Soil moisture plays a crucial regulatory role in determining the size and quality of citrus fruits. This study analyzed the fruit size and quality of citrus under different soil moisture conditions, including severe drought (SD), moderate drought (MD), and control (CK). Under drought stress, the fruit weight, longitudinal diameter, and transverse diameter of citrus fruits were significantly lower than those of the control. The content of soluble solids and titratable acid in fruits under drought stress was significantly higher than that of the control. Transcriptome sequencing revealed that compared with CK, there were 1186 differentially expressed genes in MD, including 414 up-regulated genes and 772 down-regulated genes; and 2315 differentially expressed genes in SD, including 1143 up-regulated genes and 1172 down-regulated genes. The differentially expressed genes were significantly enriched in cellular processes, metabolic processes, and plant hormone signal transduction. The down-regulated expression of auxin and gibberellin biosynthesis genes (YUC10, GA20OX1, GA2OX1, and GA20OX2) and signal transduction-related genes (AUX/IAA13, SAUR32, GH3.1, and ARRs), and the up-regulated expression of cytokinin decomposition gene (CKX5) may be associated with reduced fruit size under drought conditions. The up-regulated expression of citric acid synthesis genes (PEPC2 and PEPCK1) and vacuolar transporters (PH1, PH4, PH8, and VHA-c3) may be associated with pronounced accumulation of citric acid in citrus under drought stress. In conclusion, water control regulated fruit size and acidity by modulating phytohormone metabolism and signaling, along with the synthesis and transport of citric acid.

Salt stress is a major abiotic stress that threatens citrus yield and quality. To elucidate the molecular mechanisms underlying differential salt tolerance in citrus rootstocks, we performed an integrative transcriptomic and metabolomic analysis of salt-sensitive trifoliate orange (Poncirus trifoliata) and salt-tolerant Goutoucheng (Citrus aurantium) under 60 mM NaCl treatment for 12 h and 24 h. Physiological observations confirmed that Goutoucheng exhibited less growth inhibition and leaf damage than trifoliate orange. Transcriptome sequencing identified 2081 and 1588 differentially expressed genes (DEGs) in trifoliate orange at 12 h and 24 h, respectively, compared with 1166 and 997 DEGs in Goutoucheng. Metabolome profiling revealed 217 and 173 differentially accumulated metabolites (DAMs) in trifoliate orange versus 162 and 239 DAMs in Goutoucheng at the two time points. KEGG pathway analysis showed that DEGs were mainly enriched in the Mitogen-activated protein kinase (MAPK) signaling pathway—plant, plant hormone signal transduction, and flavonoid biosynthesis—and DAMs were mainly enriched in flavonoid biosynthesis, starch and sucrose metabolism, and glutathione metabolism. Integrative nine-quadrant and two-way orthogonal partial least squares analyses further pinpointed flavonoid biosynthesis as a central hub in salt response. Notably, quercetin derivatives accumulated preferentially in the salt-tolerant rootstock Goutoucheng. Several transcription factor families—including HSF, MYB, NAC, HB-HD-ZIP, C2H2, bHLH, AP2/ERF, and Trihelix—may enhance antioxidant capacity under salt stress by regulating flavonoid accumulation. Collectively, these results indicated that coordinated regulation of flavonoids contributed critically to salt stress adaptation in citrus rootstocks. The identified DEGs, DAMs, and transcription factors provide candidate targets for genetic improvement of salt tolerance in citrus.

Trifoliate orange (Poncirus trifoliata L.) is one of the most widely utilized rootstocks in citrus production; however, it exhibits a relatively high sensitivity to salt stress. When cultivated in salinized soil, it frequently develops nutrient uptake disorders, leaf chlorosis, as well as reduced fruit yield and quality. To enhance the salt stress tolerance of citrus plants, this study investigated the effects of Trichoderma harzianum inoculation on the growth and response mechanisms of citrus seedlings under salt stress conditions. The results showed that salt stress significantly inhibited the growth of citrus seedlings, while T. harzianum inoculation effectively alleviated the inhibitory effect. After treatment with T. harzianum, the plant height, stem diameter, leaf number, and biomass of citrus seedlings increased significantly. The net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, and chlorophyll content were significantly increased by T. harzianum inoculation. Meanwhile, T. harzianum inoculation increased the content of nitrogen, phosphorus, calcium, magnesium, zinc, and copper, and decreased sodium content in citrus seedlings. In addition, T. harzianum inoculation significantly up-regulated the expression of stress-responsive genes such as SOSs, PIPs, TIP1, TIP4, and TIP9. In conclusion, T. harzianum inoculation improved the salt stress tolerance of citrus seedlings through increasing photosynthetic efficiency, promoting nutrient absorption, sodium efflux, and water utilization via up-regulating the expression of SOSs and aquaporin genes.

Heat stress severely hinders citrus yield and fruit quality. This study employed integrated physiological and transcriptomic analyses to investigate the effects of the exogenous application of abscisic acid (ABA) and brassinosteroid (BR) on heat stress responses in citrus. The results showed that the exogenous application of ABA and BR increased the contents of soluble sugar, proline, and ABA, and enhanced the activities of peroxidase and catalase under heat stress. Transcriptome trend analysis identified profiles 1, 6, and 7 as significantly enriched across exogenous ABA, BR, and control conditions. Profile 6 exhibited rapid upregulation followed by stabilization and showed a significantly higher gene count under both ABA and BR treatments than under the control. KEGG enrichment analysis revealed that genes in profile 6 were primarily enriched in amino sugar, nucleotide sugar, galactose, amino acids, 2-oxocarboxylic acid, glycerophospholipid, glucosinolate metabolism, MAPK signaling pathway, plant hormone signal transduction, protein processing in the endoplasmic reticulum, plant–pathogen interaction, and endocytosis. Furthermore, four genes encoding heat shock proteins (HSP), including HSP21A, HSP21B, HSP70-17, and HSP70A, were induced under heat stress and showed significant upregulation in response to exogenous ABA and BR treatments. In conclusion, these findings indicated that exogenous ABA and BR regulated ABA and osmoprotectant accumulation and antioxidant defense activation in response to heat stress.

Abiotic stresses, including salt stress, drought, extreme temperature, heavy metal pollution, and waterlogging, interfere with the normal physiological activities of plants through multiple pathways. These stresses destroy the structure and function of cell membranes, inhibit enzyme activity, cause protein denaturation, and trigger oxidative stress. Such effects not only slow plant biomass accumulation but may also initiate a series of secondary metabolic reactions, increasing the metabolic burden on plants. Abiotic stress poses a serious threat to agricultural production through yield reductions, while exerting profound negative impacts on ecosystem stability, causing many adverse effects. This review focuses on how Trichoderma promotes plant growth and nutrient uptake through multiple mechanisms under abiotic stress conditions. Additionally, it produces abundant secondary metabolites to activate the antioxidant system, thereby enhancing plant tolerance to abiotic stress and their defense capabilities. It can boost soil nutrient availability, enhance agrochemical-contaminated soil, promote crop growth, and improve yield and quality, while reducing the use of chemical pesticides and lessening environmental impacts. Therefore, as a crucial soil microorganism, Trichoderma has great potential in alleviating crop abiotic stress. Through deep research and technological innovation, Trichoderma is expected to become an important tool for sustainable agricultural development.

Citric acid serves as the principal organic acid in citrus fruits, with its concentration critically determining fruit flavor and market acceptability. Isocitrate dehydrogenase (IDH), a key enzyme in citric acid metabolism, mediates the conversion of citrate to α-ketoglutarate. This study cloned six candidate genes encoding IDH from grapefruit (Citrus paradisi). Bioinformatics analysis showed that all six genes contained the typical characteristic structure of IDH. Gene expression analysis found that CpNADP-IDH1 is highly expressed in mature and low-acid varieties. Overexpression of CpNADP-IDH1 significantly increased IDH enzyme activity and decreased citric acid content in transgenic grapefruit callus. These results showed that at least six genes encoding IDH exist in grapefruit, among which CpNADP-IDH1 catalyzes the decomposition of citric acid and regulates the organic acid content in fruits at maturity. CpNADP-IDH1 can be used as a candidate gene for molecular breeding of low-acid citrus varieties and as an essential target gene for developing citrus cultivation technology for reducing acid content.

Emulsifiable concentrates and oil suspensions are typical pesticide formulations. Many pesticides on the market use aromatic hydrocarbons as solvents. However, studies have revealed their potential risks to humans and the environment. Ethylene glycol diacetate (EGDA) is a low-toxicity and eco-friendly solvent with low utilization in pesticides. This study explores EGDA's potential to replace xylene. Results indicate that EGDA formulations enhance droplet adhesion to leaves, boosting pesticide efficiency. They exhibit lower surface tension and contact angles, with a 24%-40% increase in leaf retention. Bioassays show that 15% cyhalofop-butyl EC and 10% nicosulfuron OF with EGDA offer weed control that is superior to xylene-based formulations by 9.1%-30.5% in greenhouses and 4.8%-6.7% in fields. Xylene preparations are 2-3 times more cytotoxic to human bronchial cells than EGDA-based ones. Thus, EGDA is a promising pesticide solvent, outperforming traditional aromatic solvents in environmental friendliness and reducing adverse effects.

Grafting is a crucial horticultural propagation technique that plays a vital role in citrus production and research. Selecting compatible rootstock–scion combinations is essential for achieving high yields and superior fruit quality in citrus cultivation. This paper reviews recent advances in the physiological and molecular mechanisms involved in rootstock–scion interactions in citrus, with a focus on (1) commonly used rootstocks, (2) graft compatibility, (3) signal molecule transport at the graft union, and (4) the effects of rootstock–scion interactions on citrus growth, nutrient absorption, fruit quality, and responses to both biotic and abiotic stresses. Additionally, we prospected the future research direction and practical applications of rootstock–scion interactions.

Potassium is an essential mineral nutrient for citrus growth and stress response. In this study, the HAK/KUP/KT gene family was identified from the genome of trifoliate orange (Poncirus trifoliata). The physical and chemical properties, chromosomal location, gene structure, evolutionary relationship, conserved motifs, and tissue expression characteristics were analyzed. The expression characteristics under low potassium and salt stress were analyzed by fluorescence quantitative PCR. The function of PtKUP10 was investigated by heterologous expression in Arabidopsis thaliana. The results showed that at least 18 PtKUPs were distributed in seven chromosomes. Phylogenetic analysis showed that four PtKUPs clustered in clade I, which mediated the high-affinity potassium absorption. Gene expression analysis showed that four PtKUPs were highly expressed in root, seven PtKUPs were up-regulated by low potassium stress, and nine PtKUPs were up-regulated by salt stress. The cis-acting elements on the promoter of PtKUPs were predominantly involved in stress and hormone responses. Overexpression of PtKUP10 in Arabidopsis thaliana could enhance salt tolerance by accumulating more potassium in the shoot and reducing sodium content in the shoots and roots. These results indicated that PtKUPs play important roles in potassium absorption and salt stress response, and PtKUP10 might enhance salt tolerance by maintaining potassium and sodium homeostasis.

Facility-forcing cultivation could effectively improve the quality of ‘Beni Madonna’ citrus (Citrus nankao × C. amakusa) and advance the ripening period. However, segment drying (KS) before harvest caused fruit quality deterioration and commodity value loss. In this research, we investigated the physiological and molecular characteristics involved in citrus segment drying under facility-forcing cultivation. The juice yield, sugar, acid, vitamin C, and lignin contents in KS fruits were significantly decreased, and the contents of pectin and cellulose were significantly increased. The relative contents of abscisic acid and abscisic acid glucosyl ester in KS fruits were significantly decreased. A total of 1215 differentially expressed genes (DEGs) were screened by transcriptome sequencing. DEGs were significantly enriched in water metabolism, sugar metabolism, transportation, cell wall and phenylpropanoid biosynthesis, and plant hormone signal transduction. The decrease in water absorption and sugar synthesis, the increase of pectin and cellulose synthesis, and the decrease in ABA accumulation may be the main reasons that cause citrus fruit segments to dry under facility-forcing cultivation.

A Plant Biostimulant is any substance or microorganism applied to plants to enhance nutrition efficiency, abiotic stress tolerance, and/or crop quality traits, regardless of its nutrient content. The application of Plant biostimulants (PBs) in production can reduce the application of traditional pesticides and chemical fertilizers and improve the quality and yield of crops, which is conducive to the sustainable development of agriculture. An in-depth understanding of the mechanism and effect of various PBs is very important for how to apply PBs reasonably and effectively in the practice of crop production. This paper summarizes the main classification of PBs; The growth promotion mechanism of PBs was analyzed from four aspects: improving soil physical and chemical properties, enhancing crop nutrient absorption capacity, photosynthesis capacity, and abiotic stress tolerance; At the same time, the effects of PBs application on seed germination, seedling vigor, crop yield, and quality were summarized; Finally, how to continue to explore and study the use and mechanism of PBs in the future is analyzed and prospected, to better guide the application of PBs in crop production in the future.

Citrus plants exhibit positive floral response under water stress conditions, however, the mechanistic understanding of floral induction remains largely unexplored in water deficit. In this study, DNA methylomic and transcriptomic analyses were integrated to explore the flowering bud formation as well as branches building after light drought stress. While comparing with the conventional watering group (CK), the light drought group treated with five months (LD) showed a significant increase in the flowering branches, whereas an apparent decrease in vegetative branches. Global DNA methylation analysis showed that the LD Group acquired DNA methylation in more than 70,090 genomic regions and lost DNA methylation in about 18,421 genomic regions compared with normal watering group, this indicates that water deficiency leads to a global increase in the expression of DNA methylation in citrus. In the same time, we verified that the increase of DNA methylation level in LD group was correlated with the decrease of DNA demethylase related gene expression. Interestingly, in transcription analysis, it was found that the promoting flower genes of the LD group did not increase but decreased similarly with repressing genes, which is contrary to the intended result. Thus, we thought the lower expression of suppressors FLC and BFT were the key influencing factor to stimulate the flowering branches formation after LD treatment. Moreover, there was a strong negative correlation between the genes expression level and methylation level of the flowering induction/flower development genes. In general, we thought high global DNA methylation level induced by water deficit regulate the flowering branches building by reducing FLC and BFT genes expression.

Protein hydrolysates (PHs) and arbuscular mycorrhizal fungi (AMF) are environmentally friendly biostimulants that effectively promote crop growth and alleviate the damage from abiotic stress. However, the physiological and molecular regulatory mechanisms are still unclear. This study aimed to explore the effects of PHs and AMF on growth, mineral nutrient absorption, and expression of Aquaporins and SOSs in Goutoucheng (Citrus aurantium) under salt stress. Results showed that PH application and AMF inoculation significantly promoted plant growth and enhanced mineral element absorption and sodium effluxion in citrus under salt stress. The biomass, root activity, leaves mineral nutrition contents in PHs, AMF, and combined (PHs and AMF) treatments were significantly higher than those of control. Leaves sodium content in three treatments was significantly lower than in the control. AMF and combined treatments showed dominant effects than PHs alone. Besides, PHs interacted with AMF on growth, nutrient absorption, and sodium effluxion. Importantly, AMF and PHs induced stress-responsive genes. PIP1, PIP3, SOS1, and SOS3 expression in PHs and AMF treatments was significantly higher than control. Thus, it was concluded that AMF and PHs enhanced the salt tolerance of citrus by promoting nutrient absorption and sodium effluxion via up-regulating the expression of PIPs and SOSs. The mixed application of PHs and AMF had a better effect.

To understand the effects of different fertilizer applications on soil quality and arbuscular mycorrhizal colonization, we examined the changes in soil physical and chemical properties, mycorrhizal colonization and propagules, and their relationships in citrus under inorganic fertilization (IF), organic fertilization (OF), combined organic and inorganic fertilization (CF), and no fertilization (CK) treatments. Results showed that all fertilization treatments improved the content of rhizospheric soil organic carbon (SOC), nutrient contents, and electrical conductivity (EC). Both CF and OF significantly increased soil pH, soil aggregate stability, activities of urease, catalase, and sucrase, and the colonization and reproduction of arbuscular mycorrhizae fungi (AMF) in citrus rhizosphere. However, IF treatment significantly decreased soil pH and the colonization and reproduction of AMF in citrus rhizosphere. The number of mycorrhizal colonization and propagation was positively correlated with soil aggregate stability, SOC content, total nitrogen content, total phosphorus content, urease activity, and soil pH. Combined with the principal component analysis, we concluded that application of inorganic fertilizer alone could cause soil acidification and inhibit AMF colonization in citrus orchards. In contrast, organic fertilizer combined with inorganic fertilizer in citrus could improve the soil quality and AMF colonization.

Background Oil palm is the most efficient oil-producing crop in the world, and the yield of palm oil is associated with embryonic development. However, a comprehensive understanding of zygotic embryo development at the molecular level remains elusive. In order to address this issue, we report the transcriptomic analysis of zygotic embryo development in oil palm, specifically focusing on regulatory genes involved in important biological pathways. Results In this study, three cDNA libraries were prepared from embryos at S1 (early-stage), S2 (middle-stage), and S3 (late-stage). There were 16,367, 16,500, and 18,012 genes characterized at the S1, S2, and S3 stages of embryonic development, respectively. A total of 1522, 2698, and 142 genes were differentially expressed in S1 vs S2, S1 vs S3, and S2 vs S3, respectively. Using Gene Ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to identify key genes and pathways. In the hormone signaling pathway, genes related to auxin antagonize the output of cytokinin which regulates the development of embryo meristem. The genes related to abscisic acid negatively regulating the synthesis of gibberellin were strongly up-regulated in the mid-late stage of embryonic development. The results were reported the early synthesis and mid-late degradation of sucrose, as well as the activation of the continuous degradation pathway of temporary starch, providing the nutrients needed for differentiation of the embryonic cell. Moreover, the transcripts of genes involved in fatty acid synthesis were also abundantly accumulated in the zygotic embryos. Conclusion Taken together, our research provides a new perspective on the developmental and metabolic regulation of zygotic embryo development at the transcriptional level in oil palm.

油棕是世界上产油效率最高的热带木本油料作物,其棕榈油产量与合子胚发育密切相关.油棕的合子胚发育是一个系统且复杂的生物过程,其中涉及许多基因的精确调控.MicroRNAs(miRNAs)是重要的信号分子,调节植物的各种发育过程.一些miRNAs已经被整合到基因调控网络中协调植物胚发育的可塑性,但对于其在油棕合子胚发育过程中的作用知之甚少.本研究采用小RNA测序对油棕S1(早期)、S2(中期)和S3(晚期)的合子胚进行高通量测序分析,鉴定了6个已存在的和334个已知的miRNAs,并预测到376个新的miRNAs.其中97、102和19个miRNAs在S1与S2、S1与S3、S2与S3之间差异表达;从S1到S3共有7个miRNAs持续差异表达.另外,miRNAs在调控胚胎早期和晚期的发育差异明显,即与S1相比,S2有36个miRNAs上调和61个miRNAs下调,但与S2相比,S3只有12个miRNAs上调和7个miRNAs下调.依据表达量的变化将135个miRNAs划分为4种趋势,并将对应的938个靶基因与转录组数据进行关联分析,检测到71个miRNA靶基因对.GO富集分析显示7个miRNAs的9个靶基因富集到152个生物过程,且与生长发育相关的基因被鉴定为miRNAs的靶标,表明miRNAs可能在调控油棕胚发育的激素信号、生殖生长等生物学过程中发挥作用.另外,KEGG分析表明miRNAs通过调控次生代谢途径相关基因影响合子胚的成熟.进一步筛选出4个miRNAs家族参与植物激素的合成和信号传导调控:miR159-MYB调控赤霉素和脱落酸来维持胚的发生潜力以及诱导胚成熟,miR 164-NAC调控乙烯和生长素参与胚细胞扩增,miR 172-AP2调控乙烯和脱落酸诱导胚成熟,novel-m004-SPL调控赤霉素来诱导胚的形态建成.本研究初步鉴定了参与油棕合子胚发育相关的miRNAs,为后续研究miRNAs调控合子胚发育的分子机制奠定基础.

油棕(Elaeis guineensis Jacq.)原产非洲,是重要的热带木本油料作物,产油效率极高.目前油棕广泛种植在东南亚、非洲、中南美洲和我国的海南、云南、广东、广西等省(区),油棕果实压榨的棕榈油是重要的食用油和工业原料.脂肪酸在植物质体中合成,然后转运到内质网上进行加工和修饰.为了研究油棕脂肪酸的转运机制,以'热油4号'油棕为研究对象,采用生物信息学和荧光定量PCR挖掘控制油棕脂肪酸转运的关键基因.脂肪酸外运蛋白1(fatty acid export 1,FAX1)是植物脂肪酸转运蛋白,介导细胞内脂肪酸从质体向外运输,在脂质合成中起着重要的调控作用.本研究从油棕中克隆了3个EgFAX1基因(EgFAX1-1,EgFAX1-2,EgFAX1-3,对其氨基酸长度、分子量、等电点、蛋白不稳定指数、脂肪族系数、总平均亲水性、染色体定位、基因结构、保守功能域、进化关系和表达特征进行分析.结果 表明:3个EgFAX1基因编码的肽链氨基酸长度分别为189、231和232,分子量分别为20.43、24.85、24.92 kDa,等电点为分别9.82、9.82和9.93,蛋白不稳定指数分别为48.01、49.71和50.09,脂肪族系数分别为81.06、84.07和83.28,总平均亲水性分别为为0.071、0.121和0.106,分别含有2、5、7个外显子,都含有FAX1的特征结构Tmemb_ 14蛋白结构域.将油棕与拟南芥、水稻、大豆、油菜、番茄、绿藻、红藻、盘藻、团藻、长囊水云、细小微胞藻和小球藻的FAX1氨基酸序列做进化分析,发现EgFAX1与大豆和番茄的亲缘关系较近.采用荧光定量PCR分析3个EgFAX1基因EgFAX1在油棕根、茎、叶、花和果中的表达特征,发现EgFAX1在花和果实中的表达量较高;同时分析3个EgFAX1基因油棕花后15周、17周、21周和23周果实中的表达特征,发现3个EgFAX1基因均在油棕果实发育过程中先升高,到达峰值后逐渐降低,其中EgFAX1-1在花后17周的果实达到峰值,EgFAX1-2和EgFAX1-3在花后21周的果实中达到峰值.本研究为进一步探索EgFAX1调控油棕脂肪酸运输的机制奠定基础.

油脂是植物主要的储能物质,也是植物质膜的重要组分,同时还参与植物信号传导、气孔开闭、授粉受精、种子萌发、胁迫响应等多个生物学过程.WRINKLED 1(WRI1)是AP2转录因子家族的成员,在油脂合成过程中起重要调控作用.本文综述了近年来WRI1在植物油脂合成中的研究进展,主要包括(1)WRI1的发现、起源和进化特征;(2)WRI1的基因表达特征、基因结构、蛋白质结构和启动子顺式作用元件;(3)WRI1的转录水平和翻译水平调控机制以及下游的靶基因;(4)对WRI1后续的研究思路和应用前景进行展望.本综述内容以期为深入了解WRI1调控植物油脂合成的分子机制提供参考,也为利用WRI1改良油料作物提供理论基础.