The SOC1 gene plays an important role in regulating litchi flowering time.

Litchi (Litchi chinensis Sonn.) is a valuable subtropical fruit tree with high-quality fruit. However, its economic benefits and sustainable development are restrained by a number of challenges. One major challenge is the lack of extremely early and late maturing high-quality varieties due to limited availability of varieties suitable for commercial cultivation and outdated breeding methods, resulting in an imbalanced supply and low price of litchi. Flowering time is a crucial genetic factor influencing the maturation period of litchi. Our previous research has highlighted the pivotal role of the LcFT1 gene in regulating the flowering time of litchi and identified a gene associated with LcFT1 (named as LcSOC1) based on RNA-Seq and weight gene co-expression network (WGCNA) analysis. This study further investigated the function of LcSOC1. Subcellular localization analysis revealed that LcSOC1 is primarily localized in the nucleus, where it acts as a transcription factor. LcSOC1 overexpression in Nicotiana tabacum and Arabidopsis thaliana resulted in significant early flowering. Furthermore, LcSOC1 was found to be expressed in various tissues, with the highest expression in mature leaves. Analysis of spatial and temporal expression patterns of LcSOC1 in litchi varieties with different flowering time under low temperature treatment and across an annual cycle demonstrated that LcSOC1 is responsive to low temperature induction. Interestingly, early maturing varieties exhibited higher sensitivity to low temperature, with significantly premature induction of LcSOC1 expression relative to late maturing varieties. Activation of LcSOC1 triggered the transition of litchi into the flowering phase. These findings demonstrate that LcSOC1 plays a pivotal role in regulating the flowering process and determining the flowering time in litchi. Overall, this study provides theoretical guidance and important target genes for molecular breeding to regulate litchi production period.

A LcDOF5.6-LcRbohD regulatory module controls the reactive oxygen species-mediated fruitlet abscission in litchi.

Reactive oxygen species (ROS) have been emerging as a key regulator in plant organ abscission. However, the mechanism underlying the regulation of ROS homeostasis in the abscission zone (AZ) is not completely established. Here, we report that a DOF (DNA binding with one finger) transcription factor LcDOF5.6 can suppress the litchi fruitlet abscission through repressing the ROS accumulation in fruitlet AZ (FAZ). The expression of LcRbohD, a homolog of the Arabidopsis RBOHs that are critical for ROS production, was significantly increased during the litchi fruitlet abscission, in parallel with an increased accumulation of ROS in FAZ. In contrast, silencing of LcRbohD reduced the ROS accumulation in FAZ and decreased the fruitlet abscission in litchi. Using in vitro and in vivo assays, we revealed that LcDOF5.6 was shown to inhibit the expression of LcRbohD via direct binding to its promoter. Consistently, silencing of LcDOF5.6 increased the expression of LcRbohD, concurrently with higher ROS accumulation in FAZ and increased fruitlet abscission. Furthermore, the expression of key genes (LcIDL1, LcHSL2, LcACO2, LcACS1, and LcEIL3) in INFLORESCENCE DEFICIENT IN ABSCISSION signaling and ethylene pathways were altered in LcRbohD-silenced and LcDOF5.6-silenced FAZ cells. Taken together, our results demonstrate an important role of the LcDOF5.6-LcRbohD module during litchi fruitlet abscission. Our findings provide new insights into the molecular regulatory network of organ abscission.

Litchi aspartic protease LcAP1 enhances plant resistance via suppressing cell death triggered by the pectate lyase PlPeL8 from Peronophythora litchii.

Plant cell death is regulated in plant-pathogen interactions. While some aspartic proteases (APs) participate in regulating programmed cell death or defense responses, the defense functions of most APs remain largely unknown. Here, we report on a virulence factor, PlPeL8, which is a pectate lyase found in the hemibiotrophic pathogen Peronophythora litchii. Through in vivo and in vitro assays, we confirmed the interaction between PlPeL8 and LcAP1 from litchi, and identified LcAP1 as a positive regulator of plant immunity. PlPeL8 induced cell death associated with NbSOBIR1 and NbMEK2. The 11 conserved residues of PlPeL8 were essential for inducing cell death and enhancing plant susceptibility. Twenty-three LcAPs suppressed cell death induced by PlPeL8 in Nicotiana benthamiana depending on their interaction with PlPeL8. The N-terminus of LcAP1 was required for inhibiting PlPeL8-triggered cell death and susceptibility. Furthermore, PlPeL8 led to higher susceptibility in NbAPs-silenced N. benthamiana than the GUS-control. Our results indicate the crucial roles of LcAP1 and its homologs in enhancing plant resistance via suppression of cell death triggered by PlPeL8, and LcAP1 represents a promising target for engineering disease resistance. Our study provides new insights into the role of plant cell death in the arms race between plants and hemibiotrophic pathogens.

Transcription factor LcNAC002 coregulates chlorophyll degradation and anthocyanin biosynthesis in litchi.

Chlorophyll degradation and anthocyanin biosynthesis, which often occur almost synchronously during fruit ripening, are crucial for vibrant coloration of fruits. However, the interlink point between their regulatory pathways remains largely unknown. Here, 2 litchi (Litchi chinensis Sonn.) cultivars with distinctively different coloration patterns during ripening, i.e. slow-reddening/stay-green "Feizixiao" (FZX) vs rapid-reddening/degreening "Nuomici" (NMC), were selected as the materials to study the key factors determining coloration. Litchi chinensis STAY-GREEN (LcSGR) was confirmed as the critical gene in pericarp chlorophyll loss and chloroplast breakdown during fruit ripening, as LcSGR directly interacted with pheophorbide a oxygenase (PAO), a key enzyme in chlorophyll degradation via the PAO pathway. Litchi chinensis no apical meristem (NAM), Arabidopsis transcription activation factor 1/2, and cup-shaped cotyledon 2 (LcNAC002) was identified as a positive regulator in the coloration of litchi pericarp. The expression of LcNAC002 was significantly higher in NMC than in FZX. Virus-induced gene silencing of LcNAC002 significantly decreased the expression of LcSGR as well as L. chinensis MYELOBLASTOSIS1 (LcMYB1), and inhibited chlorophyll loss and anthocyanin accumulation. A dual-luciferase reporter assay revealed that LcNAC002 significantly activates the expression of both LcSGR and LcMYB1. Furthermore, yeast-one-hybrid and electrophoretic mobility shift assay results showed that LcNAC002 directly binds to the promoters of LcSGR and LcMYB1. These findings suggest that LcNAC002 is an important ripening-related transcription factor that interlinks chlorophyll degradation and anthocyanin biosynthesis by coactivating the expression of both LcSGR and LcMYB1.

Increased DNA methylation of the splicing regulator SR45 suppresses seed abortion in litchi.

The gene regulatory networks that govern seed development are complex, yet very little is known about the genes and processes that are controlled by DNA methylation. Here, we performed single-base resolution DNA methylome analysis and found that CHH methylation increased significantly throughout seed development in litchi. Based on the association analysis of differentially methylated regions and weighted gene co-expression network analysis (WGCNA), 46 genes were identified as essential DNA methylation-regulated candidate genes involved in litchi seed development, including LcSR45, a homolog of the serine/arginine-rich (SR) splicing regulator SR45. LcSR45 is predominately expressed in the funicle, embryo, and seed integument, and displayed increased CHH methylation in the promoter during seed development. Notably, silencing of LcSR45 in a seed-aborted litchi cultivar significantly improved normal seed development, whereas the ectopic expression of LcSR45 in Arabidopsis caused seed abortion. Furthermore, LcSR45-dependent alternative splicing events were found to regulate genes involved in seed development. Together, our findings demonstrate that LcSR45 is hypermethylated, and plays a detrimental role in litchi seed development, indicating a global increase in DNA methylation at this stage.

Physiological, Metabolic, and Transcriptomic Analyses Reveal Mechanisms of Proliferation and Somatic Embryogenesis of Litchi (Litchi chinensis Sonn.) Embryogenic Callus Promoted by D-Arginine Treatment.

D-arginine (D-Arg) can promote embryogenic callus (EC) proliferation and increase the rate of somatic embryo induction of litchi (Litchi chinensis Sonn.), yet the mechanism underlying the processes is incompletely understood. To investigate the mechanism, physiological responses of polyamines (PAs) [putrescine (Put), spermidine (Spd), and spermine (Spm)] were investigated for D-Arg-treated litchi EC and enzyme activity related to polyamine metabolism, plant endogenous hormones, and polyamine- and embryogenic-related genes were explored. Results showed that the exogenous addition of D-Arg reduces the activity of diamine oxidase (DAO) and polyamine oxidase (PAO) in EC, reduces the production of H2O2, promotes EC proliferation, and increases the (Spd + Spm)/Put ratio to promote somatic embryo induction. Exogenous D-Arg application promoted somatic embryogenesis (SE) by increasing indole-3-acetyl glycine (IAA-Gly), kinetin-9-glucoside (K9G), and dihydrozeatin-7-glucoside (DHZ7G) levels and decreasing trans-zeatin riboside (tZR), N-[(-)-jasmonoyl]-(L)-valine (JA-Val), jasmonic acid (JA), and jasmonoyl-L-isoleucine (Ja-ILE) levels on 18 d, as well as promoting cell division and differentiation. The application of exogenous D-Arg regulated EC proliferation and somatic embryo induction by altering gene expression levels of the WRKY family, AP2/ERF family, C3H family, and C2H2 family. These results indicate that exogenous D-Arg could regulate the proliferation of EC and the SE induction of litchi by changing the biosynthesis of PAs through the alteration of gene expression pattern and endogenous hormone metabolism.

Genome-Wide Identification and Expression Analysis of the Class III Peroxidase Gene Family under Abiotic Stresses in Litchi (Litchi chinensis Sonn.).

Class III peroxidases (CIII PRXs) are plant-specific enzymes with high activity that play key roles in the catalysis of oxidation-reduction reactions. In plants, CIII PRXs can reduce hydrogen peroxide to catalyze oxidation-reduction reactions, thereby affecting plant growth, development, and stress responses. To date, no systematic analysis of the CIII PRX gene family in litchi (Litchi chinensis Sonn.) has been documented, although the genome has been reported. In this study, a total of 77 CIII PRX (designated LcPRX) gene family members were predicted in the litchi genome to provide a reference for candidate genes in the responses to abiotic stresses during litchi growth and development. All of these LcPRX genes had different numbers of highly conserved PRX domains and were unevenly distributed across fifteen chromosomes. They were further clustered into eight clades using a phylogenetic tree, and almost every clade had its own unique gene structure and motif distribution. Collinearity analysis confirmed that there were eleven pairs of duplicate genes among the LcPRX members, and segmental duplication (SD) was the main driving force behind the LcPRX gene expansion. Tissue-specific expression profiles indicated that the expression levels of all the LcPRX family members in different tissues of the litchi tree were significantly divergent. After different abiotic stress treatments, quantitative real-time PCR (qRT-PCR) analysis revealed that the LcPRX genes responded to various stresses and displayed differential expression patterns. Physicochemical properties, transmembrane domains, subcellular localization, secondary structures, and cis-acting elements were also analyzed. These findings provide insights into the characteristics of the LcPRX gene family and give valuable information for further elucidating its molecular function and then enhancing abiotic stress tolerance in litchi through molecular breeding.

Genome-Wide Characterization and Phylogenetic and Stress Response Expression Analysis of the MADS-Box Gene Family in Litchi (Litchi chinensis Sonn.).

The MADS-box protein is an important transcription factor in plants and plays an important role in regulating the plant abiotic stress response. In this study, a total of 94 MADS-box genes were predicted in the litchi genome, and these genes were widely distributed on all the chromosomes. The LcMADS-box gene family was divided into six subgroups (Mα, Mß, Mγ, Mδ, MIKC, and UN) based on their phylogenetical relationships with Arabidopsis, and the closely linked subgroups exhibited more similarity in terms of motif distribution and intron/exon numbers. Transcriptome analysis indicated that LcMADS-box gene expression varied in different tissues, which can be divided into universal expression and specific expression. Furthermore, we further validated that LcMADS-box genes can exhibit different responses to various stresses using quantitative real-time PCR (qRT-PCR). Moreover, physicochemical properties, subcellular localization, collinearity, and cis-acting elements were also analyzed. The findings of this study provide valuable insights into the MADS-box gene family in litchi, specifically in relation to stress response. The identification of hormone-related and stress-responsive cis-acting elements in the MADS-box gene promoters suggests their involvement in stress signaling pathways. This study contributes to the understanding of stress tolerance mechanisms in litchi and highlights potential regulatory mechanisms underlying stress responses.

The transcriptional control of LcIDL1-LcHSL2 complex by LcARF5 integrates auxin and ethylene signaling for litchi fruitlet abscission.

At the physiological level, the interplay between auxin and ethylene has long been recognized as crucial for the regulation of organ abscission in plants. However, the underlying molecular mechanisms remain unknown. Here, we identified transcription factors involved in indoleacetic acid (IAA) and ethylene (ET) signaling that directly regulate the expression of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) and its receptor HAESA (HAE), which are key components initiating abscission. Specifically, litchi IDA-like 1 (LcIDL1) interacts with the receptor HAESA-like 2 (LcHSL2). Through in vitro and in vivo experiments, we determined that the auxin response factor LcARF5 directly binds and activates both LcIDL1 and LcHSL2. Furthermore, we found that the ETHYLENE INSENSITIVE 3-like transcription factor LcEIL3 directly binds and activates LcIDL1. The expression of IDA and HSL2 homologs was enhanced in LcARF5 and LcEIL3 transgenic Arabidopsis plants, but reduced in ein3 eil1 mutants. Consistently, the expressions of LcIDL1 and LcHSL2 were significantly decreased in LcARF5- and LcEIL3-silenced fruitlet abscission zones (FAZ), which correlated with a lower rate of fruitlet abscission. Depletion of auxin led to an increase in 1-aminocyclopropane-1-carboxylic acid (the precursor of ethylene) levels in the litchi FAZ, followed by abscission activation. Throughout this process, LcARF5 and LcEIL3 were induced in the FAZ. Collectively, our findings suggest that the molecular interactions between litchi AUXIN RESPONSE FACTOR 5 (LcARF5)-LcIDL1/LcHSL2 and LcEIL3-LcIDL1 signaling modules play a role in regulating fruitlet abscission in litchi and provide a long-sought mechanistic explanation for how the interplay between auxin and ethylene is translated into the molecular events that initiate abscission.

Asymmetric distribution of mineral nutrients aggravates uneven fruit pigmentation driven by sunlight exposure in litchi.

MAIN CONCLUSION: Sunlight boosts anthocyanin synthesis/accumulation in sunny pericarp of litchi fruit, directly leading to uneven pigmentation. Distribution discrepancy of mineral element aggravates uneven coloration by modulating synthesis/accumulation of anthocyanin and sugar. Uneven coloration, characterized by red pericarp on sunny side and green pericarp on shady side, impacts fruit quality of 'Feizixiao' (cv.) litchi. The mechanisms of this phenomenon were explored by investigating the distribution of chlorophyll, flavonoids, sugars, and mineral elements in both types of pericarp. Transcriptome analysis in pericarp was conducted as well. Sunny pericarp contained higher anthocyanins in an order of magnitude and higher fructose, glucose, co-pigments (flavanols, flavonols, ferulic acid), and mineral elements like Ca, Mg and Mn, along with lower N, P, K, S, Cu, Zn and B (P < 0.01), compared to shady pericarp. Sunlight regulated the expression of genes involved in synthesis/accumulation of flavonoids and sugars and genes functioning in nutrient uptake and transport, leading to asymmetric distribution of these substances. Anthocyanins conferred red color on sunny pericarp, sugars, Ca and Mg promoted synthesis/accumulation of anthocyanins, and co-pigments enhanced color display of anthocyanins. The insufficiencies of anthocyanins, sugars and co-pigments, and inhibition effect of excess K, S, N and P on synthesis/accumulation of anthocyanins and sugars, jointly contributed to green color of shady pericarp. These findings highlight the role of asymmetric distribution of substances, mineral elements in particular, on uneven pigmentation in litchi, and provide insights into coloration improvement via precise fertilization.

Integrated metabolome and transcriptome analysis reveals the cause of anthocyanin biosynthesis deficiency in litchi aril.

Anthocyanins are health-promoting compounds with strong antioxidant properties that play important roles in disease prevention. Litchi chinensis Sonn. is a well-known and economically significant fruit due to its appealing appearance and nutritional value. The mature pericarp of litchi is rich in anthocyanins, whereas the aril (flesh) has an extremely low anthocyanin content. However, the mechanism of anthocyanin differential accumulation in litchi pericarp and aril remained unknown. Here, metabolome and transcriptome analysis were performed to unveil the cause of the deficiency of anthocyanin biosynthesis in litchi aril. Numerous anthocyanin biosynthesis-related metabolites and their derivatives were found in the aril, and the levels of rutin and (-)-epicatechin in the aril were comparable to those found in the pericarp, while anthocyanin levels were negligible. This suggests that the biosynthetic pathway from phenylalanine to cyanidin was present but that a block in cyanidin glycosylation could result in extremely low anthocyanin accumulation in the aril. Furthermore, 54 candidate genes were screened using weighted gene co-expression network analysis (WGCNA), and 9 genes (LcUFGT1, LcGST1, LcMYB1, LcSGR, LcCYP75B1, LcMATE, LcTPP, LcSWEET10, and LcERF61) might play a significant role in regulating anthocyanin biosynthesis. The dual-luciferase reporter (DLR) assay revealed that LcMYB1 strongly activated the promoters of LcUFGT1, LcGST4, and LcSWEET10. The results imply that LcMYB1 is the primary qualitative gene responsible for the deficiency of anthocyanin biosynthesis in litchi aril, which was confirmed by a transient transformation assay. Our findings shed light on the molecular mechanisms underlying tissue-specific anthocyanin accumulation and will help developing new red-fleshed litchi germplasm.

An LcMYB111-LcHY5 Module Differentially Activates an LcFLS Promoter in Different Litchi Cultivars.

Flavonol synthase (FLS) is the crucial enzyme of the flavonol biosynthetic pathways, and its expression is tightly regulated in plants. In our previous study, two alleles of LcFLS,LcFLS-A and LcFLS-B, have been identified in litchi, with extremely early-maturing (EEM) cultivars only harboring LcFLS-A, while middle-to-late-maturing (MLM) cultivars only harbor LcFLS-B. Here, we overexpressed both LcFLS alleles in tobacco, and transgenic tobacco produced lighter-pink flowers and showed increased flavonol levels while it decreased anthocyanin levels compared to WT. Two allelic promoters of LcFLS were identified, with EEM cultivars only harboring proLcFLS-A, while MLM cultivars only harbor proLcFLS-B. One positive and three negative R2R3-MYB transcription regulators of LcFLS expression were identified, among which only positive regulator LcMYB111 showed a consistent expression pattern with LcFLS, which both have higher expression in EEM than that of MLM cultivars. LcMYB111 were further confirmed to specifically activate proLcFLS-A with MYB-binding element (MBE) while being unable to activate proLcFLS-B with mutated MBE (MBEm). LcHY5 were also identified and can interact with LcMYB111 to promote LcFLS expression. Our study elucidates the function of LcFLS and its differential regulation in different litchi cultivars for the first time.

Genome-wide identification and expression analysis of carotenoid cleavage oxygenase genes in Litchi (Litchi chinensis Sonn.).

BACKGROUND: Carotenoid cleavage oxygenases (CCOs) include the carotenoid cleavage dioxygenase (CCD) and 9-cis-epoxycarotenoid (NCED), which can catalize carotenoid to form various apocarotenoids and their derivatives, has been found that play important role in the plant world. But little information of CCO gene family has been reported in litchi (Litchi chinensis Sonn.) till date. RESULTS: In this study, a total of 15 LcCCO genes in litchi were identified based on genome wide lever. Phylogeny analysis showed that LcCCO genes could be classified into six subfamilies (CCD1, CCD4, CCD7, CCD8, CCD-like, and NCED), which gene structure, domain and motifs exhibited similar distribution patterns in the same subfamilies. MiRNA target site prediction found that there were 32 miRNA target sites in 13 (86.7%) LcCCO genes. Cis-elements analysis showed that the largest groups of elements were light response related, following was plant hormones, stress and plant development related. Expression pattern analysis revealed that LcCCD4, LcNCED1, and LcNCED2 might be involving with peel coloration, LcCCDlike-b might be an important factor deciding fruit flavor, LcNCED2 and LcNCED3 might be related to flower control, LcNCED1 and LcNCED2 might function in fruitlet abscission, LcCCD4a1, LcCCD4a2, LcCCD1, LcCCD4, LcNCED1, and LcNCED2 might participate in postharvest storage of litchi. CONCLUSION: Herein, Genome-wide analysis of the LcCCO genes was conducted in litchi to investigate their structure features and potential functions. These valuable and expectable information of LcCCO genes supplying in this study will offer further more possibility to promote quality improvement and breeding of litchi and further function investigation of this gene family in plant.

Organic mulch can suppress litchi downy blight through modification of soil microbial community structure and functional potentials.

BACKGROUND: Organic mulch is an important management practice in agricultural production to improve soil quality, control crop pests and diseases and increase the biodiversity of soil microecosystem. However, the information about soil microbial diversity and composition in litchi plantation response to organic mulch and its attribution to litchi downy blight severity was limited. This study aimed to investigate the effect of organic mulch on litchi downy blight, and evaluate the biodiversity and antimicrobial potential of soil microbial community of litchi plantation soils under organic mulch. RESULTS: Organic mulch could significantly suppress the disease incidence in the litchi plantation, and with a reduction of 37.74% to 85.66%. As a result of high-throughput 16S rRNA and ITS rDNA gene illumine sequencing, significantly higher bacterial and fungal community diversity indexes were found in organic mulch soils, the relative abundance of norank f norank o Vicinamibacterales, norank f Vicinamibacteraceae, norank f Xanthobacteraceae, Unclassified c sordariomycetes, Aspergillus and Thermomyces were significant more than that in control soils. Isolation and analysis of antagonistic microorganism showed that 29 antagonistic bacteria strains and 37 antagonistic fungi strains were unique for mulching soils. CONCLUSIONS: Thus, we believe that organic mulch has a positive regulatory effect on the litchi downy blight and the soil microbial communities, and so, is more suitable for litchi plantation.

Metabolome and transcriptome analysis of terpene synthase genes and their putative role in floral aroma production in Litchi chinensis.

Volatile organic compounds (VOCs) are essential traits of flowers since they attract pollinators, aid in seed distribution, protect the plant from internal and external stimuli, and are involved in plant-plant and plant-environment interactions. Apart from their role in plants, VOCs are used in pharmaceuticals, fragrances, cosmetics, and flavorings. Litchi (Litchi chinensis Sonn.) is a popular fruit due to its enticing red appearance, exotic taste, and high nutritional qualities. Litchi flowers bloom as inflorescences primarily on the shoot terminals. There are three distinct flower types, two male and one female, all of which are produced on the same panicle and rely on insect pollination. Herein, we used a comprehensive metabolomic approach to examine the volatile profile of litchi fruit (green pericarp, yellow pericarp, and red pericarp) as well as male and female flowers (bud stage, half open and full bloom). From a quantitative examination of the volatiles in L. chinensis, a total of 19, 22, and 21 VOCs were discovered from female flowers, male flowers, and fruits, with the majority of them belonging to sesquiterpenes. Multivariate analysis revealed that the volatile profiles of fruits differ from those of male and female flowers. Three VOCs were unique to male flowers and ten to the fruit, while eight VOCs were shared by both male and female flowers and eleven by both male and female flowers and the fruit. Furthermore, for the first time, we identified and comprehensively studied the TERPENE SYNTHASE genes (TPS) using the litchi genome and transcriptome database, which revealed 38 TPS genes unevenly distributed across the 15 chromosomes. A phylogenetic study showed that LcTPS were grouped into TPS-b, TPS-c, TPS-e, TPS-f, and TPS-g subfamilies, with TPS-b having the most genes. The conserved motifs (RRX8 W, NSE/DTE, and DDXX D) were studied in LcTPSs, and significant variation between subfamilies was discovered. Furthermore, after integrating the metabolome and transcriptome datasets, several VOCs were shown to be development-specific and highly linked with distinct LcTPS genes, making them promising biomarkers. Interestingly, LcTPS17/20/23/24/31 were associated with monoterpene edges, while the rest were connected to sesquiterpene edges, indicating their probable participation in the aroma biosynthesis mechanism of certain compounds.

A C2H2 Zinc Finger Protein PlCZF1 Is Necessary for Oospore Development and Virulence in Peronophythora litchii.

C2H2 zinc finger is one of the most common motifs found in the transcription factors (TFs) in eukaryotes organisms, which have a broad range of functions, such as regulation of growth and development, stress tolerance and pathogenicity. Here, PlCZF1 was identified to encode a C2H2 zinc finger in the litchi downy blight pathogen Peronophythora litchii. PlCZF1 is conserved in P. litchii and Phytophthora species. In P. litchii, PlCZF1 is highly expressed in sexual developmental and early infection stages. We generated Δplczf1 mutants using the CRISPR/Cas9 method. Compared with the wild type, the Δplczf1 mutants showed no significant difference in vegetative growth and asexual reproduction, but were defective in oospore development and virulence. Further experiments revealed that the transcription of PlM90, PlLLP and three laccase encoding genes were down-regulated in the Δplczf1 mutant. Our results demonstrated that PlCZF1 is a vital regulator for sexual development and pathogenesis in P. litchii.

Identification of Chilling-Responsive Genes in Litchi chinensis by Transcriptomic Analysis Underlying Phytohormones and Antioxidant Systems.

Litchi (Litchi chinensis Sonn.) is an important subtropical and tropical evergreen fruit tree that is seriously affected by chilling stress. In order to identify genes that may be involved in the response to chilling in litchi, we investigate the physiological and biochemical changes under chilling stress and construct 12 RNA-Seq libraries of leaf samples at 0, 4, 8, and 12 days of chilling. The results show that antioxidant enzymes are activated by chilling treatments. Comparing the transcriptome data of the four time points, we screen 2496 chilling-responsive genes (CRGs), from which we identify 63 genes related to the antioxidant system (AO-CRGs) and 54 ABA, 40 IAA, 37 CTK, 27 ETH, 21 BR, 13 GA, 35 JA, 29 SA, and 4 SL signal transduction-related genes. Expression pattern analysis shows that the expression trends of the 28 candidate genes detected by qRT-PCR are similar to those detected by RNA-Seq, indicating the reliability of our RNA-Seq data. Partial Least Squares Structural Equation Modeling (PLS-SEM) analysis of the RNA-Seq data suggests a model for the litchi plants in response to chilling stress that alters the expression of the plant hormone signaling-related genes, the transcription factor-encoding genes LcICE1, LcCBFs, and LcbZIPs, and the antioxidant system-related genes. This study provides candidate genes for the future breeding of litchi cultivars with high chilling resistance, and elucidates possible pathways for litchi in response to chilling using transcriptomic data.

Genome Sequence Data of Peronophythora litchii, an Oomycete Pathogen Causing Litchi Downy Blight.

Peronophythora litchii is an oomycete pathogen that exclusively infects litchi, with infection stages affecting a broad range of tissues. In this study, we obtained a near chromosome-level genome assembly of P. litchii ZL2018 from China using Oxford Nanopore Technologies long-read sequencing and Illumina short-read sequencing. The genome assembly was 64.15 Mb in size and consisted of 81 contigs with an N50 of 1.43 Mb and a maximum length of 4.74 Mb. Excluding 34.67% of repeat sequences, 14,857 protein-coding genes were identified, among which 14,447 genes were annotated. We also predicted 306 candidate RxLR effectors in the assembly. The high-quality genome assembly and annotation resources reported in this study will provide new insight into the infection mechanisms of P. litchii.[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. 2021.

The GRAS gene family and its roles in seed development in litchi (Litchi chinensis Sonn).

BACKGROUND: The GRAS gene family plays crucial roles in multiple biological processes of plant growth, including seed development, which is related to seedless traits of litchi (Litchi chinensis Sonn.). However, it hasn't been fully identified and analyzed in litchi, an economic fruit tree cultivated in subtropical regions. RESULTS: In this study, 48 LcGRAS proteins were identified and termed according to their chromosomal location. LcGRAS proteins can be categorized into 14 subfamilies through phylogenetic analysis. Gene structure and conserved domain analysis revealed that different subfamilies harbored various motif patterns, suggesting their functional diversity. Synteny analysis revealed that the expansion of the GRAS family in litchi may be driven by their tandem and segmental duplication. After comprehensively analysing degradome data, we found that four LcGRAS genes belong to HAM subfamily were regulated via miR171-mediated degradation. The various expression patterns of LcGRAS genes in different tissues uncovered they were involved in different biological processes. Moreover, the different temporal expression profiles of LcGRAS genes between abortive and bold seed indicated some of them were involved in maintaining the normal development of the seed. CONCLUSION: Our study provides comprehensive analyses on GRAS family members in litchi, insight into a better understanding of the roles of GRAS in litchi development, and lays the foundation for further investigations on litchi seed development.

Xyloglucan endotransglucosylase/hydrolase genes LcXTH4/7/19 are involved in fruitlet abscission and are activated by LcEIL2/3 in litchi.

Organ abscission in plants requires the hydrolysis of cell wall components, mainly including celluloses, pectins, and xyloglucans. However, how the genes that encode those hydrolytic enzymes are regulated and their function in abscission remains unclear. Previously we revealed that two cellulase genes LcCEL2/8 and two polygalacturonase genes LcPG1/2 were responsible for the degradation of celluloses and pectins, respectively, during fruitlet abscission in litchi. Here, we further identified three xyloglucan endotransglucosylase/hydrolase genes (LcXTH4, LcXTH7, LcXTH19) that are also involved in this process. Nineteen LcXTHs, named LcXTH1-19, were identified in the litchi genome. Transcriptome data and qRT-PCR confirmed that LcXTH4/7/19 were significantly induced at the abscission zone (AZ) during fruitlet abscission in litchi. The GUS reporter driven by each promoter of LcXTH4/7/19 was specifically expressed at the floral abscission zone of Arabidopsis, and importantly ectopic expression of LcXTH19 in Arabidopsis resulted in precocious floral organ abscission. Moreover, electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter analysis showed that the expression of LcXTH4/7/19 could be directly activated by two ETHYLENE INSENSITIVE 3-like (EIL) transcription factors LcEIL2/3. Collectively, we propose that LcXTH4/7/19 are involved in fruitlet abscission, and LcEIL2/3-mediated transcriptional regulation of diverse cell wall hydrolytic genes is responsible for this process in litchi.