crucial roles in plant growth. In this study, we identified 81 PbrPMEs in pear. Whole-genome duplication and purifying selection drove the evolution of PbrPME gene family. The expression of 47 PbrPMEs was detected in pear pollen tube, which were assigned to 13 clusters by an expression tendency analysis. One of the 13 clusters presented opposite expression trends towards the changes of methyl-esterified pectins at the apical cell wall. PbrPMEs were localized in the cytoplasm and plasma membrane. Repression of PbrPME11, PbrPME44, and PbrPME59 resulted in the inhibition of pear pollen tube growth and abnormal deposition of methyl-esterified pectins at pollen tube tip. Pharmacological analysis confirmed that reduced PbrPME activities repressed the pollen tube growth. Overall, we have explored the evolutionary characteristics of PbrPME gene family and found the key PbrPME genes that control the growth of pollen tube, which deepened the understanding of pear fertility regulation.

&lt;p class="Body"&gt;&lt;strong&gt;Comparison of different pollen grains and a factitious prey as food sources for &lt;em&gt;Amblyseius swirskii&lt;/em&gt; (Acari: Phytoseiidae)&lt;/strong&gt;&lt;/p&gt;

Pollen used as an alternative or supplementary food source for a predatory mite not only provides important nutrients but also allows the predator to establish a population before prey becomes available. In this study, we compared the pollen of apricot, pear, hollyhock, opium poppy, and date palm, and a factitious prey, UV-irradiated eggs of Ephestia kuehniella, as food sources for Amblyseius swirskii. Different food items affected all development stages differently, except for hollyhock pollen, where eggs failed to develop to maturity. Food type affected the reproductive ability of females, which did not reproduce when fed on opium poppy during immature stages. Most eggs per female were produced when feeding on the factitious prey, and second most with apricot pollen. Feeding on factitious prey compared with pollen, resulted in greater longevity of both female and male adults. Feeding on pear pollen or factitious prey caused, respectively, the lowest and highest population growth rates (r and λ). Both net (R0) and gross (GRR) reproductive rates were highest when the factitious prey was the food source. Among the pollen diets, apricot was the most beneficial food item. Because of their effects on rates of population increase, either apricot pollen or the factitious prey could be further utilized as cost-effective alternative food diets for both experimental and commercial mass rearing of A. swirskii.

A low molecular-weight cyclophilin localizes in different cell compartments of Pyrus communis pollen and is released in vitro under Ca2+ depletion

Cyclophilins (CyPs) are ubiquitous proteins involved in a wide variety of processes including protein maturation and trafficking, receptor complex stabilization, apoptosis, receptor signaling, RNA processing, and spliceosome assembly. The ubiquitous presence is justified by their peptidyl-prolyl cis-trans isomerase (PPIase) activity, catalyzing the rotation of X-Pro peptide bonds from a cis to a trans conformation, a critical rate-limiting step in protein folding, as over 90% of proteins contain trans prolyl imide bonds. In Arabidopsis 35 CyPs involved in plant development have been reported, showing different subcellular localizations and tissue- and stage-specific expression. In the present work, we focused on the localization of CyPs in pear (Pyrus communis) pollen, a model system for studies on pollen tube elongation and on pollen-pistil self-incompatibility response. Fluorescent, confocal and immuno-electron microscopy showed that this protein is present in the cytoplasm, organelles and cell wall, as confirmed by protein fractionation. Moreover, an 18-kDa CyP isoform was specifically released extracellularly when pear pollen was incubated with the Ca2+ chelator EGTA.

Genetic relationship between the ‘Korla fragrant pear’ and local pear varieties in xinjiang based on floral organ characteristics

The characters of floral organ and pollen of local pear varieties in Xinjiang, such as the ‘Korla fragrant pear’ and 39 other varieties or types, Pyrus bretschneideri Rehd., Pyrus pyrifolia Nakai., and Pyrus communis L. were measured and described. The genetic relationships between the ‘Korla fragrant pear’ and other local pear varieties in Xinjiang were analyzed by clustering. The number of flowers per inflorescence of varieties or types was approximately 7.6, and the difference in the number of stamens was small. Except for ‘Aiwenqieke’, ‘Qipanli’ and ‘Daxiangshui’, which had no pollen, the pollen quantity of the varieties or types was 1000.0–5000.0 grains. The pollen grains were isopolar and radiation symmetrical single-grain. The pollen grains had three germination furrows, and the main type of pollen grain exine ornamentation was stripe ornamentation. According to Erdtman’s NPC classification system, the pear pollen was of the N3P4C5 type. According to the clustering results, there was high similarity between the ‘Korla fragrant pear’ and Pyrus sinkiangensis Yü. The ‘Korla fragrant pear’ clustered with most local varieties in Xinjiang, and a genetic relationship between P. bretschneideri and P. pyrifolia was observed. There were interspecific and variety or type differences in floral organ and pollen morphology between P. sinkiangensis and P. bretschneideri, P. pyrifolia, Pyrus ussuriensis Maxim., P. communis and Pyrus betulifolia Bunge. There were many similarities between the ‘Korla fragrant pear’ and local pear varieties in Xinjiang, which should be classified within the P. sinkiangensis system.

Metacaspase gene family in Rosaceae genomes: Comparative genomic analysis and their expression during pear pollen tube and fruit development.

Metacaspase (MC), which is discovered gene family with distant caspase homologs in plants, fungi, and protozoa, may be involved in programmed cell death (PCD) processes during plant development and respond abiotic and biotic stresses. To reveal the evolutionary relationship of MC gene family in Rosaceae genomes, we identified 8, 7, 8, 12, 12, and 23 MC genes in the genomes of Fragaria vesca, Prunus mume, Prunus persica, Pyrus communis, Pyrus bretschneideri and Malus domestica, respectively. Phylogenetic analysis suggested that the MC genes could be grouped into three clades: Type I*, Type I and Type II, which was supported by gene structure and conserved motif analysis. Microsynteny analysis revealed that MC genes present in the corresponding syntenic blocks of P. communis, P. bretschneideri and M. domestica, and further suggested that large-scale duplication events play an important role in the expansion of MC gene family members in these three genomes than other Rosaceae plants (F. vesca, P. mume and P. persica). RNA-seq data showed the specific expression patterns of PbMC genes in response to drought stress. The expression analysis of MC genes demonstrated that PbMC01 and PbMC03 were able to be detected in all four pear pollen tubes and seven fruit development stages. The current study highlighted the evolutionary relationship and duplication of the MC gene family in these six Rosaceae genomes and provided appropriate candidate genes for further studies in P. bretschneideri.

Changes in the Activity of Peroxidase and Dehydrogenase in Pear Pollen During Germination under Different Storage Conditions

Changes in the Activity of Peroxidase and Dehydrogenase in Pear Pollen During Germination under Different Storage Conditions

Proteome analysis reveals a strong correlation between olfaction and pollen foraging preference in honeybees

To gain a deeper understanding of the molecular basis of pollen foraging preference, we characterized the proteomes of antennae and brains of bees foraging on pear and rapeseed flowers, and the volatile compounds from nectar, anther, and inflorescence of both plants. Bees foraging on the pollen of the two plants have shaped the distinct proteome arsenals in the antenna and brain to drive olfactory and brain function. In antennae, bees foraging on pear (PA) pollen pathways associated with protein metabolism were induced to synthesize new proteins for modulation of synaptic structures via stabilizing and consolidating specific memory traces. Whereas, bees foraging on rapeseed (BA) pollen pathways implicated in energy metabolism were activated to provide metabolic fuels critical for neural activity. These findings suggest that the distinct biochemical route is functionally enhanced to consolidate the divergent olfaction in PA and BA. In brain, although the uniquely induced pathways in bees forging on both plants are likely to cement selective roles in learning and memory, pollen foraging preference in bees is mainly drived by olfaction. Furthermore, both plants have shaped different repertoires of signal odors and food rewards to attract pollinators. The suggested markers are potentially useful for selection of bees to improve their olfaction for better pollination of the plants.

Pollen trapping and sugar syrup feeding of honey bee (Hymenoptera: Apidae) enhance pollen collection of less preferred flowers.

Pear (Pyrus bretschneideri) is characterized by being self-incompatible and dependent on cross-pollination to set fruit. Honeybee (Apis mellifera) is considered the most important pollinator of pear. Nevertheless, limited pollen transfer has been cited as the main cause of poor fruit set in many pear orchards. Here, we tested the following hypotheses: (i) colony manipulations increase the pollen collection tendency of honeybees and (ii) the proportion of pollen loads being returned to the hive is from the target plant. The technique reliably and rapidly estimates the pollination of honeybees tested under different colony manipulations: (1) using pollen trapping (PT); (2) PT with sugar syrup feeding (SS) (PTSS); (3) SS alone and (4) control without PT and SS. The results clearly show that the pollen collection of honeybees during the experiment was significantly affected (P < 0.05) by colony manipulations. The mean amount of pollen harvested daily was higher for PTSS (19.4 g) and PT (16.4 g) than for SS (12.85 g) and control (8.7 g) colonies. Therefore, PTSS was the most effective treatment for increasing pear pollen collection; other treatments such as PT and SS could also be useful. This study was important for determining how the behavior of honeybee colonies is shaped through colony manipulation to enhance pollen collection of less preferred pear flowers, which is critical when pollination is required.

PbGLR3.3 Regulates Pollen Tube Growth in the Mediation of Ca2+ Influx in Pyrus bretschneideri

Glutamate receptors (GluRs) are sensors of extracellular signals; they play important roles in the regulation of multiple physiological and developmental processes in eukaryotes. However, their functional roles in fruit trees are largely unknown. Here, based on the pear genome database, which was established in this lab, we identified 34 PbGLRs in pear (Pyrus bretschneideri Rehd), and they were divided into four groups by phylogenetic analysis. In comparisons with other groups, phylogenetic analyses and structural information of the PbGLRs in group 3 suggest that these genes underlie specific characteristics. Among the ten genes in group 3, we observed that the expression of PbGLR3.3 increased gradually during pollen germination and continuous growth, indicating that this gene might play a vital role in the development of pear pollen tubes. Using a combination of antisense oligodeoxy nucleotides and Ca2+-sensitive fluorescent probe methods, we verified that PbGLR3.3 participates in DSer-elicited intracellular Ca2+ signaling and Ca2+ regulation of growth in pear pollen tubes.

ALA inhibits pear pollen tube growth through regulation of vesicle trafficking

Abstract 5-Aminolevunic acid, a natural plant growth regulator, can thin pear fruits by inhibiting pollen tube growth through Ca2+-ATPase-mediated Ca2+ efflux. Here, using a non-invasive micromeasurement technology, we detected the occurrence of an ALA-induced Ca2+ efflux. Transmission electron microscope observations showed that a disruption of the intracellular Ca pool, including endoplasmic reticulum and mitochondria, was also linked to ALA-decreased Ca2+ in pollen tubes. Then we further explored the mechanisms how ALA-decreased Ca2+ inhibits pollen tube growth. We observed that ALA-inhibited pollen tube growth was accompanied by tube swelling and disruption in an ALA concentration-dependent manner. Ultrastructural studies further showed that ALA increased the number of vesicles, and the vesicle aggregation resulted in the morphological abnormality of pollen tubes. Confocal laser scanning microscopy using the fluorescent marker FM 4-64 confirmed the increasing number of vesicles induced by ALA in the pollen tubes. Ultrastructural analysis of pollen tubes treated by ALA with exogenous CaCl2 or/ and EGTA not only indicated that a Ca2+ signal plays a crucial role in ALA-mediated increase of vesicles, but also suggested that destruction of endoplasmic reticulum and Golgi bodies is one of the vesicle sources. Confocal microscopy of FM 4-64 further demonstrated that Ca2+ signal involves in ALA-mediated increase of vesicles also through promoting endocytosis and inhibiting exocytosis. In addition, treatment of taxol, a microtubule stabilizer, partially rescued the effects of ALA on pollen tube growth and FM 4-64 staining, indicating that microtubules are involved in ALA-regulated pollen tube growth. Taken together, we conclude that ALA-decreased Ca2+ disrupts endoplasmic reticulum and Golgi apparatus, enhances endocytosis, suppresses exocytosis, impairs vesicle transport, and finally leads to vesicle accumulation and abnormality of pollen tubes. Our findings provide new information on how ALA regulates pollen tube growth.

The unique evolutionary pattern of the Hydroxyproline-rich glycoproteins superfamily in Chinese white pear (Pyrus bretschneideri)

BackgroundThe hydroxyproline-rich glycoprotein (HRGP) superfamily, comprising three families (arabinogalactan-proteins, AGPs; extensins, EXTs; proline-rich proteins, PRPs), is a class of proline-rich proteins that exhibit high diversity and are involved in many aspects of plant biology.ResultsIn this study, 838 HRGPs were identified from Chinese white pear (Pyrus bretschneideri) by searching for biased amino acid composition and conserved motifs. 405 HRGPs were derived from whole genome duplication (WGD) events which is suggested to be the major force of driving HRGPs expansion and the recent WGD event shared by apple and pear generated most duplicated HRGPs in pear. This duplication event drived the structural variation of the HRGPs encoding hydroxyproline (Hyp)-rich motifs. The rate of HRGPs evolution mainly impacted the Hyp-rich motifs even in chimeric HRGPs. During the evolution of 53 PRPs that are also typified by 7-deoxyloganetin glucosyltransferase-like genes, the duplication from PRP to non-PRP was indirectly modified by positive selection. These results suggested that the rate of HRGP evolution mainly influenced the Hyp-rich motifs even in chimeric HRGPs. The expression divergence of HRGPs was higher than that of other commonly duplicated genes. In pear pistil, 601 HRGPs exhibited expression, while in pear pollen, 285 HRGPs were expressed. The qPCR results revealed that Pbr036330.1 and Pbr010506.1 showed different expression profile in self-incompatibility of pear pistil.ConclusionsThe researches indicated that WGD events was the main duplication type during the evolution of HRGPs, and the highly variable Hyp-motifs might be accountable for the expansion, evolution and expression divergence of HRGPs and that this divergence may be responsible for the gain of new functions in plants.