The ethylene response factor gene, ThDRE1A, is involved in abscisic acid- and ethylene-mediated cadmium accumulation in Tamarix hispida.

Tamarix hispida is highly tolerant to salt, drought and heavy metal stress and is a potential material for the remediation of cadmium (Cd)-contaminated soil under harsh conditions. In this study, T. hispida growth and chlorophyll content decreased, whereas flavonoid and carotenoid contents increased under long-term Cd stress (25 d). The aboveground components of T. hispida were collected for RNA-seq to investigate the mechanism of Cd accumulation. GO and KEGG enrichment analyses revealed that the differentially expressed genes (DEGs) were significantly enriched in plant hormone-related pathways. Exogenous hormone treatment and determination of Cd2+ levels showed that ethylene (ETH) and abscisic acid (ABA) antagonists regulate Cd accumulation in T. hispida. Twenty-five transcription factors were identified as upstream regulators of hormone-related pathways. ThDRE1A, which was previously identified as an important regulatory factor, was selected for further analysis. The results indicated that ThABAH2.5 and ThACCO3.1 were direct target genes of ThDRE1A. The determination of Cd2+, ABA, and ETH levels indicated that ThDRE1A plays an important role in Cd accumulation through the antagonistic regulation of ABA and ETH. In conclusion, these results reveal the molecular mechanism underlying Cd accumulation in plants and identify candidate genes for further research.

The key pathways for drought tolerance in Cerasus humilis were unveiled through transcriptome analysis.

Drought stress exerts a significant impact on the growth, development, and yield of fruit trees. Cerasus humilis is an endemic drought-resistant fruit tree in northern China. To elucidate the underlying mechanism of drought resistance in C. humilis, comprehensive physiological measurements and transcriptome analysis were conducted on the leaves of C. humilis subjected to 15- or 22-days of drought stress. We identified multiple GO terms and KEGG pathways associated with the drought stress response by performing GO and KEGG analysis on DEGs. Furthermore, through the prediction of transcription factors (TFs) and analysis of their expression levels, we observed differential expression patterns among most members of stress-responsive TF families as the duration of drought stress increased. WGCNA analysis was performed on the transcriptome to identify gene cluster modules that exhibited a strong correlation with the durations of drought. Subsequently, these modules underwent GO and KEGG enrichment analyses. The study revealed that the TF-mediated lignin biosynthesis pathway, along with the plant hormone signal transduction pathway, played a prominent role in responding to drought stress of C. humilis. Gene profiling analysis, qRT-PCR, and determination of phytohormone and lignin contents further supported this hypothesis. The hierarchical gene regulatory network was finally constructed based on DEGs from the aforementioned key enriched pathways to predict the gene regulatory mechanisms in response to stress for C. humilis. The findings from this study provide valuable insights into how C. humilis copes with drought stress while analyzing crucial gene pathways associated with its resistance from a TF perspective. This research is significant for the genetic breeding of economic forests.

Brassinosteroid-dependent phosphorylation of PHOSPHATE STARVATION RESPONSE2 reduces its DNA-binding ability in rice.

Brassinosteroids (BRs) are widely used as plant growth regulators in modern agriculture. Understanding how BRs regulate nutrient signaling is crucial for reducing fertilizer usage. Here we elucidate that the central BR signaling inhibitor GSK3/SHAGGY-LIKE KINASE2 (GSK2) interacts directly with and phosphorylates PHOSPHATE STARVATION RESPONSE2 (OsPHR2), the key regulator of phosphate (Pi) signaling, to suppress its transcription factor activity in rice (Oryza sativa). We identify a critical phosphorylation site at serine residue S269 of OsPHR2 and demonstrate that phosphorylation by GSK2 or phosphor-mimic mutation of S269 substantially impairs the DNA-binding activity of OsPHR2, and thus diminishes expression of OsPHR2-induced genes and reduces Pi levels. Like BRs, Pi starvation noticeably induces GSK2 instability. We further show that this site-specific phosphorylation event is conserved in Arabidopsis (Arabidopsis thaliana), but varies among the PHR-family members, being present only in most land plants. These results unveil a distinctive post-transcriptional regulatory mechanism in Pi signaling by which BRs promote Pi acquisition, with a potential contribution to the environmental adaptability of plants during their evolution.

BpGRP1 acts downstream of BpmiR396c/BpGRF3 to confer salt tolerance in Betula platyphylla.

Glycine-rich RNA-binding proteins (GRPs) have been implicated in the responses of plants to environmental stresses, but the function of GRP genes involved in salt stress and the underlying mechanism remain unclear. In this study, we identified BpGRP1 (glycine-rich RNA-binding protein), a Betula platyphylla gene that is induced under salt stress. The physiological and molecular responses to salt tolerance were investigated in both BpGRP1-overexpressing and suppressed conditions. BpGRF3 (growth-regulating factor 3) was identified as a regulatory factor upstream of BpGRP1. We demonstrated that overexpression of BpGRF3 significantly increased the salt tolerance of birch, whereas the grf3-1 mutant exhibited the opposite effect. Further analysis revealed that BpGRF3 and its interaction partner, BpSHMT, function upstream of BpGRP1. We demonstrated that BpmiR396c, as an upstream regulator of BpGRF3, could negatively regulate salt tolerance in birch. Furthermore, we uncovered evidence showing that the BpmiR396c/BpGRF3 regulatory module functions in mediating the salt response by regulating the associated physiological pathways. Our results indicate that BpmiR396c regulates the expression of BpGRF3, which plays a role in salt tolerance by targeting BpGRP1.

Rhabdovirus encoded glycoprotein induces and harnesses host antiviral autophagy for maintaining its compatible infection.

Macroautophagy/autophagy has been recognized as a central antiviral defense mechanism in plant, which involves complex interactions between viral proteins and host factors. Rhabdoviruses are single-stranded RNA viruses, and the infection causes serious harm to public health, livestock, and crop production. However, little is known about the role of autophagy in the defense against rhabdovirus infection by plant. In this work, we showed that Rice stripe mosaic cytorhabdovirus(RSMV) activated autophagy in plants and that autophagy served as an indispensable defense mechanism during RSMV infection. We identified RSMV glycoprotein as an autophagy inducer that interacted with OsSnRK1B and promoted the kinase activity of OsSnRK1B on OsATG6b. RSMV glycoprotein was toxic to rice cells and its targeted degradation by OsATG6b-mediated autophagy was essential to restrict the viral titer in plants. Importantly, SnRK1-glycoprotein and ATG6-glycoprotein interactions were well-conserved between several other rhabdoviruses and plants. Together, our data support a model that SnRK1 senses rhabdovirus glycoprotein for autophagy initiation, while ATG6 mediates targeted degradation of viral glycoprotein. This conserved mechanism ensures compatible infection by limiting the toxicity of viral glycoprotein and restricting the infection of rhabdoviruses.Abbreviations: AMPK: adenosine 5'-monophosphate (AMP)-activated protein kinase; ANOVA: analysis of variance; ATG: autophagy related; AZD: AZD8055; BiFC: bimolecular fluorescence complementation; BYSMV: barley yellow striate mosaic virus; Co-IP: co-immunoprecipitation; ConA: concanamycin A; CTD: C-terminal domain; DEX: dexamethasone; DMSO: dimethyl sulfoxide; G: glycoprotein; GFP: green fluorescent protein; MD: middle domain; MDC: monodansylcadaverine; NTD: N-terminal domain; OE: over expression; Os: Oryza sativa; PBS: phosphate-buffered saline; PtdIns3K: class III phosphatidylinositol-3-kinase; qRT-PCR: quantitative real-time reverse-transcription PCR; RFP: red fluorescent protein; RSMV: rice stripe mosaic virus; RSV: rice stripe virus; SGS3: suppressor of gene silencing 3; SnRK1: sucrose nonfermenting1-related protein kinase1; SYNV: sonchus yellow net virus; TEM: transmission electron microscopy; TM: transmembrane region; TOR: target of rapamycin; TRV: tobacco rattle virus; TYMaV: tomato yellow mottle-associated virus; VSV: vesicular stomatitis virus; WT: wild type; Y2H: yeast two-hybrid; YFP: yellow fluorescent protein.

Bp-miR408a participates in osmotic and salt stress responses by regulating BpBCP1 in Betula platyphylla.

The microRNAs, which are small RNAs of 18-25 nt in length, act as key regulatory factors in posttranscriptional gene expression during plant growth and development. However, little is known about their regulatory roles in response to stressful environments in birch (Betula platyphylla). Here, we characterized and further explored miRNAs from osmotic- and salt-stressed birch. Our analysis revealed a total of 190 microRNA (miRNA) sequences, which were classified into 180 conserved miRNAs and 10 predicted novel miRNAs based on sequence homology. Furthermore, we identified Bp-miR408a under osmotic and salt stress and elucidated its role in osmotic and salt stress responses in birch. Notably, under osmotic and salt stress, Bp-miR408a contributed to osmotic and salt tolerance sensitivity by mediating various physiological changes, such as increases in reactive oxygen species accumulation, osmoregulatory substance contents and Na+ accumulation. Additionally, molecular analysis provided evidence of the in vivo targeting of BpBCP1 (blue copper protein) transcripts by Bp-miR408a. The overexpression of BpBCP1 in birch enhanced osmotic and salt tolerance by increasing the antioxidant enzyme activity, maintaining cellular ion homeostasis and decreasing lipid peroxidation and cell death. Thus, we reveal a Bp-miR408a-BpBCP1 regulatory module that mediates osmotic and salt stress responses in birch.

An Insight of Betula platyphylla SWEET Gene Family through Genome-Wide Identification, Expression Profiling and Function Analysis of BpSWEET1c under Cold Stress.

SWEET proteins play important roles in plant growth and development, sugar loading in phloem and resistance to abiotic stress through sugar transport. In this study, 13 BpSWEET genes were identified from birch genome. Collinearity analysis showed that there were one tandem repeating gene pair (BpSWEET1b/BpSWEET1c) and two duplicative gene pairs (BpSWEET17a/BpSWEET17b) in the BpSWEET gene family. The BpSWEET gene promoter regions contained several cis-acting elements related to stress resistance, for example: hormone-responsive and low-temperature-responsive cis-elements. Analysis of transcriptome data showed that BpSWEET genes were highly expressed in several sink organs, and the most BpSWEET genes were rapidly up-regulated under cold stress. BpSWEET1c, which was highly expressed in cold stress, was selected for further analysis. It was found that BpSWEET1c was located on the cell membrane. After 6 h of 4 °C stress, sucrose content in the leaves and roots of transient overexpressed BpSWEET1c was significantly higher than that of the control. MDA content in roots was significantly lower than that of the control. These results indicate that BpSWEET1c may play a positive role in the response to cold stress by promoting the metabolism and transport of sucrose. In conclusion, 13 BpSWEET genes were identified from the whole genome level. Most of the SWEET genes of birch were expressed in the sink organs and could respond to cold stress. Transient overexpression of BpSWEET1c changed the soluble sugar content and improved the cold tolerance of birch.

Dynamic monitoring of TGW6 by selective autophagy during grain development in rice.

Crop yield must increase to achieve food security in the face of a growing population and environmental deterioration. Grain size is a prime breeding target for improving grain yield and quality in crop. Here, we report that autophagy emerges as an important regulatory pathway contributing to grain size and quality in rice. Mutations of rice Autophagy-related 9b (OsATG9b) or OsATG13a causes smaller grains and increase of chalkiness, whereas overexpression of either promotes grain size and quality. We also demonstrate that THOUSAND-GRAIN WEIGHT 6 (TGW6), a superior allele that regulates grain size and quality in the rice variety Kasalath, interacts with OsATG8 via the canonical Atg8-interacting motif (AIM), and then is recruited to the autophagosome for selective degradation. In consistent, alteration of either OsATG9b or OsATG13a expression results in reciprocal modulation of TGW6 abundance during grain growth. Genetic analyses confirmed that knockout of TGW6 in either osatg9b or osatg13a mutants can partially rescue their grain size defects, indicating that TGW6 is one of the substrates for autophagy to regulate grain development. We therefore propose a potential framework for autophagy in contributing to grain size and quality in crops.

Comparative transcriptomic and metabolomic analyses provide insights into the responses to NaCl and Cd stress in Tamarix hispida.

Salinity and heavy metal pollution seriously affect plant growth. Tamarix hispida (T. hispida) has the potential to remediate soil saline-alkali and heavy metal pollution. In this study, the response mechanisms of T. hispida under NaCl, CdCl2 (Cd) and combined CdCl2 and NaCl (Cd-NaCl) stresses were explored. Overall, the antioxidant system showed changes under the three stresses. The addition of NaCl inhibited the absorption of Cd2+. However, there were obvious differences in the transcripts and metabolites identified among the three stress responses. Interestingly, the number of DEGs was greatest under NaCl stress (929), but the number of differentially expressed metabolites (DEMs) was lowest (48), with 143 and 187 DEMs identified under Cd and Cd-NaCl stress, respectively. It is worth noting that both DEGs and DEMs were enriched in the linoleic acid metabolism pathway under Cd stress. In particular, the content of lipids changed significantly under Cd and Cd-NaCl stress, suggesting that maintaining normal lipid synthesis and metabolism may be an important way to improve the Cd tolerance of T. hispida. Flavonoids may also play an important role in the response to NaCl and Cd stress. These results provide a theoretical basis for cultivating plants with improved salt and cadmium repair abilities.

Genome-wide identification and expression profiling of the bZIP gene family in Betula platyphylla and the functional characterization of BpChr04G00610 under low-temperature stress.

The basic leucine zipper (bZIP) gene, which plays a significant role in the regulation of tolerance to biotic/abiotic stresses, has been characterized in many plant species. Betula platyphylla is a significant afforestation species. To elucidate the stress resistance mechanism of birch, previous studies identified some stress resistance genes. However, the genome-wide identification and characterization of bZIP gene family in the birch have not been reported. Here, the 56 BpbZIP genes were identified and classified into 13 groups in birch. Cis-element analysis showed that the promoters of 56 family genes contained 108 elements, of which 16 were shared by 13 groups. There were 8 pairs of fragment repeats and 1 pair of tandem repeats, indicating that duplication may be the major reason for the amplification of the BpbZIP gene family. Tissue-specific of BpbZIP genes showed 18 genes with the highest expression in roots, 15 in flowers, 11 in xylem and 9 in leaves. In addition, five differentially expressed bZIP genes were identified from the RNA-seq data of birch under low-temperature stress, and the co-expressed differentially expressed genes were further screened. The analysis of gene ontology (GO) enrichment of each co-expression regulatory network showed that they were related to membrane lipids and cell walls. Furthermore, the transient overexpression of BpChr04G00610 decreased the ROS scavenging ability of birch under low-temperature stress, suggesting that it may be more sensitive to low-temperature. In conclusion, this study provides a basis for the study of the function of BpbZIP genes.

Crosstalk between brassinosteroid signaling and variable nutrient environments.

Brassinosteroid (BR) represents a group of steroid hormones that regulate plant growth and development as well as environmental adaptation. The fluctuation of external nutrient elements is a situation that plants frequently face in the natural environment, in which nitrogen (N) and phosphorus (P) are two of the most critical nutrients restraint of the early growth of plants. As the macronutrients, N and P are highly required by plants, but their availability or solubility in the soil is relatively low. Since iron (Fe) and P always modulate each other's content and function in plants mutually antagonistically, the regulatory mechanisms of Fe and P are inextricably linked. Recently, BR has emerged as a critical regulator in nutrient acquisition and phenotypic plasticity in response to the variable nutrient levels in Arabidopsis and rice. Here, we review the current understanding of the crosstalk between BR and the three major nutrients (N, P, and Fe), highlighting how nutrient signaling regulates BR synthesis and signaling to accommodate plant growth and development in Arabidopsis and rice.

The growth-regulating factor PdbGRF1 positively regulates the salt stress response in Populus davidiana × P. bolleana.

Growth-regulating factor (GRF) is a transcription factor unique to plants that plays a crucial role in the growth, development and stress adaptation of plants. However, information on the GRFs related to salt stress in Populus davidiana × P. bolleana is lacking. In this study, we characterized the activity of PdbGRF1 in transgenic Populus davidiana × P. bolleana under salt stress. qRTPCR analyses showed that PdbGRF1 was highly expressed in young leaves and that the pattern of PdbGRF1 expression was significantly changed at most time points under salt stress, which suggests that PdbGRF1 expression may be related to the salt stress response. Moreover, PdbGRF1 overexpression enhanced tolerance to salt stress. A physiological parameter analysis showed that the overexpression of PdbGRF1 significantly decreased the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and increased the activities of antioxidant enzymes (SOD and POD) and the proline content. A molecular analysis showed that PdbGRF1 regulated the expression of PdbPOD17 and PdbAKT1 by binding to the DRE ('A/GCCGAC') in their respective promoters. Together, our results demonstrate that the binding of PdbGRF1 to DRE regulates genes related to stress tolerance and activates the associated physiological pathways, and these effects increase the ROS scavenging ability, reduce the degree of damage to the plasma membrane and ultimately enhance the salt stress response in Populus davidiana × P. bolleana.

Engineered ATG8-binding motif-based selective autophagy to degrade proteins and organelles in planta.

Protein-targeting technologies represent essential approaches in biological research. Protein knockdown tools developed recently in mammalian cells by exploiting natural degradation mechanisms allow for precise determination of protein function and discovery of degrader-type drugs. However, no method to directly target endogenous proteins for degradation is currently available in plants. Here, we describe a novel method for targeted protein clearance by engineering an autophagy receptor with a binder to provide target specificity and an ATG8-binding motif (AIM) to link the targets to nascent autophagosomes, thus harnessing the autophagy machinery for degradation. We demonstrate its specificity and broad potentials by degrading various fluorescence-tagged proteins, including cytosolic mCherry, the nucleus-localized bZIP transcription factor TGA5, and the plasma membrane-anchored brassinosteroid receptor BRI1, as well as fluorescence-coated peroxisomes, using a tobacco-based transient expression system. Stable expression of AIM-based autophagy receptors in Arabidopsis further confirms the feasibility of this approach in selective autophagy of endogenous proteins. With its wide substrate scope and its specificity, our concept of engineered AIM-based selective autophagy could provide a convenient and robust research tool for manipulating endogenous proteins in plants and may open an avenue toward degradation of cytoplasmic components other than proteins in plant research.

The multilayered hierarchical gene regulatory network reveals interaction of transcription factors in response to cadmium in Tamarix hispida roots.

Cadmium (Cd) is a toxic metal that affects the normal growth and development of plants. Roots may directly contact Cd and thus serve as the first barrier in the defense responses of plants. In this study, Tamarix hispida (T. hispida) roots treated with 150 µM CdCl2 were collected for RNA-seq. A total of 2004 differentially expressed genes (DEGs) were identified at different time points. Kyoto Encyclopedia of Genes and Genomes enrichment revealed that the DEGs were significantly enriched in phenylpropanoid biosynthesis, flavonoid biosynthesis and other metabolic pathways. To explore the regulatory role of transcription factors (TFs) involved in the Cd stress response, a multilayer hierarchical gene regulatory network (ML-hGRN) was constructed, including 53 TFs and 54 structural genes in ML-hGRN, with 341 predicted regulatory relationships. Binding of DRE1A, MYC1, FEZ, ERF4 and ERF17 to predicted target genes was detected by ChIP-PCR, and DRE1A, MYC1 and FEZ were transiently overexpressed in T. hispida. The results suggest that these TFs play a key role in the Cd stress response by scavenging reactive oxygen species. In conclusion, this study predicts some Cd-responsive TFs that may have an important function under Cd stress and provides useful information for molecular breeding.

Construction of two regulatory networks related to salt stress and lignocellulosic synthesis under salt stress based on a Populus davidiana × P. bolleana transcriptome analysis.

KEY MESSAGE: Construction of ML-hGRN for the salt pathway in Populus davidiana × P. bolleana. Construction of ML-hGRN for the lignocellulosic pathway in Populus davidiana × P. bolleana under salt stress. Many woody plants, including Populus davidiana × P. bolleana, have made great contributions to human production and life. High salt is one of the main environmental factors that restricts the growth of poplar. This study found that high salt could induce strong biochemical changes in poplar. To detect the effect of salt treatment on gene expression, 18 libraries were sequenced on the Illumina sequencing platform. The results identified a large number of early differentially expressed genes (DEGs) and a small number of late DEGs, which indicated that most of the salt response genes of poplar were early response genes. In addition, 197 TFs, including NAC, ERF, and other TFs related to salt stress, were differentially expressed during salt treatment, which indicated that these TFs may play an important role in the salt stress response of poplar. Based on the RNA-seq analysis results, multilayered hierarchical gene regulatory networks (ML-hGRNs) of salt stress- and lignocellulosic synthesis-related DEGs were constructed using the GGM algorithm. The lignocellulosic synthesis regulatory network under salt stress revealed that lignocellulosic synthesis might play an important role in the process of salt stress resistance. Furthermore, the NAC family transcription factor PdbNAC83, which was found in the upper layer in both pathways, was selected to verify the accuracy of the ML-hGRNs. DAP-seq showed that the binding site of PdbNAC83 included a "TT(G/A)C(G/T)T" motif, and ChIP-PCR further verified that PdbNAC83 can regulate the promoters of at least six predicted downstream genes (PdbNLP2-2, PdbZFP6, PdbMYB73, PdbC2H2-like, PdbMYB93-1, PdbbHLH094) by binding to the "TT(G/A)C(G/T)T" motif, which indicates that the predicted regulatory network diagram obtained in this study is relatively accurate. In conclusion, a species-specific salt response pathway might exist in poplar, and this finding lays a foundation for further study of the regulatory mechanism of the salt stress response and provides new clues for the use of genetic engineering methods to create high-quality and highly resistant forest germplasms.

ATG8-Interacting Motif: Evolution and Function in Selective Autophagy of Targeting Biological Processes.

Autophagy is an evolutionarily conserved vacuolar process functioning in the degradation of cellular components for reuse. In plants, autophagy is generally activated upon stress and its regulation is executed by numbers of AuTophaGy-related genes (ATGs), of which the ATG8 plays a dual role in both biogenesis of autophagosomes and recruitment of ATG8-interacting motif (AIM) anchored selective autophagy receptors (SARs). Such motif is either termed as AIM or ubiquitin-interacting motif (UIM), corresponding to the LC3-interacting region (LIR)/AIM docking site (LDS) or the UIM docking site (UDS) of ATG8, respectively. To date, dozens of AIM or UIM containing SARs have been characterized. However, the knowledge of these motifs is still obscured. In this review, we intend to summarize the current understanding of SAR proteins and discuss the conservation and diversification of the AIMs/UIMs, expectantly providing new insights into the evolution of them in various biological processes in plants.

Harmony but Not Uniformity: Role of Strigolactone in Plants.

Strigolactones (SLs) represent an important new plant hormone class marked by their multifunctional roles in plants and rhizosphere interactions, which stimulate hyphal branching in arbuscular mycorrhizal fungi (AMF) and seed germination of root parasitic plants. SLs have been broadly implicated in regulating root growth, shoot architecture, leaf senescence, nodulation, and legume-symbionts interaction, as well as a response to various external stimuli, such as abiotic and biotic stresses. These functional properties of SLs enable the genetic engineering of crop plants to improve crop yield and productivity. In this review, the conservation and divergence of SL pathways and its biological processes in multiple plant species have been extensively discussed with a particular emphasis on its interactions with other different phytohormones. These interactions may shed further light on the regulatory networks underlying plant growth, development, and stress responses, ultimately providing certain strategies for promoting crop yield and productivity with the challenges of global climate and environmental changes.

Conserved and Diversified Mechanism of Autophagy between Plants and Animals upon Various Stresses.

Autophagy is a highly conserved degradation mechanism in eukaryotes, executing the breakdown of unwanted cell components and subsequent recycling of cellular material for stress relief through vacuole-dependence in plants and yeast while it is lysosome-dependent in animal manner. Upon stress, different types of autophagy are stimulated to operate certain biological processes by employing specific selective autophagy receptors (SARs), which hijack the cargo proteins or organelles to the autophagy machinery for subsequent destruction in the vacuole/lysosome. Despite recent advances in autophagy, the conserved and diversified mechanism of autophagy in response to various stresses between plants and animals still remain a mystery. In this review, we intend to summarize and discuss the characterization of the SARs and their corresponding processes, expectantly advancing the scope and perspective of the evolutionary fate of autophagy between plants and animals.

Chromosome-level reference genome assembly provides insights into aroma biosynthesis in passion fruit (Passiflora edulis).

Passion fruit, native to tropical America, is an agriculturally, economically and ornamentally important fruit plant that is well known for its acid pulp, rich aroma and distinctive flavour. Here, we present a chromosome-level genome assembly of passion fruit by incorporating PacBio long HiFi reads and Hi-C technology. The assembled reference genome is 1.28 Gb size with a scaffold N50 of 126.4 Mb and 99.22% sequences anchored onto nine pseudochromosomes. This genome is highly repetitive, accounting for 86.61% of the assembled genome. A total of 39,309 protein-coding genes were predicted with 93.48% of those being functionally annotated in the public databases. Genome evolution analysis revealed a core eudicot-common γ whole-genome triplication event and a more recent whole-genome duplication event, possibly contributing to the expansion of certain gene families. The 33 rapidly expanded gene families were significantly enriched in the pathways of isoflavone biosynthesis, galactose metabolism, diterpene biosynthesis and fatty acid metabolism, which might be responsible for the formation of featured flavours in the passion fruit. Transcriptome analysis revealed that genes related to ester and ethylene biosynthesis were significantly upregulated in the mature fruit and the expression levels of those genes were consistent with the accumulation of volatile lipid compounds. The passion fruit genome analysis improves our understanding of the genome evolution of this species and sheds new lights into the molecular mechanism of aroma biosynthesis in passion fruit.

Alternative splicing of DSP1 enhances snRNA accumulation by promoting transcription termination and recycle of the processing complex.

Small nuclear RNAs (snRNAs) are the basal components of the spliceosome and play crucial roles in splicing. Their biogenesis is spatiotemporally regulated. However, related mechanisms are still poorly understood. Defective in snRNA processing (DSP1) is an essential component of the DSP1 complex that catalyzes plant snRNA 3'-end maturation by cotranscriptional endonucleolytic cleavage of the primary snRNA transcripts (presnRNAs). Here, we show that DSP1 is subjected to alternative splicing in pollens and embryos, resulting in two splicing variants, DSP1α and DSP1ß. Unlike DSP1α, DSP1ß is not required for presnRNA 3'-end cleavage. Rather, it competes with DSP1α for the interaction with CPSF73-I, the catalytic subunit of the DSP1 complex, which promotes efficient release of CPSF73-I and the DNA-dependent RNA polymerease II (Pol II) from the 3' end of snRNA loci thereby facilitates snRNA transcription termination, resulting in increased snRNA levels in pollens. Taken together, this study uncovers a mechanism that spatially regulates snRNA accumulation.