Arbuscular mycorrhizal (AM) symbioses in plants are broadly significant because of their capacity to facilitate water and nutrient acquisition and thus, to promote vigorous growth and development among host plants. Many horticultural plants, especially citrus plants, are highly dependent on AM fungi. In return, AM fungi receive sugars and lipids from their host plants. The sugars (mainly sucrose) are transported from the aerial parts of host plants to the roots and thus, form a mycorrhizal carbon pool. In roots, sucrose is converted to hexoses, which are then taken up by AM fungal intraradical hyphae and converted to trehalose and glycogen for growth and storage in extraradical hyphae and potentially participate in the soil carbon cycle through as the glomalin-related soil proteins. Therefore, the root mycorrhizal carbon pool influences the sugar (mainly sucrose) metabolism of plants, providing a guarantee for mycorrhizal plants to maintain better plant growth, stress resistance, fruit quality, lateral root development, and soil carbon sequestration. Thus, sugar metabolism is a player in the dialog between AM fungi and plants. This review briefly summarizes the processes of sucrose synthesis, transport, and metabolism, and highlights the relationship between AM fungi and plant sugars with an emphasis on AM-carbon pools, osmotic adjustment, fruit quality, and sugar-associated gene expression. Future research prospects are discussed.
Frost in late spring is one form of environmental stress that severely damages grapevines. Starch is a major product of photosynthesis that plays essential roles in many biological processes in plants. The dynamics of starch metabolism and related gene expression in the leaves of grapevine during chilling stress have remained unclear. Here, starch metabolism in the leaves of Vitis vinifera cv. Cabernet Sauvignon was characterized under normal (25℃) and late-spring frost mimic (4℃) conditions. The results from anthracenone colorimetry, iodine staining and ultrathin sectioning are consistent with a low temperature during the night inhibiting the degradation of starch. Four α-amylases (AMY) and ten β-amylases (BAM) genes were identified in the V. vinifera genome (PN40024). Low nighttime temperatures downregulated the expression of genes that encode amylases relative to optimal nighttime temperatures. The expression of other genes with functions related to starch degradation, such as like starch excess four 1 (LSF1) and isoamylase 3 (ISA3), was induced by low temperature. The glucose, sucrose, maltose, and fructose contents increased in plants grown under low-temperature conditions with less consumption of starch, indicating complex regulation of soluble sugars. The findings here provide clues that will lead to enhanced frost tolerance of grapevine leaves by modifying the starch degradation pathway.
Citrus plants routinely experience a broad range of biotic and abiotic stress that occur either concurrently or sequentially in the field, causing huge losses in yield. Hence, cultivated citrus plants that tolerate only one type of abiotic stress are insufficient to maintain citrus productivity as the climate changes. Plants primarily develop delicate regulatory mechanisms to detect, transduce and respond to adverse environmental conditions. Therefore, elucidating the physiological, biochemical and molecular mechanisms underlying the dynamic response to multiple abiotic stresses is a prerequisite for determining the targets for genetic improvement programs of citrus. In this review, we pinpoint the current understanding of the physiological basis of citrus tolerance to abiotic stress. Then, we discuss recent insights into the integrated molecular mechanisms that are involved in the citrus response to multiple types of abiotic stress. Finally, we discuss recent prospects for using modern molecular technologies to facilitate the genetic improvement of citrus.
Citrus fruit coloration is one of the vital quality traits that is determined primarily by the composition and content of carotenoids. Natural citrus fruit pigment mutants are available to study diverse and complex carotenoid metabolism. Here, ‘Jinlegan’ (MT) tangor is a spontaneous bud mutant derived from ‘Shiranuhi’ (WT) with distinctive bright yellow fruit. High performance liquid chromatography (HPLC) analysis revealed that the yellowish MT flavedo and pulp were primarily caused by the decrease in total carotenoid content. The total carotenoid content in MT flavedo was reduced by 75% (79.98 μg/g DW) compared with that in WT (318.40 μg/g DW), including approximately 84%, 80%, and 60% reductions in the contents of β-cryptoxanthin, violaxanthin and zeaxanthin, respectively. The total carotenoid content in MT pulp was 60% lower (10.09 μg/g DW) than that in WT pulp (26.61 μg/g DW), which was mainly due to a 70% and 30% decrease in the contents of β-cryptoxanthin and zeaxanthin, respectively. To explore the molecular mechanism underlying carotenoid variation in MT, RNA-seq analyses were performed on the flavedo and pulp of WT and MT at five developmental stages. The reduced expression of phytoene synthase (Cr PSY) and β-carotene hydroxylase 1 (Cr BCH1) in the flavedo and pulp of MT at the breaker stage might be the major cause of the reduction in carotenoids. Weighted gene co-expression network analysis (WGCNA) further identified 23 key transcription factors that are closely associated with carotenoid accumulation. This study demonstrated a comprehensive picture of the metabolic and transcriptional alterations of a unique yellowish citrus fruit mutant, which provides new insights into the molecular regulation of carotenoid accumulation in citrus fruit.
Jasmonic acid (JA) is an important and widely distributed plant hormone. However, the molecular and physiological mechanism of JA in improving drought tolerance in response to sodium selenite is limited. This work was performed to investigate the effects of exogenous sodium selenite application in promoting drought tolerance of cucumber. The drought tolerance of cucumber seedlings is enhanced under the application of selenite, positively influencing shoot fresh weight and chlorophyll relative content and altering the chloroplast ultrastructure. The contents of JA and JA-isoleucine (JA-ILE) increased significantly in response to selenite application under drought conditions. Furthermore, the expression of JA biosynthesis and regulatory genes, namely, LOX (Lipoxygenase), AOC (allene oxide cyclase), AOS (allene oxide synthase), and MYC2 (the basic helix-loop-helix (bHLH) protein) was upregulated to greater levels when selenite was added in combination with drought treatment. This study provides methods to mitigate drought stress and valuable theoretical support for further understanding the plant response to drought signals.
Centromeres play a crucial role in ensuring the accurate separation of chromosomes during cell division. Despite the three rounds of genome sequencing technology undergone by Citrus sinensis (sweet orange), the presence of numerous repetitive DNA elements in its genome has led to substantial gaps in centromeric genomic mapping, leaving the composition of centromeric repeats unclear. To address this, we employed a combination of chromatin immunoprecipitation sequencing with the C. sinensis centromere-specific histone H3 variant antibody and centromere-specific bacterial artificial chromosome-3a sequencing to precisely locate the centromeres. This approach allowed us to identify a series of centromere-specific repeats, comprising five tandem repeats and nine long terminal repeat retrotransposons. Through comprehensive bioinformatics analysis, we gained valuable insights into potential centromeric evolution events and discovered the presence of DNA G-quadruplex structures of centromeric repeats in C. sinensis. Altogether, our study not only offers a valuable reference for centromeric genome assembly but also sheds light on the structural characteristics of C. sinensis centromeres.
Red leaves in autumn are characteristic of a very early-maturing ripening variety of peach (Prunus persica). Analysis of the genetic factors and molecular mechanisms associated with the red-leaf phenotype can help breed peach very early maturing peach varieties. This study investigated the mechanisms underlying the red- and green-leaf phenotypes in autumn. Red compounds accumulated in the older but not younger leaves in the extremely early-maturing peach variety, ‘99-30-33’, and the leaves of the medium-maturing variety, ‘Zhongtao5 (CP5)’. Metabolic analysis showed that cyanidin-3-O-glucoside was the most abundant anthocyanin in the red leaves. The segregation of the progenies obtained from crossing revealed that the red leaves are a unique hereditary phenomenon not in line with Mendel’s law. BSA-seq and RNA-seq analyses suggest that PpNAC1 was essential for enhancing anthocyanin biosynthesis and was highly upregulated in red than in green leaves. Similar to PpNAC1, the anthocyanin activator, PpMYB10.1, was the only gene highly expressed in red leaves. Moreover, the functional genes involved in anthocyanin biosynthesis, such as Prunus persica Flavonoid 3'-hydroxylase (PpF3'H), Prunus persicaDihydroflavonol reductase (PpDFR), Prunus persica Leucoantho-cyanidin dioxygenase (Pp LDOX), Prunus persica Glutathione S-transferase (PpGST), and Prunus persica UDP-glucose, flavonoid-3-O-glucosyltransferase (PpUFGT), were upregulated in the older red leaves of 99-30-33 but downregulated in the younger 99-30-33 and green CP5 leaves. Yeast one-hybrid and dual-luciferase assays further confirmed that PpNAC1, which refers to 'Prunus persica NAC (NAM、A TAF1/2、CUC1/2)' bound to the promoter of PpMYB10.1, PpMYB10.1 stands for 'Prunus persica MYB (v-myb avian myeloblastosis viral) 10.1' and activated its expression along with those of PpGST and PpUFGT. These results provide insights into the mechanisms responsible for the development of red color in peach leaves in autumn.
Grape production in China is significantly impacted by white rot disease, which is caused by Coniella diplodiella (Speg.) Sacc. This study analyzes the differences in leaf transcriptomes and phenotypes of two grape species, ‘Manicure Finger (Vitis vinifera L.)’ and ‘0940 (Vitis davidii Foex)’, following inoculation with C. diplodiella. Leaf anatomy and H2O2 content confirm the greater resistance of '0940' to C. diplodiella compared to 'Manicure Finger.' Comparative transcriptome analysis reveals that the defense mechanism of '0940' against C. diplodiella involves sesquiterpenoid and triterpenoid biosynthesis, plant-pathogen interactions, sulfur relay systems, suberin and wax biosynthesis, monoterpenoid biosynthesis, as well as flavonoid and flavonol biosynthesis pathways. Using Weighted Gene Co-expression Network Analysis (WGCNA), we identified three modules highly correlated with C. diplodiella resistance and 125 candidate genes, including resistant genes (R genes), pattern-recognition receptors (PRRs), and pathogenesis-related proteins genes (PR genes), which may play important roles in grape resistance to this disease.
Fruit ripening (FR) is attributed to the selective expression of several genes precisely governed by various specific transcription factors (TFs). The NAC (NAM, ATAF, and CUC) TF, MaNAC029, positively regulated banana ripening by directly inducing ethylene biosynthesis and transcription of fruit quality-related genes. However, its upstream regulatory mechanism still needs to be clarified. Herein, yeast one-hybrid screening revealed that a SQUAMOSA promoter binding protein-like (SPL) TF, MaSPL16, was a potentially upstream regulator of Musa acuminata N A C (NAM, ATAF, CUC) 0 2 9 (MaNAC029). Furthermore, gel mobility shift assay revealed that MaSPL16 can directly bound with the “GTAC” element of the MaNAC029 promoter. The gene expression and promoter activity assays demonstrated that Musa acuminata SPL (SQUAMOSA promoter binding protein-like) 16 (MaSPL16) expression was inducible by ethylene and ripening. MaSPL16 was localized to the nucleus, displayed a potenial capacity for transcriptional activation of MaNAC029. More critically, the transient expression of MaSPL16 in bananas accelerated FR via the upregulation of MaNAC029 and its downstream genes. Collectively, the mechanistic basis of a regulatory cascade involving MaSPL16-MaNAC029 that governed ethylene biosynthesis and fruit quality throughout the entire process of banana fruit ripening was unveiled. These outcomes increase the understanding of the gene-transcriptional regulatory mechanisms in FR. They are envisaged to help devise molecular techniques to regulate maturation and improve future fruit quality.
Fruit color influences fruit quality and commodity value. Most longan (Dimocarpus longan Lour.) varieties have a yellowish-brown or grayish-yellow pericarp, and the discovery of red pericarp (RP) longan expanded the color varieties of longan fruit. Our previous research showed that the red pericarp of RP fruit was mainly caused by anthocyanin accumulation; however, its underlying regulatory mechanism remains unknown. Herein, DlMYB113, an R2R3-MYB transcription factor, was discovered by examining differentially expressed genes in two longan cultivars. Dimocarpus longan MYB (v-myb avian myeloblastosis viral) 113 (DlMYB113) expression was significantly higher in the pericarp and leaves of RP longan than in ‘Shixia’ longan. Sequence alignment analysis revealed two amino acid substitutions in the R3 domain between DlMYB113rp in RP longan and DlMYB113sx in ‘Shixia’ longan. Transient expression of DlMYB113rp significantly increased anthocyanin accumulation in tobacco leaves, whereas DlMYB113sx had negligible effect. Meanwhile, DlMYB113 overexpression promotes anthocyanin accumulation in Arabidopsis and longan calli. Site-directed mutation detection revealed divergence in DlMYB113 function when the R3 repeat 197-position base T was replaced with G, and the 317- and 318-position AT bases were replaced with GA. Our findings indicate that DlMYB113 can regulate anthocyanin production in RP longan, and three mutations in its nucleic acid sequence lead to anthocyanin accumulation, thereby developing molecular markers associated with the anthocyanin accumulation trait in RP longan. This study will facilitate early screening of longan hybrids with desirable fruit color and be significant for breeding new characteristic varieties.
Pear (Pyrus bretschneideri), a valuable widely cultivated fruit, faces significant economic losses due to black spot disease caused by Alternaria alternate (Fr.) Keissl. Trihelix transcription factors (TFs) are crucial in regulating plant defense and autoimmunity. This study aimed to analyze the trihelix transcription factor (GT) genes within pear through genome-wide identification, phylogenetic, gene structure, synteny, and cis-acting elements analyses. Among the 31 trihelix genes, 28 were on 12 known chromosomes, while the remaining 3 were located on unknown chromosomes. These genes were categorized into five clades: SIP1, GTγ, GT1, GT2 and SH4, containing 7, 2, 9, 11 and 2 genes, respectively. Synteny analysis indicated eight duplicated gene pairs. Based on the expression pattern of PbGT genes in seven tissues from the database, the PbGT genes of the GT2 clade were selected for further investigation. The quantitative reverse transcriptase–polymerase chain reaction confirmed that PbrGT5, PbrGT6, PbrGT15 and PbrGT16 correlated with black spot disease resistance. Notably, the salicylic acid (SA) treatment significantly upregulated the expression levels of PbrGT10, PbrGT13, PbrGT15 and PbrGT23. Among these, PbrGT15 showed the highest induction to both SA and black spot infection. Subcellular localization demonstrated that PbrGT15 functions as a nuclear protein. Virus-induced gene silencing of PbrGT15 increased pear plants' susceptibility to black spot disease, indicating its pivotal role in enhancing resistance. These results indicated that PbrGT15 positively regulated black spot disease resistance in pears.
Conventional breeding in pears is inefficient due to a long juvenile phase and self-incompatibility. Genetic transformation offers a promise to expedite the breeding process. However, the frequencies of regeneration and genetic transformation in most Pyrus spp. are relatively low. This study investigated various factors influencing regeneration and genetic transformation using leaves from Pyrus ussuriensis Maxim “Shanli” and P. communis L. “Conference” as explants. The optimum regeneration medium for “Shanli” and “Conference” was NN69 containing 3.0 mg L−1 thidiazuron (TDZ) and 0.3 mg L−1 indolybutyric acid (IBA) for the former or 1.0 mg L−1 TDZ and 0.5 mg L−1 naphthalene acetic acid (NAA) for the latter. Sectioning the leaves from 30-day-old plantlets transversely and placing them with their abaxial side facing downward could significantly improve the regeneration ratio in both accessions. Moreover, a two- or four-week culture under the dark was beneficial for the regeneration of “Shanli” and “Conference” respectively. The optimal infection time was 12 and 8 min, while the time of the delayed screening test was two and one day for “Shanli” and “Conference” respectively. Moreover, a coculture of two days was recommended for both accessions. Post-transformation, the optimal concentrations of antibiotics were 16 mg L−1 kanamycin (Kan), 150 mg L−1 timentin (Tim), and 300 mg L−1 cefotaxime (Cef). The optimized regeneration and transformation system can be an effective alternative for either gene function analysis or genetic improvement in pear.
Abiotic stresses are major factors constraining the growth, development and productivity of tomato (Solanum lycopersicum), the most cultivated vegetable crop worldwide. Uridine diphosphate glycosyltransferases (UDPGTs or UGTs) are essential enzymes that utilize 5-uridine diphosphate as a glycosyl donor molecule to facilitate the catalysis of glycosylation reactions across diverse substrates, thereby playing a pivotal role in conferring abiotic stress tolerance. Currently, there is a limited understanding of the structure and functions of the UDPGT gene family in tomato. In this work, 106 members of the SlUDPGT gene family were identified through in silico analysis, besides, their protein sequence properties, phylogenetic relationships, gene structure, chromosomal distribution, cis-acting elements, tissue expression and hormone- and stress-induced expression were comprehensively investigated. The expression of representative SlUDPGTs under abiotic stress and exogenous hormone treatments, including salt, polyethylene glycol, methyl viologen, gibberellic acid, jasmonic acid, abscisic acid and brassinolide, was investigated through qRT‒PCR analysis. Numerous cis-acting elements linked to stress and hormone signaling were present in the promoter regions of SlUDPGTs. According to microarray data, most SlUDPGT genes were responsive to hormones and abiotic stresses, while certain SlUDPGTs were specifically differentially expressed under Botrytis cinerea and tomato spotted wilt virus infection. Additionally, diverse expression profiles of SlUDPGTs were observed in various tissues and developmental stages. Furthermore, CRISPR/Cas9-mediated knockout of SlUDPGT52 led to enhanced drought tolerance due to enhanced reactive oxygen species (ROS) scavenging. These findings lay the foundations for the future functional characterization of specific UDPGT gene family members, assisting the biotechnology-mediated improvement of tomato and other horticultural crops.
Snapdragon (Antirrhinum majus L.) is a widely cultivated and economically important cut flower and bedding plant worldwide due to its high ornamental value. At the same time, owing to its herbaceous features, ease of growth and cultivation, short life cycle, diploid inheritance, diverse morphological variation, and self-incompatibility, it has also been used as a model plant for studies on molecular biology, biochemistry, and plant developmental genetics. Over the past few decades, hundreds of plant genetics and physiology studies have been published on snapdragon. This review aims to summarize the advances in the characterization of snapdragon ornamental characters associated with floral organ size, shape, scent, color, and plant appearance. A broad spectrum of genes and their action mechanisms were explored and discussed, including comprehensive investigations at the genome-wide level and unraveling the functions of structural genes and master regulators and their interactions. In addition, the biosynthetic pathway involved in floral volatile scent production was summarized. Finally, the TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTORS (TCP) family in snapdragon was investigated using the latest whole-genome data. This review will lay the foundation for future molecular genetics and genomics research and applications on snapdragon. It further contributes to improve our knowledge of the mechanisms regulating morphogenesis and ornamental qualities in snapdragon.
WRKY transcription factors are pivotal regulators in various aspects of plant biology, including growth, development, secondary metabolic biosynthesis, and responses to both biotic and abiotic stresses. The legume plant Grona styracifolia is widely utilized for its medicinal properties in treating urinary calculi and combating SARS-CoV-2, owing to its bioactive component schaftoside. However, the regulatory function of GsWRKYs in schaftoside biosynthesis within G. styracifolia remains elusive. In the G. styracifolia genome, we identified a total of 102 GsWRKYs, classified phylogenetically into Group I (18), II (68), and III (16). Genomic analysis revealed an uneven distribution of GsWRKYs on chromosomes (Chr), with prevalence on Chr 1, followed by Chr 2, 3, 5, and 6. Among the 82 duplicated GsWRKYs, comprising 12, 54, and 16 members in Group I, II, and III respectively, 11 GsWRKYs were tandemly duplicated genes located across Chr 2 (2), Chr 5 (7), and Chr 9 (2). Weighted gene co-expression network analysis unveiled that 2 Group I (GsWRKY44 and GsWRKY95) and 14 Group II GsWRKYs, including two pairs of segmentally duplicated Group II GsWRKYs associated with thermomorphogenesis, exhibited coexpression with Grona styracifolia C-glycosyltransferases (GsCGT), a gene encoding a C-glucosyltransferase involved in schaftoside biosynthesis. Furthermore, GsWRKY95 demonstrated coexpression with other schaftoside biosynthetic genes. Dual-luciferase and yeast one-hybrid assays provided additional evidence that GsWRKY95 binds to the W-box of GsCGT, activating its expression. In addition, GsWRKY95- and GsCGT-coexpressing G r o na styracifolia chalcone synthase (GsCHSs), along with 11 pairs of segmentally duplicated Group II GsWRKYs, responded to both abiotic and biotic stresses. Notably, certain GsWRKYs were identified as regulators specific to schaftoside biosynthesis in stems, roots, and leaves. These findings suggest that duplication events, particularly in segmentally duplicated Group II GsWRKYs, play a pivotal role in orchestrating the hierarchical regulation of schaftoside biosynthesis. Overall, our results establish a foundation for genetically enhancing G. styracifolia to abundantly produce schaftoside, thereby contributing to its medicinal efficacy.
Petal senescence refers to the progressive loss of intracellular structures and functions within plant decorative organs, ultimately leading to cell death. Autophagy involves the degradation of damaged cellular components and nutrient recycling. Plant organ senescence and autophagy are highly coordinated; however, the mechanisms by which autophagy regulates petal senescence remain largely unknown. In this study, by using transmission electron microscopy, we observed that autophagic activity peaked early, at flower opening, without any senescence and other morphological symptoms in petals. We found that darkness positively regulated petal senescence and upregulated autophagy-related genes (ATGs). Dark treatment promoted the accumulation of Rosa hybrida phytochrome-interacting factor 4 (RhPIF4) in petals. RhPIF4 silencing delayed petal senescence and repressed the expression of ATGs. In contrast, silencing of the light-responsive gene Rosa hybrida elongated hypoctyl 5 (RhHY5) promoted petal senescence and ATG gene expression. RhPIF4/8 and RhHY5 could directly interact with RhWRKY40, and RhWRKY40 is directly bound to the promoters of RhATG7 and RhATG11. Silencing RhWRKY40 delayed petal senescence and suppressed RhATG7 and RhATG11 expression. Based on these results, we propose that RhPIF4/8 and RhHY5 transcription factors are involved in regulating petal senescence in response to dark or light conditions by modulating autophagic activity.
Adventitious root (AR) formation is critical for cutting survival and nutrient absorption re-establishment. This complex genetic trait involves the interplay of nitrogen, endogenous hormones, and several key genes. In this study, we treated GL-3 apple (Malus domestica) in vitro shoots with nitrate and ammonium to determine their impact on AR formation, hormonal content, and gene expression patterns. Nitrate treatment significantly promotes adventitious rooting by increasing cell division, differentiation, and AR primordia formation compared to ammonium treatment. Elevated indole-3-acetic acid (IAA), reduced abscisic acid, and zeatin riboside concentrations were consistently observed with nitrate, likely crucial for promoting ARs over ammonium. Furthermore, Malus domestica auxin resistance1 (MdAUX1) expression was induced, increasing IAA levels. MdIAA23 was upregulated. Further results indicate that the higher expression levels of Malus domestica WUSCHEL-related Homeobox gene 11 (MdWOX11), Malus domestica lateral organ boundaries domain gene 16 (MdLBD16), and MdLBD29, and increased cell cycle-related gene expressions, contribute to auxin-stimulated adventitious rooting under nitrate conditions. In conclusion, this study establishes that auxin content and associated genes related to root development and cell cycle contribute to superior ARs in response to nitrate.