Glycinebetaine mitigates drought stress-induced oxidative damage in pears.

Glycinebetaine (GB) is an osmoprotectant found in plants under environmental stresses that incorporates drought and is associated with drought tolerance in several plants, such as the woody pear. However, how GB improves drought tolerance in pears remains unclear. In the current study, we explored the mechanism by which GB enhances drought tolerance of whole pear plants (Pyrus bretschneideri Redh. cv. Suli) supplied with exogenous GB. The results showed that on the sixth day after withholding water, levels of O2·-, H2O2, malonaldehyde (MDA) and electrolyte leakage in the leaves were substantially increased by 143%, 38%, 134% and 155%, respectively. Exogenous GB treatment was substantially reduced O2·-, H2O2, MDA and electrolyte leakage (38%, 24%, 38% and 36%, respectively) in drought-stressed leaves. Furthermore, exogenous GB induced considerably higher antioxidant enzyme activity in dry-stressed leaves than drought-stressed treatment alone on the sixth day after withholding water, such as superoxide dismutase (SOD) (201%) and peroxidase (POD) (127%). In addition, these GB-induced phenomena led to increased endogenous GB levels in the leaves of the GB 100 + drought and GB 500 + drought treatment groups by 30% and 78%, respectively, compared to drought treatment alone. The findings obtained were confirmed by the results of the disconnected leaf tests, in which GB contributed to a substantial increase in SOD activity and parallel dose- and time-based decreases in MDA levels. These results demonstrate that GB-conferred drought resistance in pears may be due in part to minimizing symptoms of oxidative harm incurred in response to drought by the activities of antioxidants and by reducing the build-up of ROS and lipid peroxidation.

Genome-wide identification and characterization of bZIP transcription factors and their expression profile under abiotic stresses in Chinese pear (Pyrus bretschneideri).

BACKGROUND: In plants, basic leucine zipper transcription factors (TFs) play important roles in multiple biological processes such as anthesis, fruit growth & development and stress responses. However, systematic investigation and characterization of bZIP-TFs remain unclear in Chinese white pear. Chinese white pear is a fruit crop that has important nutritional and medicinal values. RESULTS: In this study, 62 bZIP genes were comprehensively identified from Chinese Pear, and 54 genes were distributed among 17 chromosomes. Frequent whole-genome duplication (WGD) and dispersed duplication (DSD) were the major driving forces underlying the bZIP gene family in Chinese white pear. bZIP-TFs are classified into 13 subfamilies according to the phylogenetic tree. Subsequently, purifying selection plays an important role in the evolution process of PbbZIPs. Synteny analysis of bZIP genes revealed that 196 orthologous gene pairs were identified between Pyrus bretschneideri, Fragaria vesca, Prunus mume, and Prunus persica. Moreover, cis-elements that respond to various stresses and hormones were found on the promoter regions of PbbZIP, which were induced by stimuli. Gene structure (intron/exon) and different compositions of motifs revealed that functional divergence among subfamilies. Expression pattern of PbbZIP genes differential expressed under hormonal treatment abscisic acid, salicylic acid, and methyl jasmonate  in pear fruits by real-time qRT-PCR. CONCLUSIONS: Collectively, a systematic analysis of gene structure, motif composition, subcellular localization, synteny analysis, and calculation of synonymous (Ks) and non-synonymous (Ka) was performed in Chinese white pear. Sixty-two bZIP-TFs in Chinese pear were identified, and their expression profiles were comprehensively analyzed under ABA, SA, and MeJa hormones, which respond to multiple abiotic stresses and fruit growth and development. PbbZIP gene occurred through Whole-genome duplication and dispersed duplication events. These results provide a basic framework for further elucidating the biological function characterizations under multiple developmental stages and abiotic stress responses.

Transcriptome and metabolomic analysis to reveal the browning spot formation of 'Huangguan' pear.

BACKGROUND: Browning spot (BS) disorders seriously affect the appearance quality of 'Huangguan' pear and cause economic losses. Many studies on BS have mainly focused on physiological and biochemical aspects, and the molecular mechanism remains unclear. RESULTS: In the present study, the structural characteristics of 'Huangguan' pear with BS were observed via scanning electron microscopy (SEM), the water loss and brown spots were evaluated, and transcriptomic and metabolomics analyses were conducted to reveal the molecular mechanism underlying 'Huangguan' pear skin browning disorder. The results showed that the occurrence of BS was accompanied by a decrease in the wax layer and an increase in lignified cells. Genes related to wax biosynthesis were downregulated in BS, resulting in a decrease in the wax layer in BS. Genes related to lignin were upregulated at the transcriptional level, resulting in upregulation of metabolites related to phenylpropanoid biosynthesis. Expression of calcium-related genes were upregulated in BS. Cold-induced genes may represent the key genes that induce the formation of BS. In addition, the results demonstrated that exogenous NaH2PO4·2H2O and ABA treatment could inhibit the incidence of BS during harvest and storage time by increasing wax-related genes and calcium-related genes expression and increasing plant resistance, whereas the transcriptomics results indicated that GA3 may accelerate the incidence and index of BS. CONCLUSIONS: The results of this study indicate a molecular mechanism that could explain BS formation and elucidate the effects of different treatments on the incidence and molecular regulation of BS.

Packham's Triumph Pears (Pyrus communis L.) Post-Harvest Treatment during Cold Storage Based on Chitosan and Rue Essential Oil.

Pears (Pyrus communis L.) cv. Packham's Triumph are very traditional for human consumption, but pear is a highly perishable climacteric fruit with a short shelf-life affected by several diseases with a microbial origin. In this study, a protective effect on the quality properties of pears was evidenced after the surface application of chitosan-Ruta graveolens essential oil coatings (CS + RGEO) in four different concentrations (0, 0.5, 1.0 and 1.5 %, v/v) during 21 days of storage under 18 °C. After 21 days of treatment, a weight loss reduction of 10% (from 40.2 ± 5.3 to 20.3 ± 3.9) compared to the uncoated pears was evident with CS + RGEO 0.5%. All the fruits' physical-chemical properties evidenced a protective effect of the coatings. The maturity index increased for all the treatments. However, the pears with CS + RGEO 1.5% were lower (70.21) than the uncoated fruits (98.96). The loss of firmness for the uncoated samples was higher compared to the coated samples. The pears' most excellent mechanical resistance was obtained with CS + RGEO 0.5% after 21 days of storage, both for compression resistance (7.42 kPa) and force (22.7 N). Microbiological studies demonstrated the protective power of the coatings. Aerobic mesophilic bacteria and molds were significantly reduced (in 3 Log CFU/g compared to control) using 15 µL/mL of RGEO, without affecting consumer perception. The results presented in this study showed that CS + RGEO coatings are promising in the post-harvest treatment of pears.

Efficacy of postharvest sodium nitroprusside application to extend storability by regulating physico-chemical quality of pear fruit.

Quality loss in pear fruit during storage reduces its marketability for long run. To increase its storability, the efficacy of postharvest dip treatment donor sodium nitroprusside (SNP) 0.000, 0.001, 0.002 and 0.003 mol L-1 were investigated on pear fruit cv. Patharnakh under storage conditions (low temperature 0-1 °C and relative humidity (90-95%). SNP effectively lowered fruit mass loss, retained colour and higher firmness, suppressed browning and respiration rate and sustained soluble solids content, titratable acidity, total phenol content and ascorbic acid thus conserved the fruit quality for longer period. SNP treatments suppressed the activity of polyphenol oxidase and increased activity of superoxide dismutase enzyme. Additionally, the SNP treated fruit exhibited lesser activities of fruit softening enzymes like pectin methylesterase, polygalacturonase and cellulase. Among all, 0.002 mol L-1 SNP concentration was superior to lengthen storability and sensory quality of pear up to 60 d under cold storage.

Effect of 1-MCP and ethylene absorbent on the development of lenticel disorder of 'Xinli No.7' pear and possible mechanisms.

BACKGROUD: A common lenticel disorder which occurs in the peel of 'Xinli No. 7' pears (Pyrus bretschneideri Rehd.) had not previously been described. Symptoms of this lenticel disorder include enlarging and bulging of the lenticels which results in significant commercial losses. Understanding the physiological basis of lenticel disorder and developing practical methods to control it is crucial for the successful marketing of this pear. RESULTS: The development of this lenticel disorder was found to be closely related to the endogenous ethylene production during storage. 1-Methylcyclopropene (1-MCP) combined with an ethylene absorbent (EA) treatment was found to significantly reduce the development of the disorder by inhibiting the expression of ethylene related genes, PbACS1, PbACS2 and PbACO. It is proposed that the enlarged lenticels may result from increased lignin accumulation in the peel cells, which is inhibited by this combined postharvest treatment. It was shown that the expression of six lignin related genes decreased following the treatment. The results suggest that PbPAL, Pb4CL and PbCAD could be critical in regulating the development of this lenticel disorder. CONCLUSION: Endogenous ethylene plays a key role in the development of this lenticel disorder in 'Xinli No. 7' pear. The enlarged lenticels which is characteristic of this disorder maybe related to increased lignin accumulation in the peel cells, which were inhibited with 1-MCP combined with an EA treatment. These results provide a practical method for managing the development of lenticel disorder in 'Xinli No. 7' pear and helps clarify the developmental mechanisms of this disorder. © 2020 Society of Chemical Industry.

Browning and quality management of pear fruit by salicylic acid treatment during low temperature storage.

BACKGROUND: 'Patharnakh' pear, a dominant cultivar in the Punjab province of India, has a shorter storage life as it matures during the hot and humid weather. Studies have reported that postharvest chemical treatments have a major role in improving the storage life of the fruit. In this study, the efficacy of different concentrations (1, 2, and 3 mmol L-1 ) of salicylic acid (SA), a well-known signaling molecule, was explored to overcome browning and maintain the postharvest quality of the Patharnakh pear during cold storage. RESULTS: SA treated pears were better than the untreated fruits in all of the studied parameters. SA application alleviated the rate of weight loss and respiration, and lowered the decay percentage. The efficacy of SA in the reduction of polyphenol oxidase (PPO) activity, which correlates negatively with the total phenolic content, was quite noticeable. The SA treated fruits exhibited a slower oxidation of the total phenol content by inhibiting the action of PPO and retaining the total phenolic content, leading to lower incidence of browning. SA effectively maintained the ascorbic acid content and superoxide dismutase activity. Total soluble solids, titratable acidity, ascorbic acid, and pH of the pears were highest with the SA treatment. CONCLUSION: The 2 mmol L-1 SA treatment exhibited the best result of reducing fruit decay and tissue browning, and maintaining the postharvest quality parameters of pear up to 60 days of cold storage. © 2020 Society of Chemical Industry.

Methyl jasmonate pretreatment improves aroma quality of cold-stored 'Nanguo' pears by promoting ester biosynthesis.

Cold storage is widely used for delaying ripening and senescence; however, fruit aroma diminishes noticeably after long-term cold storage. The esters synthesized by the lipoxygenase (LOX) pathway are responsible for 'Nanguo' pear aroma. As methyl jasmonate (MeJA) is known to act on various fruit qualities, we investigated whether it acts via the LOX pathway in cold-stored 'Nanguo' pears. MeJA treatment increased the content of volatile esters and unsaturated fatty acids and the activities of alcohol acyltransferase, alcohol dehydrogenase, and LOX. It also up-regulated the expression of key genes (PuAAT, PuADH3, PuADH5, PuADH9, PuLOX1, and PuLOX3) in the LOX pathway and that of transcription factors (PuMYB21-like, PuMYB108-like, PuWRKY61, PuWRKY72, and PuWRKY31), whose genes were differentially expressed in preliminary transcriptome analysis. Therefore, considering its effects on LOX pathway-related genes and transcription factors, MeJA may be useful in preventing cold-storage-induced decline in ester biosynthesis, aroma, and consequently the quality of cold-stored 'Nanguo' pears.

Genome-wide characterization of the cellulose synthase gene superfamily in Pyrus bretschneideri and reveal its potential role in stone cell formation.

Members of the cellulose synthase (CesA) and cellulose synthase-like (Csl) families from the cellulose synthase gene superfamily participate in cellulose and hemicellulose synthesis in the plasma membrane. The members of this superfamily are vital for cell wall construction during plant growth and development. However, little is known about their function in pear fruit, a model for Rosaceae species and for fleshy fruit development. In our research, a total of 36 CesA/Csl family members were identified from the pear and were grouped into six subfamilies (CesA, CslB, CslC, CslD, CslE, and CslG) according to phylogenetic relationships. We performed a protein sequence physicochemical analysis, phylogenetic tree construction, a gene structure, a conserved domain, and chromosomal localization analysis. The results indicated that most of the CesA/Csl genes from pear are closely related to genes in Arabidopsis, but these families have unique characteristics in terms of their gene structure, chromosomal localization, phylogeny, and deduced protein sequences, suggesting that they have evolved through different processes. Tissue expression analysis results showed that most of the CesA/Csl genes were constitutively expressed at different levels in different organs. Furthermore, the expression levels of four genes (Pbr032894.2, Pbr016107.1, Pbr00518.1, and Pbr034218.1) tended to first increase and then decrease during fruit development, implying that these four genes may be involved in the development of stone cells of pear fruit. Our results may help elucidate the evolutionary history and functional differences of the CesA/Csl genes in pear and lay a foundation for further investigation of the CesA/Csl genes in pear and other Rosaceae species.

Preharvest application of prohydrojasmon affects color development, phenolic metabolism, and pigment-related gene expression in red pear (Pyrus ussuriensis).

BACKGROUND: Peel color is an economically relevant trait that influences the appearance and quality of red pear, whose red color is due to anthocyanin accumulation. Prohydrojasmon (PDJ), which has similar effects to endogenous jasmonates, was developed as a commercial bioregulator, particularly to improve fruits coloring. However, little information is available about the effect of PDJ on pears. This study investigated the effects of preharvest PDJ treatments on color development, phenolic compounds accumulation, and related gene expression in the red pear cultivar 'Nanhong'. The treatments were performed during the pre-color-change period by spraying 50 or 100 mg L-1 of PDJ on fruits. RESULTS: Preharvest PDJ treatments had a significant effect on color development, without affecting other quality parameters such as total soluble solids and fruit acidity. Liquid chromatography-mass spectrometry analysis showed that concentrations of anthocyanins and flavonols were enhanced in the peel after PDJ treatments, particularly when a concentration of 100 mg L-1 was used, whereas those of hydroxycinnamates and flavanols were decreased. After PDJ application, the transcription levels of anthocyanin biosynthesis genes PAL, CHS, CHI, ANS, F3H, and UFGT were enhanced, especially under the higher PDJ concentration tested. In addition, anthocyanin accumulation in the peels of PDJ-treated fruits was found to be positively correlated with the upregulation of the regulatory gene MYB114. CONCLUSION: Preharvest treatments with PDJ could be a useful tool to improve fruits coloring and increase phenolic content in pear. These findings also improve our understanding of the molecular mechanisms associated with PDJ-regulated anthocyanin accumulation in pear fruits.

Postharvest Application of Acibenzolar-S-methyl Delays the Senescence of Pear Fruit by Regulating Reactive Oxygen Species and Fatty Acid Metabolism.

This study investigated the changes in enzyme activity and gene expression in reactive oxygen species (ROS) and fatty acid metabolism in Docteur Jules Guyot pears after acibenzolar-S-methyl (ASM) treatment to elucidate the role of ROS and fatty acid metabolism in senescence. The results demonstrated that applying ASM postharvest significantly suppressed H2O2 content and enhanced catalase and superoxide dismutase activities in pears. Ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase activities and the reduced glutathione content in pears were also induced by ASM. Postharvest ASM dipping remarkably enhanced PcSOD, PcCAT, PcAPX, and PcDHAR expressions and fatty acid synthetase activity in pears. Postharvest applying ASM significantly decreased malondialdehyde content and lipoxygenase, hydroperoxidelyase, alcohol dehydrogenase, and alcohol acyltransferase activities in pears. ASM distinctly inhibited PcPLD, PcLOX, PcHPL, PcADH, and PcAAT expressions in pears. The findings suggest that postharvest applying ASM could modulate ROS and fatty acid metabolism to delay senescence in pears.

Acid vacuolar invertase 1 (PbrAc-Inv1) and invertase inhibitor 5 (PbrII5) were involved in sucrose hydrolysis during postharvest pear storage.

In pear, sucrose was mainly distributed in vacuole; and the alternation of sucrose abundance was associated the change of vacuolar invertase (VI) activity during fruit storage. However, the molecular mechanism beneath such phenomenon has not been clarified until recently. For this, a combination of metabolite, enzyme activity, transcriptome, quantitative real-time PCR (qRT-PCR), bioinformation, subcellular localization, and transient overexpression assay was conducted in this study to identify the acid invertase 1 (PbrAc-Inv1) and invertase inhibitor 5 (PbrII5) involved in sucrose degradation during 'Housui' pear storage. Both PbrAc-Inv1 and PbrII5 were located in vacuolar membrane. PbrAc-Inv1 could accelerate sucrose degradation; on the other hand, PbrII5 could bind with PbrAc-Inv1 to form a inactive complex, downregulate the VI activity, and suppressed sucrose decomposition. Based on Bio-layer interferometry (BLI) result after domain substitution, the domain on the left of catalytic 'WEC-P/V-D' box in PbrAc-Inv1 might played a key role in its interaction with PbrII5.

Glycine betaine treatment alleviates loss of aroma-related esters in cold-stored 'Nanguo' pears by regulating the lipoxygenase pathway.

Glycine betaine (GB) is known to alleviate chilling injury in many fruit species. Therefore, we studied how GB affects the biosynthesis of esters in 'Nanguo' pears. Based on the kinds of esters, total esters, and the quantity of the main esters, it was evident that aroma losses were alleviated by GB treatment. In addition, unsaturated fatty acids contents (linoleic and linolenic acid) and the activities of lipoxygenase (LOX) and alcohol acyltransferase (AAT) enzymes were also increased. Meanwhile, comparing with the control fruit, the genes directly involved in ester synthesis were up-regulated in the GB-treated fruit. In addition, an increase in the activities and gene expression of antioxidant enzymes was observed in the treated samples. Thus, GB treatment promotes the synthesis of esters by regulating the LOX pathway and increasing antioxidant capacity, thereby effectively improving the quality of esters in cold-stored fruit.

Exogenous glycine betaine treatment alleviates low temperature-induced pericarp browning of 'Nanguo' pears by regulating antioxidant enzymes and proline metabolism.

The effect of glycine betaine (GB) on chilling injury (CI)-induced pericarp browning in 'Nanguo' pears was investigated during shelf life at 20 °C after storage at 0 °C for 120 d. GB treatment alleviated the severity of browning in 'Nanguo' pears as represented by lower browning index (BI) and browning incidence. Membrane lipid peroxidation in GB-treated fruit was lower than that in the control, and membrane integrity was maintained in good condition. The activities and expression of ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD) were higher in GB-treated fruit than in control fruit. Furthermore, significantly higher proline content, proline synthesis key enzyme activities, and gene expression were observed in the treated fruit, including ornithine d-aminotransferase (OAT) and Δ1-pyrroline-5-carbox-ylate synthetase (P5CS), which were consistent with the browning tendency. In a nutshell, GB treatment can effectively alleviate pericarp browning of cold-stored 'Nanguo' pears by regulating antioxidant enzymes and proline metabolism.

Investigations into the production of volatile compounds in Korla fragrant pears (Pyrus sinkiangensis Yu).

The composition of volatile compounds in Korla fragrant pears was determined using headspace solid-phase microextraction followed by a gas chromatography-mass spectrometry analysis using fruits at 30, 90, and 150 days after bloom. Hexanal, (E)-2-hexenal, 1-hexanol, (E)-2-hexen-1-ol, (Z)-3-hexen-1-ol, and hexyl acetate were identified as the major compounds. The composition of volatile compounds was associated with fatty acid concentrations and key enzyme activity in the lipoxygenase pathway. In vitro linoleic and linolenic acid feeding experiments conducted using cubes of fruit flesh demonstrated that the concentrations of volatile esters, such as hexyl acetate, in the treated fruits increased significantly after incubation for 12 h compared with those in the control fruits, which was accompanied by a reduction in aldehyde and alcohol concentrations (p < 0.05 or p < 0.01). However, the treatments did not significantly influence the enzyme activity and expression of genes encoding the enzymes.

Effects of Melatonin Treatment of Postharvest Pear Fruit on Aromatic Volatile Biosynthesis.

Aroma affects the sensory quality of fruit and, consequently, consumer satisfaction. Melatonin (MT) is a plant growth regulator used to delay senescence in postharvest fruit during storage; however, its effect on aroma of pear fruit remains unclear. In this study, we assessed the effects of 0.1 mmol L-1 MT on volatiles and associated gene expression in the fruit of pear cultivars 'Korla' (Pyrus brestschneideri Rehd) and 'Abbé Fetel' (Pyrus communis L.). MT mainly affected the production of C6 aromatic substances in the two varieties. In 'Korla', MT inhibited expression of PbHPL, and reduced hydroperoxide lyase (HPL) activity and content of hexanal and (E)-hex-2-enal. In contrast, MT inhibited activity of lipoxygenase (LOX), reduced expression of PbLOX1 and PbLOX2, promoted PbAAT gene expression, increased alcohol acyltransferase (AAT) activity, and increased propyl acetate, and hexyl acetate content in 'Abbé Fetel' that similarly led to the reduction in content of hexanal and (E)-hex-2-enal. Content of esters in 'Abbé Fetel' pear increased with increasing postharvest storage period. Although mechanisms differed between the two varieties, effects on aroma volatiles mediated by MT were driven by expression of genes encoding LOX, HPL, and AAT enzymes.

Synthesis of indole-3-acetic acid and indole-3-butyric acid loaded zinc oxide nanoparticles: Effects on rhizogenesis.

The aim of this work was to investigate the use of zinc oxide nanoparticles (nZnO) as nanocarriers for plant auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) and determine the effects on rhizogenesis in micro cuttings of different Pyrus species. Auxin loaded nanoparticles (IAA-nZnO and IBA-nZnO) were characterized for particle size, morphology, thermal behavior and chemical structure. A high loading capacity was observed for both auxins (˜90%). Bioactivity assays were performed by using micro cuttings of Pyrus genotypes (Pyrus elaeagrifolia Pall and Pyrus communis L.) under aseptic conditions by dilute solution soaking method. In vitro rooting efficiency was increased at least two folds for the difficult-to-root wild pear (Pyrus elaeagrifolia Pallas) with IAA or IBA loaded ZnO nanoparticles. In this genotype, the highest rooting percentage was achieved for IBA-nZnO and IAA-nZnO at 400 mgL-1 concentration as 50.0% and 41.7%, respectively. Thus, auxin loaded ZnO nanoparticles could be used as efficient nanocarriers in agricultural applications.

Effects of melatonin treatment on the enzymatic browning and nutritional quality of fresh-cut pear fruit.

The effects of exogenous melatonin treatment on the enzymatic browning and nutritional quality of fresh-cut pear fruit were investigated. Fresh-cut fruit soaked with 0, 0.05, 0.1 and 0.5 mM melatonin were stored at 4 °C. Our results showed that 0.1 mM melatonin treatment was optimal for reducing the surface browning and maintaining the titratable acidity of the fresh-cut fruit, which significantly decreased MDA and H2O2 contents and the growth of microorganism, enhanced total phenolic content and antioxidant capacity, and delayed the reduction of ascorbic acid. Furthermore, melatonin treatment at 0.1 mM decreased the expression of genes involving in enzymatic browning pathway including POD, PPO1, PPO5 and LOX1, and reduced PPO activity. Moreover, this treatment increased the expression of PAL and CHS, and enhanced PAL and CHS activities. These results showed that melatonin treatment might be a promising strategy to alleviate browning and improve the nutritional quality of fresh-cut pear fruit.

In Silico Genome-Wide Analysis of Respiratory Burst Oxidase Homolog (RBOH) Family Genes in Five Fruit-Producing Trees, and Potential Functional Analysis on Lignification of Stone Cells in Chinese White Pear.

: The accumulation of lignin in fruit has a significant negative impact on the quality of fruit-producing trees, and in particular the lignin formation stimulates the development of stone cells in pear fruit. Reactive oxygen species (ROS) are essential for lignin polymerization. However, knowledge of the RBOH family, a key enzyme in ROS metabolism, remains unknown in most fruit trees. In this study, a total of 40 RBOHs were identified from five fruit-producing trees (Pyrusbretschneideri, Prunuspersica, Citrussinensis, Vitisvinifera, and Prunusmume), and 10 of these sequences came from Pyrusbretschneideri. Multiple sequence alignments revealed that all 10 PbRBOHs contained the NADPH_Ox domain and the six alpha-helical transmembrane domains (TM-I to TM-VI). Chromosome localization and interspecies phylogenetic tree analysis showed that 10 PbRBOHs irregularly distributed on 8 chromosomes and 3 PbRBOHs (PbRBOHA, PbRBOHB, and PbRBOHD) are closely related to known lignification-related RBOHs. Furthermore, hormone response pattern analysis showed that the transcription of PbRBOHs is regulated by SA, ABA and MeJA. Reverse transcription-quantitative real-time polymerase chain reaction (qRT-PCR) and transcriptome sequencing analysis showed that PbRBOHA, PbRBOHB, and PbRBOHD accumulated high transcript abundance in pear fruit, and the transcriptional trends of PbRBOHA and PbRBOHD was consistent with the change of stone cell content during fruit development. In addition, subcellular localization revealed that PbRBOHA and PbRBOHD are distributed on the plasma membrane. Combining the changes of apoplastic superoxide (O2.-) content and spatio-temporal expression analysis, these results indicate that PbRBOHA and PbRBOHD, which are candidate genes, may play an important role in ROS metabolism during the lignification of pear stone cells. This study not only provided insight into the molecular characteristics of the RBOH family in fruit-producing trees, but also lays the foundation for studying the role of ROS in plant lignification.

PbrSLAH3 is a nitrate-selective anion channel which is modulated by calcium-dependent protein kinase 32 in pear.

BACKGROUND: The functional characteristics of SLAC/SLAH family members isolated from Arabidopsis thaliana, poplar, barley and rice have been comprehensively investigated. However, there are no reports regarding SLAC/SLAH family genes from Rosaceae plants. RESULTS: In this study, the function of PbrSLAH3, which is predominately expressed in pear (Pyrus bretschneideri) root, was investigated. PbrSLAH3 can rescue the ammonium toxicity phenomenon of slah3 mutant plants under high-ammonium/low-nitrate conditions. In addition, yeast two-hybrid and bimolecular fluorescence complementation assays confirmed that PbrSLAH3 interacts with PbrCPK32. Moreover, when PbrSLAH3 was co-expressed with either the Arabidopsis calcium-dependent protein kinase (CPK) 21 or PbrCPK32 in Xenopus oocytes, yellow fluorescence was emitted from the oocytes and typical anion currents were recorded in the presence of extracellular NO3-. However, when PbrSLAH3 alone was injected, no yellow fluorescence or anion currents were recorded, suggesting that anion channel PbrSLAH3 activity was controlled through phosphorylation. Finally, electrophysiological and transgene results showed that PbrSLAH3 was more permeable to NO3- than Cl-. CONCLUSION: We suggest that PbrSLAH3 crossing-talk with PbrCPK32 probably participate in transporting of nitrate nutrition in pear root.