Effects of Potassium-Containing Fertilizers on Sugar and Organic Acid Metabolism in Grape Fruits.

To identify suitable potassium fertilizers for grape (Vitis vinifera L.) production and study their mechanism of action, the effects of four potassium-containing fertilizers (complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate) on sugar and organic acid metabolism in grape fruits were investigated. Potassium-containing fertilizers increased the activity of sugar and organic acid metabolism-related enzymes at all stages of grape fruit development. During the later stages of fruit development, potassium-containing fertilizers increased the total soluble solid content and the sugar content of the different sugar fractions and decreased the titratable acid content and organic acid content of the different organic acid fractions. At the ripening stage of grape fruit, compared with the control, complex fertilizer, potassium nitrate, potassium sulfate, and potassium dihydrogen phosphate increased the total soluble solid content by 1.5, 1.2, 3.5, and 3.4 percentage points, decreased the titratable acid content by 0.09, 0.06, 0.18, and 0.17 percentage points, respectively, and also increased the total potassium content in grape fruits to a certain degree. Transcriptome analysis of the differentially expressed genes (DEGs) in the berries showed that applying potassium-containing fertilizers enriched the genes in pathways involved in fruit quality, namely, carbon metabolism, carbon fixation in photosynthetic organisms, glycolysis and gluconeogenesis, and fructose and mannose metabolism. Potassium-containing fertilizers affected the expression levels of genes regulating sugar metabolism and potassium ion uptake and transport. Overall, potassium-containing fertilizers can promote sugar accumulation and reduce acid accumulation in grape fruits, and potassium sulfate and potassium dihydrogen phosphate had the best effects among the fertilizers tested.

Effects of L-Cysteine and γ-Aminobutyric Acid Treatment on Postharvest Quality and Antioxidant Activity of Loquat Fruit during Storage.

Sichuan is the China's leading producer of loquat, with the largest cultivation area and yield ranked first in China. Loquat is a seasonal fruit highly appreciated by consumers; however, the fruit is prone to browning and lignification after harvest, affecting its storage quality. The effects of L-Cysteine (L-Cys, 0.01, 0.05, 0.1, 0.2%) and γ-aminobutyric acid (GABA, 0.025, 0.05, 0.075, 0.1%) on the sensory quality and antioxidant activity of loquat fruit during cold storage at 4 °C for 35 days and simulated shelf life for 5 days were investigated. The results showed that after 40 days of storage, compared with the control, 0.05% L-Cys and 0.05% GABA treatment of 'Zaozhong No. 6' loquat fruit effectively reduced the weight loss rate, browning index, decay index, respiratory rate, firmness, and lignin content and slowed the decreases in total soluble solids, soluble sugar, titratable acidityand vitamin C contents. The application of 0.05% L-Cys and 0.05% GABA significantly increased the contents of total phenols, total flavonoids, flavanols, and carotenoids; delayed the increase of relative electric conductivity, MDA, POD, and PPO activities; and significantly enhanced the activities of SOD and CAT, DPPH free radical scavenging ability, and FRAP, thereby improving antioxidant capacity. In summary, 0.05% L-Cys and 0.05% GABA treatment promotes the quality of loquat fruit after 40 days of storage, and significantly enhances antioxidant capacity, thus delaying senescence after harvest.

Dynamic Changes of Phenolic Composition, Antioxidant Capacity, and Gene Expression in 'Snow White' Loquat (Eriobotrya japonica Lindl.) Fruit throughout Development and Ripening.

The newly released 'Snow White' (SW), a white-fleshed loquat (Eriobotrya japonica Lindl.) cultivar, holds promise for commercial production. However, the specifics of the phenolic composition in white-fleshed loquats, along with the antioxidant substances and their regulatory mechanisms, are not yet fully understood. In this study, we examined the dynamic changes in the phenolic compounds, enzyme activities, antioxidant capacity, and gene expression patterns of SW during the key stages of fruit development and ripening. A total of 18 phenolic compounds were identified in SW, with chlorogenic acid, neochlorogenic acid, and coniferyl alcohol being the most predominant. SW demonstrated a stronger antioxidant capacity in the early stages of development, largely due to total phenolics and flavonoids. Neochlorogenic acid may be the most significant antioxidant contributor in loquat. A decline in enzyme activities corresponded with fruit softening. Different genes within a multigene family played distinct roles in the synthesis of phenolics. C4H1, 4CL2, 4CL9, HCT, CCoAOMT5, F5H, COMT1, CAD6, and POD42 were implicated in the regulation of neochlorogenic acid synthesis and accumulation. Consequently, these findings enhance our understanding of phenolic metabolism and offer fresh perspectives on the development of germplasm resources for white-fleshed loquats.

Effects of intercropping with Solanum photeinocarpum and its post-grafting generations on cadmium accumulation in loquat (Eriobotrya japonica).

Cadmium (Cd) contamination of orchard soils is a global problem that has been increasing. To decrease the Cd accumulation in fruits, intercropping the orchard crops with hyperaccumulator plants has been used for soil remediation. A pot and a field experiment were conducted to study the effects of intercropping the potential Cd-hyperaccumulator Solanum photeinocarpum and its post-grafting generations with loquat (Eriobotrya japonica) on the growth and Cd uptake of these two plant species. In the pot experiment, intercropping improved the biomass, Cd content, Cd extraction, and root-to-shoot Cd translocation in both species. Intercropping increased the DNA methylation levels, antioxidant enzyme activity, and soluble protein content of loquat seedlings. These results indicate that intercropping could improve the phytoremediation of S. photeinocarpum and its post-grafting generations and increase the Cd uptake in loquat seedlings. In the field experiment, intercropping increased the Cd contents in the old branches, while it decreased that in the young branches and fruits of loquat. These findings indicate that intercropping could increase the Cd uptake in old tissues but reduce the Cd uptake in young tissues and fruits of loquat. So, intercropping loquat with S. photeinocarpum and its post-grafting generations could be used in Cd-contaminated orchards.

Intercropping the potential Cd-hyperaccumulator Solanum photeinocarpum and its post-grafting generations with loquat mutually promoted the growth of two plant species, and also promoted the cadmium uptakes in S. photeinocarpum and old branches of loquat, while inhibited the Cd uptake in the loquat young tissues (young branches and fruits). These results are the new findings of the intercropping.

Genome-Wide Identification of MYB Transcription Factors and Screening of Members Involved in Stress Response in Actinidia.

MYB transcription factors (TFs) play an active role in plant responses to abiotic stresses, but they have not been systematically studied in kiwifruit (Actinidia chinensis). In this study, 181 AcMYB TFs were identified from the kiwifruit genome, unevenly distributed on 29 chromosomes. The high proportion (97.53%) of segmental duplication events (Ka/Ks values less than 1) indicated that AcMYB TFs underwent strong purification selection during evolution. According to the conservative structure, 91 AcR2R3-MYB TFs could be divided into 34 subgroups. A combination of transcriptomic data under drought and high temperature from four AcMYB TFs (AcMYB2, AcMYB60, AcMYB61 and AcMYB102) was screened out in response to stress and involvement in the phenylpropanoid pathway. They were highly correlated with the expression of genes related to lignin biosynthesis. qRT-PCR analysis showed that they were highly correlated with the expression of genes related to lignin biosynthesis in different tissues or under stress, which was consistent with the results of lignin fluorescence detection. The above results laid a foundation for further clarifying the role of MYB in stress.

Melatonin improves heat tolerance in Actinidia deliciosa via carotenoid biosynthesis and heat shock proteins expression.

The whole-genome molecular mechanisms of melatonin (MT)-mediated enhancement of thermotolerance in plants has rarely been studied. In this study, the genome-wide gene expression profiles of kiwifruit seedlings primed with MT and non-MT at 45°C were analyzed by RNA-Seq. A total of 3299 differentially expressed genes (DEGs) were screened between MT and non-MT treatment, in which carotenoid biosynthesis was one of the high-enrichment pathways revealed by Kyoto Encyclopedia of Genes and Genomes analysis. Further, qRT-PCR verified that MT significantly induced the upregulated expression of the carotenoid biosynthesis gene, which was consistent with the increase of carotenoid content. In addition, 10 heat shock proteins (HSPs) were identified to have a highly upregulated expression by MT. These findings provide a set of informative and fundamental data on the role of MT in heat resistance.

Effects of exogenous methyl jasmonate on the synthesis of endogenous jasmonates and the regulation of photosynthesis in citrus.

Methyl jasmonate (MeJA) is an airborne signaling phytohormone that can induce changes in endogenous jasmonates (JAs) and cause photosynthetic responses. However, the response of these two aspects of citrus plants at different MeJA concentrations is still unclear. Four MeJA concentrations were used in two citrus varieties, Huangguogan (C. reticulata × C. sinensis) and Shiranuhi [C. reticulata × (C. reticulata × C. sinensis)], to investigate the effects of MeJA dose on the endogenous JAs pathway and photosynthetic capacity. We observed that MeJA acted in a dose-dependent manner, and its stimulation in citrus leaves showed a bidirectional character at different concentrations. This work demonstrates that MeJA at only a concentration of 2.2 mM or less contributed to the activation of magnesium protoporphyrin IX methyltransferase (ChlM, EC 2.1.1.11) and protochlorophyllide oxidoreductase (POR, EC 1.3.1.11) and the simultaneous accumulation of Chl a and Chl b, which in turn contributed to an improved photosynthetic capacity and PSII photochemistry efficiency of citrus. Meanwhile, the inhibition of endogenous JAs synthesis by exogenous MeJA was observed. This was achieved by reducing the ratio of monogalactosyl diacylglycerol (MGDG) to diagalactosyl diacylglycerol (DGDG) and inhibiting the activities of key enzymes in JAs synthesis, especially 12-oxo-phytodienoic acid reductase (OPR, EC 1.3.1.42). Another noteworthy finding is that there may exist a JA-independent pathway that could regulate 12-oxo-phytodienoic acid (OPDA) synthesis. This study jointly analyzed the internal hormone regulation mechanism and the external physiological response, as well as revealed the effects of exogenous MeJA on promoting the photosynthesis and inhibiting the endogenous JAs synthesis.

Effects of reciprocal grafting on cadmium accumulation in post-grafting generations of two ecotypes of Solanum photeinocarpum.

Farmland and mining ecotypes of the potential cadmium (Cd)-hyperaccumulator Solanum photeinocarpum were collected to study the effects of reciprocal grafting on the growth of, and Cd accumulation in, the post-grafting generations. The post generations of the following plant materials were evaluated in a pot experiment: the un-grafted farmland ecotype, grafted plants with the farmland ecotype as the scion or the rootstock, the un-grafted mining ecotype, and grafted plants with the mining ecotype as the scion or the rootstock. The results showed that reciprocal grafting increased the biomass, the activities of superoxide dismutase, peroxidase, and catalase, and the soluble protein content in the post-grafting generations of both ecotypes S. photeinocarpum. Reciprocal grafting also increased the Cd content in, and amount of Cd extracted by, the post-grafting generations of both ecotypes S. photeinocarpum as a result of lower soil pH and higher soil available Cd concentrations. Additionally, grafting affected the DNA methylation levels by inducing hypermethylation or demethylation in the post-grafting generation. Therefore, reciprocal grafting can enhance the Cd accumulation (phytoremediation) capacity of post-grafting generations of both ecotypes S. photeinocarpum by affecting DNA methylation levels.

Effects of different rootstocks on cadmium accumulation characteristics of the post-grafting generations of Galinsoga parviflora.

A pot experiment was conducted to study the effects of different rootstocks on the cadmium (Cd) accumulation characteristics of the post-grafting generations of Cd-hyperaccumulator Galinsoga parviflora plants. Five treatments, ungrafted and G. parviflora seedlings grafted on the rootstocks of Kalimeris indica, Senecio scandens, Conyza canadensis, and Artemisia sieversiana, were utilized. The four rootstock grafts decreased the shoot biomass of the G. parviflora post-grafting generation compared with ungrafted. The K. indica and S. scandens grafts increased the Cd concentration in shoots of the G. parviflora post-grafting generation by 15.06% and 14.40%, respectively, compared with ungrafted, while the C. canadensis and A. sieversiana grafts had no significant effects. K. indica grafts increased the amount of Cd extracted by shoots of the G. parviflora post-grafting generation by 10.59% compared with ungrafted, while the other treatments resulted in decreases. Compared with ungrafted, the different rootstocks had no significant effects on the photosynthetic pigment content of the G. parviflora post-grafting generation, and only C. canadensis grafts increased the superoxide dismutase activity level, while only K. indica grafts increased the peroxidase activity level. Therefore, the K. indica rootstock could increase the phytoremediation capability of G. parviflora post-grafted plants grown in Cd-contaminated soil.

Melatonin Accumulation in Sweet Cherry and Its Influence on Fruit Quality and Antioxidant Properties.

Although the effects of melatonin on plant abiotic and biotic stress resistance have been explored in recent decades, the accumulation of endogenous melatonin in plants and its influence on fruit quality remains unclear. In the present study, melatonin accumulation levels and the expression profiles of five synthesis genes were investigated during fruit and leaf development in sweet cherry (Prunus avium L.). Melatonin was strongly accumulated in young fruits and leaves, then decreased steadily with maturation. Transcript levels of PacTDC and PacSNAT were highly correlated with melatonin content in both fruit and leaves, indicating their importance in melatonin accumulation. Furthermore, application of 50 and 100 µmol·L-1 of melatonin to leaves had a greater influence on fruit quality than treatments applied to fruits, by significantly improving fruit weight, soluble solids content, and phenolic content including total phenols, flavanols, total anthocyanins, and ascorbic acid. Meanwhile, melatonin application promoted the antioxidant capacity of fruit assayed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylben zothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP). These results provide insights into the physiological and molecular mechanisms underlying melatonin metabolism of sweet cherry.

Effects of carboxymethyl chitosan on the growth and nutrient uptake in Prunus davidiana seedlings.

To determine the effects of carboxymethyl chitosan on plant growth and nutrient uptake, Prunus davidiana seedlings were treated with various concentrations of carboxymethyl chitosan. The biomass, physiological characteristics, and nutrient uptake of the treated P. davidiana seedlings were then examined. Compared with the control seedlings, the carboxymethyl chitosan-treated seedlings had a higher biomass and a greater abundance of photosynthetic pigments (i.e., chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), with the best concentration as 2 g/L carboxymethyl chitosan, which increased the shoot biomass and total chlorophyll content by 26.75% and 24.64%, respectively. Moreover, the application of carboxymethyl chitosan enhanced superoxide dismutase and catalase activities, increased the soluble protein content, and decreased the malondialdehyde and proline contents of the P. davidiana seedlings to some extent. Additionally, the carboxymethyl chitosan treatments decreased the total nitrogen content, but increased the total phosphorus and potassium contents in P. davidiana seedlings to some extent. The minimum of total nitrogen content and the maximum of total phosphorus and potassium contents in shoots of P. davidiana seedlings were the concentration of 2 g/L carboxymethyl chitosan, which was decreased by 12.96% and increased by 15.45% and 22.53%, respectively, compared with the control. Therefore, the application of a carboxymethyl chitosan solution may promote the growth, enhance the stress resistance, and alter the nutrient uptake of P. davidiana seedlings, especially at 2 g/L carboxymethyl chitosan.

Hydrogen cyanamide induces grape bud endodormancy release through carbohydrate metabolism and plant hormone signaling.

BACKGROUND: Grape buds exhibit non-uniform, or delayed, break in early spring in subtropical regions because the accumulation of chilling is insufficient. Hydrogen cyanamide (H2CN2, HC) can partially replace chilling to effectively promote bud sprouting and is used widely in warm winter areas. However, the exact underlying mechanism of grape bud release from endodormancy induced by HC remains elusive. RESULTS: In this study, the transcriptome of grape winter buds under in vitro conditions following HC and water treatment (control) was analyzed using RNA-seq technology. A total of 6772 differentially expressed genes (DEGs) were identified. Furthermore, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that starch and sucrose metabolism and plant hormone signaling transduction were most enriched out of the 50 total pathways. HC treatment induced the upregulated expression of sucrose synthase (SUS), sucrose phosphate synthase (SPS), α-amylase (AM), and ß-amylase (BM) and downregulated expression of sucrose invertase (INV), hexokinase (HK), fructokinase (FK), soluble starch synthase (SS), and granule-bound starch synthase (GBSS). Hence, the starch concentration in the HC-treated group was significantly lower than that in control, whereas soluble sugar content in the HC-treated group increased quickly and was higher than that in control between 0 and 8 d. The concentration of indoleacetic acid (IAA) and zeatin (ZT) increased, whereas that of abscisic acid (ABA) and gibberellin (GA) decreased in HC treated group, which coincided with the expression level of genes involved in above hormone signals. The content of hydrogen peroxide (H2O2) and enzyme activity of superoxide dismutase (SOD) and peroxidase (POD) were increased in grape buds with HC treatment, whereas catalase (CAT) activity was decreased. HC treatment increased the expression of POD, SOD, primary amine oxidase (PAO), polyamine oxidase (PAOX), and glutathione peroxidase (GSH-Px). CONCLUSION: Based on these results, it is possible to propose a mechanistic model that underlies the regulation of endodormancy release in grapevine buds by exogenous HC application.

Effects of intercropping with Bidens species plants on the growth and cadmium accumulation of Ziziphus acidojujuba seedlings.

To study the effects of intercropping with accumulator plants on heavy metal accumulation of fruit trees, plants of three Bidens species (Bidens pilosa, Bidens biternata, and Bidens parviflora) were intercropped with Ziziphus acidojujuba seedlings under cadmium (Cd)-contaminated conditions (5 mg kg-1). Intercropping with Bidens species increased the biomass and chlorophyll b content of Z. acidojujuba seedlings compared with monoculture, but decreased their carotenoid content. Intercropping with Bidens species also improved the activity of superoxide dismutase, peroxidase, and catalase in Z. acidojujuba seedlings compared with monoculture. Intercropping with Bidens species decreased the Cd content in the roots of Z. acidojujuba seedlings compared with monoculture. Conversely, when intercropped with B. pilosa, B. biternata, and B. parviflora, the Cd content in the shoots of Z. acidojujuba seedlings increased by 62.18%, 60.10%, and 62.18%, respectively, compared with that of those monocultured. When intercropped with Z. acidojujuba seedlings, the Cd accumulation amount of three Bidens species plants were ranked B. parviflora > B. biternata > B. pilosa. Therefore, intercropping with plants of three Bidens species is not suitable for Cd-contaminated jujube orchards.

Effects of living hyperaccumulator plants and their straws on the growth and cadmium accumulation of Cyphomandra betacea seedlings.

To determine whether the living hyperaccumulator plants and their straws have the same effects on the growth and heavy metal accumulation of common plants, two pot experiments (intercropping experiment and straw mulch experiment) were conducted to study the effects of living hyperaccumulator plants (Solanum photeinocarpum, Tagetes erecta, Galinsoga parviflora and Bidens pilosa) and their straws on the growth and cadmium (Cd) accumulation of common plant Cyphomandra betacea seedlings. Intercropping with T. erecta or B. pilosa promoted the growth of C. betacea seedlings compared with the monoculture, while intercropping with S. photeinocarpum or G. parviflora inhibited that. Intercropping with S. photeinocarpum decreased the Cd contents in the roots and shoots of C. betacea seedlings compared with the monoculture, but intercropping with the other plants did not. In the straw mulch experiment, the straw of S. photeinocarpum or T. erecta promoted the growth of C. betacea seedlings compared with the control, while the straw of G. parviflora or B. pilosa did not. The straw of S. photeinocarpum or T. erecta decreased the Cd contents in the shoots of C. betacea seedlings, and the straw of G. parviflora or B. pilosa increased the shoot Cd contents. Thus, intercropping with S. photeinocarpum and applying S. photeinocarpum or T. erecta straw can reduce the Cd uptake of C. betacea.

Melatonin Improves Heat Tolerance in Kiwifruit Seedlings through Promoting Antioxidant Enzymatic Activity and Glutathione S-Transferase Transcription.

Evidence exists to suggest that melatonin (MT) is important to abiotic stress tolerance in plants. Here, we investigated whether exogenous MT reduces heat damage on biological parameters and gene expression in kiwifruit (Actinidia deliciosa) seedlings. Pretreatment with MT alleviates heat-induced oxidative harm through reducing H2O2 content and increasing proline content. Moreover, MT application raised ascorbic acid (AsA) levels and the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We also observed elevation in the activity of enzymes related to the AsA-GSH cycle, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, MT application increased the expression of 28/31 glutathione S-transferase (GST) genes, reducing oxidative stress. These results clearly indicate that in kiwifruit, MT exerts a protective effect against heat-related damage through regulating antioxidant pathways.

Effects of indole-3-butytric acid on lead and zinc accumulations in Pseudostellaria maximowicziana.

Plant hormones can improve the phytoremediation capabilities of heavy metal hyperaccumulator plants. In this study, different doses of indole-3-butytric acid (IBA) were sprayed on the leaves of the lead (Pb) and zinc (Zn) accumulator plant Pseudostellaria maximowicziana, which was planted in Pb-Zn contaminated soil, and the effects of IBA on Pb and Zn accumulation levels in P. maximowicziana were studied. Spraying 25- and 50-mg/L IBA doses increased the stem, leaf and shoot biomasses of P. maximowicziana compared with the control, while 75- and 100-mg/L IBA doses decreased them. The 50-mg/L IBA dose increased the P. maximowicziana contents of chlorophyll a, total chlorophyll and carotenoid of compared with the control, and other doses had no significant effects or decreased these values. Spraying IBA reduced the superoxide dismutase activity of P. maximowicziana compared with the control, but improved the peroxidase and catalase activities. The 50-, 75-, and 100-mg/L IBA doses increased the Pb and Zn contents in P. maximowicziana compared with the control and also increased the amounts of Pb and Zn extracted by P. maximowicziana. Thus, 50 mg/L of IBA could promote the growth and the Pb and Zn phytoremediation capabilities of P. maximowicziana.

Transcriptome and biochemical analyses reveal phenolic compounds-mediated flavor differences in loquat (Eriobotrya japonica Lindl.) cultivars Chunhua No.1 and Dawuxing.

The novel loquat cultivar 'Chunhua No.1' (CH1) is a promising commercial cultivar. However, CH1 has texture characteristics different from those of common loquat, and its formation mechanism remains unclear. Here, we first identified the phenolic compounds of CH1 and its parent ('Dawuxing', DWX) and the effect on texture formation. The special presence of stone cells explained the flavor differences in CH1. Chlorogenic acid, neochlorogenic acid, and coniferyl alcohol were the main phenolic compounds in loquat, and the high content of coniferyl alcohol was a potential factor for the rough texture of CH1. Transcriptome reveals that phenylpropanoid metabolism was activated during CH1 fruit texture formation. Kyoto Encyclopedia of Genes and Genomes (KEGG) identified 51 structural genes involved in phenylpropanoid biosynthesis, and Weighted Gene Co-expression Network Analysis (WGCNA) identified four structural genes and 88 transcription factors. These findings provide new insights into the phenolic metabolism and flavor formation of loquat fruit.

Comparative Analysis of Carotenoid Profiles and Biosynthetic Gene Expressions among Ten Plum Cultivars.

Plums are good sources of various bioactive phytochemical compounds such as vitamins, anthocyanins, and carotenoids, whereby all of which are noted for multiple potential health benefits. However, knowledge regarding plum carotenoid profiles remains limited. Hence, the total and individual carotenoids in the edible parts (skin and flesh) of ten plum cultivars were determined using a spectrophotometer and high-performance liquid chromatography-diode array detection, respectively. Total and individual carotenoid contents in skin were significantly higher (p < 0.05) than those in flesh among all plum cultivars tested. The cultivars with the highest content of total carotenoids in skin were Naili (36.73 µg/g FW), followed by Yinhongli (21.81 µg/g FW) and Yuhuangli (19.70 µg/g FW), with the lowest in Angeleno (8.97 µg/g FW). Lutein, zeaxanthine, ß-cryptoxanthin, α-carotene, and ß-carotene were the major types of carotenoids detected, with lutein and ß-carotene being the predominant constituents of the skin and flesh tissues, respectively. Lutein, zeaxanthine, and total carotenoid contents were positively correlated with the expressions of PSY, LCYB, and LCYE, and negatively correlated with the expressions of PDS and CRTISO. Characterizing the carotenoid profiles and investigating variations in carotenoid biosynthetic gene expressions among plum cultivars are crucial for advancing genetic improvements in plums.

Genome-wide identification of the AcMADS-box family and functional validation of AcMADS32 involved in carotenoid biosynthesis in Actinidia.

MADS-box is a large transcription factor family in plants and plays a crucial role in various plant developmental processes; however, it has not been systematically analyzed in kiwifruit. In the present study, 74 AcMADS genes were identified in the Red5 kiwifruit genome, including 17 type-I and 57 type-II members according to the conserved domains. The AcMADS genes were randomly distributed across 25 chromosomes and were predicted to be mostly located in the nucleus. A total of 33 fragmental duplications were detected in the AcMADS genes, which might be the main force driving the family expansion. Many hormone-associated cis-acting elements were detected in the promoter region. Expression profile analysis showed that AcMADS members had tissue specificity and different responses to dark, low temperature, drought, and salt stress. Two genes in the AG group, AcMADS32 and AcMADS48, had high expression levels during fruit development, and the role of AcMADS32 was further verified by stable overexpression in kiwifruit seedlings. The content of α-carotene and the ratio of zeaxanthin/ß-carotene was increased in transgenic kiwifruit seedlings, and the expression level of AcBCH1/2 was significantly increased, suggesting that AcMADS32 plays an important role in regulating carotenoid accumulation. These results have enriched our understanding of the MADS-box gene family and laid a foundation for further research of the functions of its members during kiwifruit development.

Dynamic Changes in Cell Wall Polysaccharides during Fruit Development and Ripening of Two Contrasting Loquat Cultivars and Associated Molecular Mechanisms.

Loquats have drawn much attention due to their essential nutrients and unusual phenology, which fills a market gap in early spring. Fruit firmness (FF) is one of the most important quality attributes. Dynamic changes in FF, cell wall (CW) polysaccharides, CW hydrolase activity, and expression of CW metabolism-related genes during the fruit development and ripening stages of two contrasting loquat cultivars were compared. Although the two cultivars possessed similar FF at the initial fruitlet stage, Dawuxing was significantly firmer than Ninghaibai at all subsequent time points. FF was positively correlated with the contents of covalent-soluble pectin and hemicellulose, activity of peroxidase, and gene expressions of PME, EG, CAD6, and POD; and negatively correlated with the contents of water-soluble pectin, activities of polygalacturonase, endo-glucanase, cellobiohydrolase, and xylanase, and gene expressions of PG, EG2, PAL1, PAL3, and CAD5. Identifying molecular mechanisms underlying the differences in FF is useful for fundamental research and crop improvement in future.