Characterization of Five Meloidogyne incognita Effectors Associated with PsoRPM3.

Root-knot nematodes (RKNs) are devastating parasites that invade thousands of plants. In this study, five RKN effectors, which might interact with Prunussogdiana resistance protein PsoRPM3, were screened and identified. In situ hybridisation results showed that MiCal, MiGST_N_4, MiEFh and MiACPS are expressed in the subventral oesophageal glands (SvG), and MiTSPc hybridization signals are found in the dorsal esophageal gland (DG) of Meloidogyne incognita in the pre-J2. RT-qPCR data indicated that the expression of MiCal, MiGST_N_4, MiEFh, and MiACPS genes are highly expressed in M. incognita of pra-J2 and J3/J4 stages. The expression of MiTSPc increased significantly in the female stage of M. incognita. Moreover, all effectors found in this study localize in the cytoplasm and nucleus when transiently expressed in plant cells. In addition, MiGST_N_4, MiEFh, MiACPS and MiTSPc can elicit the ROS burst and strong hypersensitive response (HR), as well as significant ion leakage. Our data suggest that MiGST_N_4, MiEFh, MiACPS and MiTSPc effectors may be involved in triggering the immune response of the host plant.

Integrated Analysis of the Metabolome and Transcriptome on Anthocyanin Biosynthesis in Four Developmental Stages of Cerasus humilis Peel Coloration.

Cerasus humilis is a unique dwarf shrub and fruit color is an important trait in the species. In this study, we evaluated the transcriptomic and metabolomic profiles of the plant at different developmental stages to elucidate the mechanism underlying color formation. In a metabolomics analysis, 16 anthocyanin components were identified at four developmental stages, and high levels of cyanidin O-syringic acid and pelargonidin 3-O-beta-d-glucoside (callitephin chloride) were correlated with the reddening of the fruit peel. A co-expression analysis revealed that ANS and UFGT play key roles in pigmentation (PCC > 0.82). Additionally, transcriptome data showed that most anthocyanin biosynthetic genes and two MYB transcription factors were significantly up-regulated. QRT-PCR results for these differentially expressed genes were generally consistent with the high-throughput sequencing. Moreover, the overexpression of ChMYB1 (TRINITY_DN21536_c0_g1) in apple calli could contribute to the accumulation of anthocyanin. It was also found that UFGT (TRINITY_DN19893_c1_g5) and ChMYB1 (TRINITY_DN21536_c0_g1) have similar expression patterns. These findings provide insight into the mechanisms underlying anthocyanin accumulation and coloration during fruit peel development, providing a basis for the breeding of anthocyanin-rich C. humilis cultivars.

Comparative transcriptome analysis reveals the molecular regulation underlying the adaptive mechanism of cherry (Cerasus pseudocerasus Lindl.) to shelter covering.

BACKGROUND: Rain-shelter covering is widely applied during cherry fruit development in subtropical monsoon climates with the aim of decreasing the dropping and cracking of fruit caused by excessive rainfall. Under rain-shelter covering, the characteristics of the leaves and fruit of the cherry plant may adapt to the changes in the microclimate. However, the molecular mechanism underlying such adaptation remains unclear, although clarifying it may be helpful for improving the yield and quality of cherry under rain-shelter covering. RESULTS: To better understand the regulation and adaptive mechanism of cherry under rain-shelter covering, 38,621 and 3584 differentially expressed genes were identified with a combination of Illumina HiSeq and single-molecule real-time sequencing in leaves and fruits, respectively, at three developmental stages. Among these, key genes, such as those encoding photosynthetic-antenna proteins (Lhca and Lhcb) and photosynthetic electron transporters (PsbP, PsbR, PsbY, and PetF), were up-regulated following the application of rain-shelter covering, leading to increased efficiency of light utilization. The mRNA levels of genes involved in carbon fixation, namely, rbcL and rbcS, were clearly increased compared with those under shelter-free conditions, resulting in improved CO2 utilization. Furthermore, the transcription levels of genes involved in chlorophyll (hemA, hemN, and chlH) and carotenoid synthesis (crtB, PDS, crtISO, and lcyB) in the sheltered leaves peaked earlier than those in the unsheltered leaves, thereby promoting organic matter accumulation in leaves. Remarkably, the expression levels of key genes involved in the metabolic pathways of phenylpropanoid (PAL, C4H, and 4CL) and flavonoid (CHS, CHI, F3'H, DFR, and ANS) in the sheltered fruits were also up-regulated earlier than of those in the unsheltered fruits, conducive to an increase in anthocyanin content in the fruits. CONCLUSIONS: According to the physiological indicators and transcriptional expression levels of the related genes, the adaptive regulation mechanism of cherry plants was systematically revealed. These findings can help understand the effect of rain-shelter covering on Chinese cherry cultivation in rainy regions.

The complete genome sequence of Rahnella aquatilis ZF7 reveals potential beneficial properties and stress tolerance capabilities.

Rahnella aquatilis ZF7 is a plant beneficial strain isolated from Sakura tree soil with potential for biocontrol. Here, we present the complete genome sequence of R. aquatilis ZF7, which consists of one 4.49 Mb circular chromosome and a 54-kb plasmid named pRAZF7. Phylogenetic analyses revealed that R. aquatilis ZF7 is much similar to the strains Rahnella sp. Y9602 and R. aquatilis HX2 than others evaluated. In this study, multiple genes encoding functions that likely contribute to plant growth promotion, biocontrol and stress tolerance were identified by comparative genome analyses, including IAA production, phosphate solubilization, antibiotic resistance and formation of Se nanoparticles (SeNPs). In addition, these functions were also confirmed by in vitro experiments. Considering its ability to form SeNPs, strain R. aquatilis ZF7 will contribute to nano-agriculture. Overall, the features of R. aquatilis ZF7 make it a high potential and competitive strain in biocontrol, and the genome data will help further studies on the mechanisms of plant growth promotion and biocontrol.

Molecular Bases of Fruit Quality in Prunus Species: An Integrated Genomic, Transcriptomic, and Metabolic Review with a Breeding Perspective.

In plants, fruit ripening is a coordinated developmental process that requires the change in expression of hundreds to thousands of genes to modify many biochemical and physiological signal cascades such as carbohydrate and organic acid metabolism, cell wall restructuring, ethylene production, stress response, and organoleptic compound formation. In Prunus species (including peaches, apricots, plums, and cherries), fruit ripening leads to the breakdown of complex carbohydrates into sugars, fruit firmness reductions (softening by cell wall degradation and cuticle properties alteration), color changes (loss of green color by chlorophylls degradation and increase in non-photosynthetic pigments like anthocyanins and carotenoids), acidity decreases, and aroma increases (the production and release of organic volatile compounds). Actually, the level of information of molecular events at the transcriptional, biochemical, hormonal, and metabolite levels underlying ripening in Prunus fruits has increased considerably. However, we still poorly understand the molecular switch that occurs during the transition from unripe to ripe fruits. The objective of this review was to analyze of the molecular bases of fruit quality in Prunus species through an integrated metabolic, genomic, transcriptomic, and epigenetic approach to better understand the molecular switch involved in the ripening process with important consequences from a breeding point of view.

Transcriptomic and metabolomic profiling provide novel insights into fruit development and flesh coloration in Prunus mira Koehne, a special wild peach species.

BACKGROUND: Flesh color is one of the most important traits for the commercial value of peach fruit. To unravel the underlying regulatory network in Prunus mira, we performed an integrated analysis of the transcriptome and metabolome of 3 fruit types with various flesh pigmentations (milk-white, yellow and blood) at 3 developmental stages (pit-hardening, cell enlargement and fruit ripening). RESULTS: Transcriptome analysis showed that an intense transcriptional adjustment is required for the transition from the pit-hardening to the cell enlargement stage. In contrast, few genes were differentially expressed (DEGs) from the cell enlargement to the fruit ripening stage and importantly, the 3 fruits displayed diverse transcriptional activities, indicating that difference in fruit flesh pigmentations mainly occurred during the ripening stage. We further investigated the DEGs between pairs of fruit types during the ripening stage and identified 563 DEGs representing the 'core transcriptome' associated with major differentiations between the 3 fruit types, including flesh pigmentation. Meanwhile, we analyzed the metabolome, particularly, at the ripening stage and uncovered 40 differential metabolites ('core metabolome') between the 3 fruit types including 5 anthocyanins, which may be the key molecules associated with flesh coloration. Finally, we constructed the regulatory network depicting the interactions between anthocyanins and important transcripts involved in fruit flesh coloration. CONCLUSIONS: The major metabolites and transcripts involved in fruit flesh coloration in P. mira were unraveled in this study providing valuable information which will undoubtedly assist in breeding towards improved fruit quality in peach.

Changes of pollen viability of ornamental plants after long-term preservation in a cryopreservation pollen bank.

This study determined the changes in pollen viability of 102 species/cultivars of ornamental plants (affiliated to 32 genera of 14 families) following long-term liquid nitrogen storage in a cryopreservation pollen bank. The goal was to provide information on the safety and stability of pollen cryopreservation technology. Fresh pollen at the time of storage was used as the control, and the study examined the pollen viability of ornamental plants cryopreserved for 8, 9, or 10 years. The results show that pollen of the 102 species/cultivars in the cryopreservation pollen bank retained viability ranging from 1% to 58%, After long-term storage there were changes in viability: 11.76% (12 species/cultivars) had increased viability, 16.67% (17 species/cultivars) had stable viability, and the viability of 71.57% (73 species/cultivars) showed a decreasing trend.

The role of miR319a and its target gene TCP4 in the regulation of pistil development in Prunus mume.

The microRNAs (miRNAs) comprise a broad class of non-coding small endogenous RNAs that are associated with many biological processes through the regulation of target genes, such as leaf morphogenesis and polarity, biotic and abiotic stress responses, and root and flower development. We identified a miRNA that affects flower development, miR319a, in Prunus mume. The Pm-miR319a target, Pm-TCP4, was validated by 5'RACE. The higher expression of Pm-TCP4 in imperfect flowers showed that Pm-TCP4 might promote pistil abortion. Further experiments showed that Pm-miR319a negatively regulates the expression of Pm-TCP4 mRNAs and affected pistil development. Sixteen downstream genes of Pm-TCP4 related to flower development were predicted. Previous studies have shown that they have an impact on the development of pistils. In this study it was established that Pm-miR319a indirectly regulates the development of pistils by regulating its target gene Pm-TCP4.

Light energy partitioning, photosynthetic efficiency and biomass allocation in invasive Prunus serotina and native Quercus petraea in relation to light environment, competition and allelopathy.

This study addressed whether competition under different light environments was reflected by changes in leaf absorbed light energy partitioning, photosynthetic efficiency, relative growth rate and biomass allocation in invasive and native competitors. Additionally, a potential allelopathic effect of mulching with invasive Prunus serotina leaves on native Quercus petraea growth and photosynthesis was tested. The effect of light environment on leaf absorbed light energy partitioning and photosynthetic characteristics was more pronounced than the effects of interspecific competition and allelopathy. The quantum yield of PSII of invasive P. serotina increased in the presence of a competitor, indicating a higher plasticity in energy partitioning for the invasive over the native Q. petraea, giving it a competitive advantage. The most striking difference between the two study species was the higher crown-level net CO2 assimilation rates (Acrown) of P. serotina compared with Q. petraea. At the juvenile life stage, higher relative growth rate and higher biomass allocation to foliage allowed P. serotina to absorb and use light energy for photosynthesis more efficiently than Q. petraea. Species-specific strategies of growth, biomass allocation, light energy partitioning and photosynthetic efficiency varied with the light environment and gave an advantage to the invader over its native competitor in competition for light. However, higher biomass allocation to roots in Q. petraea allows for greater belowground competition for water and nutrients as compared to P. serotina. This niche differentiation may compensate for the lower aboveground competitiveness of the native species and explain its ability to co-occur with the invasive competitor in natural forest settings.

Simple method to detect year-to-year variability of blooming phenology of Cerasus × yedoensis by digital camera.

The year-to-year variability of the blooming phenology of cherry trees is important as a proxy climate indicator and strongly affects cultural ecosystem services. Observation of blooming phenology at multiple points requires a simple and flexible approach. We examined changes in the canopy gap fraction extracted from binarized upward images taken periodically beneath a Cerasus × yedoensis 'Somei-yoshino' tree. The gap fraction decreased rapidly after the start of bloom, reached a minimum value at full bloom, and began to increase again, but then decreased rapidly during leaf flush. These changes reflect the phenology of blooming and leaf flush after flower drop of 'Somei-yoshino'. These characteristics allow detection of the year-to-year variability of the bloom and leaf-flush phenology of cherry and other deciduous tree species that show the same patterns.

Heat treatment as postharvest tool for improving quality in extra-early nectarines.

BACKGROUND: Extra-early nectarine cultivars such as 'VioWhite 5' could present a lack of organoleptic and nutritional quality. Heat treatments (HT) can be applied to improve their primary characteristics. In this experiment, control (non-treated), HT1 (3 h; 45 °C) and HT2 (2 h; 50 °C) were studied. Fruit were stored (10 days; 0 ± 0.5 °C; 90-95% RH) followed by a simulated retail sale period (3 days; 15 °C; 70-75% RH). RESULTS: HT fruit showed higher weight loss (2.76 ± 0.06% and 3.32 ± 0.01% for HT1 and HT2 , respectively; vs. 2.23 ± 0.14% for control) and lower firmness than control samples (28.88% and 21.67% less for HT1 and HT2 , respectively). HT treatments induced an increase in soluble solids content and a decrease in total acidity, which led to a better sensory quality. These changes were positively received by consumers. Total antioxidant capacity was enhanced by HT due to an increase in phenolic compound content. A higher enzymatic activity was found in pectin methylesterase and polygaracturonase in HT nectarines when compared to control. CONCLUSION: The application of HT on extra-early nectarine cv. demonstrated a strong potential to improve consumption quality in the industry. © 2017 Society of Chemical Industry.

SEP-class genes in Prunus mume and their likely role in floral organ development.

BACKGROUND: Flower phylogenetics and genetically controlled development have been revolutionised during the last two decades. However, some of these evolutionary aspects are still debatable. MADS-box genes are known to play essential role in specifying the floral organogenesis and differentiation in numerous model plants like Petunia hybrida, Arabidopsis thaliana and Antirrhinum majus. SEPALLATA (SEP) genes, belonging to the MADS-box gene family, are members of the ABCDE and quartet models of floral organ development and play a vital role in flower development. However, few studies of the genes in Prunus mume have yet been conducted. RESULTS: In this study, we cloned four PmSEPs and investigated their phylogenetic relationship with other species. Expression pattern analyses and yeast two-hybrid assays of these four genes indicated their involvement in the floral organogenesis with PmSEP4 specifically related to specification of the prolificated flowers in P. mume. It was observed that the flower meristem was specified by PmSEP1 and PmSEP4, the sepal by PmSEP1 and PmSEP4, petals by PmSEP2 and PmSEP3, stamens by PmSEP2 and PmSEP3 and pistils by PmSEP2 and PmSEP3. CONCLUSION: With the above in mind, flower development in P. mume might be due to an expression of SEP genes. Our findings can provide a foundation for further investigations of the transcriptional factors governing flower development, their molecular mechanisms and genetic basis.

Light conditions affect the performance of Yponomeuta evonymellus on its native host Prunus padus and the alien Prunus serotina.

The bird cherry ermine moth, Yponomeuta evonymellus L., is considered an obligatory monophagous insect pest that feeds only on native European Prunus padus L. In recent years, however, increased larval feeding on alien P. serotina Ehrh. has been observed. In both species, general defoliation is extensive for shade grown trees, whereas it is high in P. padus, but very low in P. serotina, when trees are grown in full light conditions. The aim of the present study was to identify how the plant host species and light conditions affect the performance of Y. evonymellus. The influence of host species and light condition on their growth and development, characterized by the parameters of pupation, adult eclosion, body mass, potential fecundity, and wing size, was measured in a 2 × 2 experimental design (two light treatments, two hosts). In comparison with high light (HL) conditions, a greater percentage of pupation and a longer period and less dynamic adult emerge was observed under low light (LL) conditions. The effect of host species on these parameters was not significant. In contrast, mass, fecundity and all of the studied wing parameters were higher in larvae that grazed on P. padus than on P. serotina. Similarly the same parameters were also higher on shrubs in HL as compared with those grown under LL conditions. In general, light conditions, rather than plant species, were more often and to a greater extent, responsible for differences in the observed parameters of insect development and potential fecundity.

Phenological model of bird cherry Padus racemosa with data assimilation.

The accuracy of the operational models can be improved by using observational data to shift the model state in a process called data assimilation. Here, a data assimilation approach using the temperature similarity to control the extent of extrapolation of point-like phenological observations is explored. A degree-day model is used to describe the spring phenology of the bird cherry Padus racemosa in the Baltic region in 2014. The model results are compared to phenological observations that are expressed on a continuous scale based on the BBCH code. The air temperature data are derived from a numerical weather prediction (NWP) model. It is assumed that the phenology at two points with a similar temperature pattern should be similar. The root mean squared difference (RMSD) between the time series of hourly temperature data over a selected time interval are used to measure the temperature similarity of any two points. A sigmoidal function is used to scale the RMSD into a weight factor that determines how the modelled and observed phenophases are combined in the data assimilation. The parameter space for determining the weight of observations is explored. It is found that data assimilation improved the accuracy of the phenological model and that the value of the point-like observations can be increased through using a weighting function based on environmental parameters, such as temperature.

Variability of growing degree days in Poland in response to ongoing climate changes in Europe.

An observed increase in air temperature can lead to significant changes in the phenology of plants and, consequently, changes in agricultural production. The aim of the study was to evaluate the spatial differentiation of thermal resources in Poland and their variability during a period of changing thermal conditions in Europe. Since the variability of thermal conditions is of paramount importance for perennial crops, the study focused on apple, plum, and cherry orchard regions in Poland. The analysis was conducted for the period of 1951-2010 using air temperature daily data. Thermal resources have been defined using the growing degree days (GDD) index calculated independently for the whole year and during in frost-free season for three air temperature thresholds: 0, 5, and 10 °C, which determine the non-winter period, growing season, and the period of full plant growth, respectively. In addition, due to the high significance for perennials in particular, the incidence and intensity of frost during flowering were calculated. In this study, a detailed analysis of the spatial differentiation of thermal resources was first performed, followed by an evaluation of long-term variability and associated change patterns. The obtained results confirmed an increase in thermal resources in Poland as a consequence of the lengthening of the growing season. However, the frequency and intensity of spring frost, especially during flowering or even during ripening of plants, remain a threat to harvests in both the eastern and western parts of the country.

Thinned stone fruits are a source of polyphenols and antioxidant compounds.

BACKGROUND: Thinned fruits are agricultural by-products that contain large quantities of interesting compounds due to their early maturity stage. In this work, the phenolic profile and the antioxidant activity of six thinned stone fruits (apricot, cherry, flat peach, peach, plum and nectarine) have been investigated, focussing on proanthocyanidins. RESULTS: Thinned nectarine had the highest content of total phenols [67.43 mg gallic acid equivalents (GAE) g-1 dry weight (DW)] and total flavonoids (56.97 mg CE g-1 DW) as well as the highest antioxidant activity measured by DPPH scavenging (133.30 mg [Trolox equivalents (TE) g-1 DW] and FRAP assay (30.42 mg TE g-1 DW). Proanthocyanidins were very abundant in these by-products, and the main phenolic group quantified in cherry (10.54 mg g-1 DW), flat peach (33.47 mg g-1 DW) and nectarine (59.89 mg g-1 DW), while hydroxycinnamic acids predominate in apricot, peach and plum (6.67, 22.04 and 23.75 mg g-1 DW, respectively). The low, mean degree of polymerisation of proanthocyanidins suggests that their bioavailability could be very high. CONCLUSIONS: This study shows that thinned stone fruit extracts might be used as antioxidants in foods or as a source of compounds with health-related benefits that can be used in the pharmaceutical, cosmetic and food industries. © 2016 Society of Chemical Industry.

Seed trait-mediated selection by rodents affects mutualistic interactions and seedling recruitment of co-occurring tree species.

As mutualists, seed dispersers may significantly affect mutualistic interactions and seedling recruitment of sympatric plants that share similar seed dispersers, but studies are rare. Here, we compared seed dispersal fitness in two co-occurring plant species (Armeniaca sibirica and Amygdalus davidiana) that inhabit warm temperate deciduous forest in northern China. We tested the hypothesis that seed trait-mediated selection by rodents may influence mutualistic interactions with rodents and then seedling establishment of co-occurring plant species. A. davidiana seeds are larger and harder (thick endocarps) than A. sibirica seeds, but they have similar levels of nutrients (crude fat, crude protein), caloric value and tannin. More A. sibirica seedlings are found in the field. Semi-natural enclosure tests indicated that the two seed species were both harvested by the same six rodent species, but that A. sibirica had mutualistic interactions (scatter hoarding) with four rodent species (Apodemus peninsulae, A. agrarius, Sciurotamias davidianus, Tamias sibiricus), and A. davidiana with only one (S. davidianus). Tagged seed dispersal experiments in the field indicated that more A. sibirica seeds were scatter-hoarded by rodents, and more A. sibirica seeds survived to the next spring and became seedlings. A. sibirica seeds derive more benefit from seed dispersal by rodents than A. davidiana seeds, particularly in years with limited seed dispersers, which well explained the higher seedling recruitment of A. sibirica compared with that of A. davidiana under natural conditions. Our results suggest that seed dispersers may play a significant role in seedling recruitment and indirect competition between co-occurring plant species.

GENETIC DIVERSITY OF SOME IRANIAN SWEET CHERRY (PRUNUS AVIUM) CULTIVARS USING MICROSATELLITE MARKERS AND MORPHOLOGICAL TRAITS.

The aim of this study was to characterize 23 important Iranian sweet cherry (Prunus avium) cultivars collected from different provinces of Iran and 1 foreign cultivar, which was used as control, considered for breeding programs by using 21 microsatellite markers and 27 morphological traits. In sweet cherry (Prunus avium) accessions, leaf, fruit, and stone morphological characters were evaluated during two consecutive years. The study revealed a high variability in the set of evaluated sweet cherry accessions. The majority of important correlations were determined among variables representing fruit and leaf size and variables related to color. Cluster analysis distinguished sweet cherry accessions into two distinct groups. Principal component analysis (PCA) of qualitative and quantitative morphological parameters explained over 86.59% of total variability in the first seven axes. In PCA, leaf traits such as leaf length and width, and fruit traits such as length, width, and weight, and fruit flesh and juice color were predominant in the first two components, indicating that they were useful for the assessment of sweet cherry germplasm characterization. Out of 21 SSR markers, 16 were polymorphic, producing 177 alleles that varied from 4 to 16 alleles (9.35 on average) with a mean heterozygosity value of 0.82 that produced successful amplifications and revealed DNA polymorphisms. Allele size varied from 95 to 290 bp. Cluster analyses showed that the studied sweet cherry genotypes were classified intofive main groups based mainly on their species characteristics and SSR data. In general, our results did not show a clear structuring of genetic variability within the Iranian diffusion area of sweet cherry, so it was not possible to draw any indications on regions of provenance delimitation. The results of this study contribute to a better understanding of sweet cherry genetic variations in Iran, thus making for more efficient programs aimed at preserving biodiversity and more rational planning of the management of reproductive material.

Genome-wide analysis of the GRAS gene family in Prunus mume.

Prunus mume is an ornamental flower and fruit tree in Rosaceae. We investigated the GRAS gene family to improve the breeding and cultivation of P. mume and other Rosaceae fruit trees. The GRAS gene family encodes transcriptional regulators that have diverse functions in plant growth and development, such as gibberellin and phytochrome A signal transduction, root radial patterning, and axillary meristem formation and gametogenesis in the P. mume genome. Despite the important roles of these genes in plant growth regulation, no findings on the GRAS genes of P. mume have been reported. In this study, we discerned phylogenetic relationships of P. mume GRAS genes, and their locations, structures in the genome and expression levels of different tissues. Out of 46 identified GRAS genes, 45 were located on the 8 P. mume chromosomes. Phylogenetic results showed that these genes could be classified into 11 groups. We found that Group X was P. mume-specific, and three genes of Group IX clustered with the rice-specific gene Os4. We speculated that these genes existed before the divergence of dicotyledons and monocotyledons and were lost in Arabidopsis. Tissue expression analysis indicated that 13 genes showed high expression levels in roots, stems, leaves, flowers and fruits, and were related to plant growth and development. Functional analysis of 24 GRAS genes and an orthologous relationship analysis indicated that many functioned during plant growth and flower and fruit development. Our bioinformatics analysis provides valuable information to improve the economic, agronomic and ecological benefits of P. mume and other Rosaceae fruit trees.

Transition from two to one integument in Prunus species: expression pattern of INNER NO OUTER (INO), ABERRANT TESTA SHAPE (ATS) and ETTIN (ETT).

While gymnosperm ovules have one integument, in most angiosperms two integuments surround the ovules. Unitegmic ovules have arisen independently several times during the evolution of angiosperms, but the ultimate genetic cause of the presence of a single integument remains elusive. We compared species of the genus Prunus that have different numbers of integuments: bitegmic species, such as Prunus armeniaca (apricot) and Prunus persica (peach), and unitegmic species, such as Prunus incisa, analyzing the expression pattern of genes that are involved in integument development in Arabidopsis thaliana: INNER NO OUTER (INO), ABERRANT TESTA SHAPE (ATS) and ETTIN (ETT). Bitegmic and unitegmic species showed similar INO expression patterns, indicative of the conservation of an outer integument. However, expression of ETT, which occurs in the boundary of the outer and inner integuments, was altered in unitegmic ovules, which showed lack of ETT expression. These results strongly suggest that the presence of a single integument could be attributable to the amalgamation of two integuments and support the role of ETT in the fusion of the outer and inner integuments in unitegmic ovules, a situation that could be widespread in other unitegmic species of angiosperms.