Disruption of the bHLH transcription factor Abnormal Tapetum 1 causes male sterility in watermelon

Although male sterility has been identified as a useful trait for hybrid vigor utilization and hybrid seed production,its underlying molecular mechanisms in Cucurbitaceae species are still largely unclear.Here,a spontaneous male-sterile watermelon mutant,Se18,was reported to have abnormal tapetum development,which resulted in completely aborted pollen grains.Map-based cloning demonstrated that the causal gene Citrullus lanatus Abnormal Tapetum 1(ClATM1)encodes a basic helix-loop-helix(bHLH)transcription factor with a 10-bp deletion and produces a truncated protein without the bHLH interaction and functional(BIF)domain in Se18 plants.qRT–PCR and RNA in situ hybridization showed that ClATM1 is specifically expressed in the tapetum layer and in microsporocytes during stages 6–8a of anther development.The genetic function of ClATM1 in regulating anther development was verified by CRISPR/Cas9-mediated mutagenesis.Moreover,ClATM1 was significantly downregulated in the Se18 mutant,displaying a clear dose effect at the transcriptional level.Subsequent dual-luciferase reporter,β-glucuronidase(GUS)activity,and yeast one-hybrid assays indicated that ClATM1 could activate its own transcriptional expression through promoter binding.Collectively,ClATM1 is the first male sterility gene cloned from watermelon,and its self-regulatory activity provides new insights into the molecular mechanism underlying anther development in plants.

The Corylus mandshurica genome provides insights into the evolution of Betulaceae genomes and hazelnut breeding

Hazelnut is popular for its flavor,and it has also been suggested that hazelnut is beneficial to cardiovascular health because it is rich in oleic acid.Here,we report the first high-quality chromosome-scale genome for the hazelnut species Corylus mandshurica(2n=22),which has a high concentration of oleic acid in its nuts.The assembled genome is 367.67Mb in length,and the contig N50 is 14.85 Mb.All contigs were assembled into 11 chromosomes,and 28,409 protein-coding genes were annotated.We reconstructed the evolutionary trajectories of the genomes of Betulaceae species and revealed that the 11 chromosomes of the hazelnut genus were derived from the most ancestral karyotype in Betula pendula,which has 14 protochromosomes,by inferring homology among five Betulaceae genomes.We identified 96 candidate genes involved in oleic acid biosynthesis,and 10 showed rapid evolution or positive selection.These findings will help us to understand the mechanisms of lipid synthesis and storage in hazelnuts.Several gene families related to salicylic acid metabolism and stress responses experienced rapid expansion in this hazelnut species,which may have increased its stress tolerance.The reference genome presented here constitutes a valuable resource for molecular breeding and genetic improvement of the important agronomic properties of hazelnut.

A point mutation resulting in a 13 bp deletion in the coding sequence of Cldf leads to a GA-deficient dwarf phenotype in watermelon

The dwarf architecture is an important and valuable agronomic trait in watermelon breeding and has the potential to increase fruit yield and reduce labor cost in crop cultivation.However,the molecular basis for dwarfism in watermelon remains largely unknown.In this study,a recessive dwarf allele(designated as Cldf(Citrullus lanatus dwarfism))was fine mapped in a 32.88 kb region on chromosome 09 using F2 segregation populations derived from reciprocal crossing of a normal line M08 and a dwarf line N21.Gene annotation of the corresponding region revealed that the Cla015407 gene encoding a gibberellin 3β-hydroxylase functions as the best possible candidate gene for Cldf.Sequence analysis showed that the fourth polymorphism site(a G to A point mutation)at the 3′AG splice receptor site of the intron leads to a 13 bp deletion in the coding sequence of Cldf in dwarf line N21 and thus results in a truncated protein lacking the conserved domain for binding 2-oxoglutarate.In addition,the dwarf phenotype of Cldf could be rescued by exogenous GA3 application.Phylogenetic analysis suggested that the small multigene family GA3ox(GA3 oxidase)in cucurbit species may originate from three ancient lineages in Cucurbitaceae.All these data support the conclusion that Cldf is a GA-deficient mutant,which together with the cosegregated marker can be used for breeding new dwarf cultivars.

Methyl jasmonate mediates melatonin-induced cold tolerance of grafted watermelon plants

Root–shoot communication has a critical role in plant adaptation to environmental stress.Grafting is widely applied to enhance the abiotic stress tolerance of many horticultural crop species;however,the signal transduction mechanism involved in this tolerance remains unknown.Here,we show that pumpkin-or figleaf gourd rootstock-enhanced cold tolerance of watermelon shoots is accompanied by increases in the accumulation of melatonin,methyl jasmonate(MeJA),and hydrogen peroxide(H_(2)O_(2)).Increased melatonin levels in leaves were associated with both increased melatonin in rootstocks and MeJA-induced melatonin biosynthesis in leaves of plants under cold stress.Exogenous melatonin increased the accumulation of MeJA and H_(2)O_(2) and enhanced cold tolerance,while inhibition of melatonin accumulation attenuated rootstock-induced MeJA and H_(2)O_(2) accumulation and cold tolerance.MeJA application induced H_(2)O_(2) accumulation and cold tolerance,but inhibition of JA biosynthesis abolished rootstock-or melatonin-induced H_(2)O_(2) accumulation and cold tolerance.Additionally,inhibition of H_(2)O_(2) production attenuated MeJA-induced tolerance to cold stress.Taken together,our results suggest that melatonin is involved in grafting-induced cold tolerance by inducing the accumulation of MeJA and H_(2)O_(2).MeJA subsequently increases melatonin accumulation,forming a self-amplifying feedback loop that leads to increased H_(2)O_(2) accumulation and cold tolerance.This study reveals a novel regulatory mechanism of rootstock-induced cold tolerance.

The role of watermelon caffeic acid O-methyltransferase (ClCOMT1) in melatonin biosynthesis and abiotic stress tolerance

Melatonin is a pleiotropic signaling molecule that regulates plant growth and responses to various abiotic stresses.The last step of melatonin synthesis in plants can be catalyzed by caffeic acid O-methyltransferase(COMT),a multifunctional enzyme reported to have N-acetylserotonin O-methyltransferase(ASMT)activity;however,the ASMT activity of COMT has not yet been characterized in nonmodel plants such as watermelon(Citrullus lanatus).Here,a total of 16 putative O-methyltransferase(ClOMT)genes were identified in watermelon.Among them,ClOMT03(Cla97C07G144540)was considered a potential COMT gene(renamed ClCOMT1)based on its high identities(60.00–74.93%)to known COMT genes involved in melatonin biosynthesis,expression in almost all tissues,and upregulation under abiotic stresses.The ClCOMT1 protein was localized in the cytoplasm.Overexpression of ClCOMT1 significantly increased melatonin contents,while ClCOMT1 knockout using the CRISPR/Cas-9 system decreased melatonin contents in watermelon calli.These results suggest that ClCOMT1 plays an essential role in melatonin biosynthesis in watermelon.In addition,ClCOMT1 expression in watermelon was upregulated by cold,drought,and salt stress,accompanied by increases in melatonin contents.Overexpression of ClCOMT1 enhanced transgenic Arabidopsis tolerance against such abiotic stresses,indicating that ClCOMT1 is a positive regulator of plant tolerance to abiotic stresses.

Genome-scale angiosperm phylogenies based on nuclear,plastome,and mitochondrial datasets

Angiosperms dominate the Earth’s ecosystems and provide most of the basic necessities for human life.The major angiosperm clades comprise 64 orders,as recognized by the APGⅣclassification.However,the phylogenetic relationships of angiosperms remain unclear,as phylogenetic trees with different topologies have been reconstructed depending on the sequence datasets utilized,from targeted genes to transcriptomes.Here,we used currently available de novo genome data to reconstruct the phylogenies of 366 angiosperm species from 241 genera belonging to 97 families across 43 of the 64 orders based on orthologous genes from the nuclear,plastid,and mitochondrial genomes of the same species with compatible datasets.The phylogenetic relationships were largely consistent with previously constructed phylogenies based on sequence variations in each genome type.However,there were major inconsistencies in the phylogenetic relationships of the five Mesangiospermae lineages when different genomes were examined.We discuss ways to address these inconsistencies,which could ultimately lead to the reconstruction of a comprehensive angiosperm tree of life.The angiosperm phylogenies presented here provide a basic framework for further updates and comparisons.These phylogenies can also be used as guides to examine the evolutionary trajectories among the three genome types during lineage radiation.

Optimization of digital multi-beamforming for space-based ADS-B using distributed cooperative coevolution with an adaptive grouping strategy

Space-based Automatic Dependent Surveillance-Broadcast(ADS-B)technology can eliminate the blind spots of terrestrial ADS-B systems because of its global coverage capability.However,the space-based ADS-B system faces new problems such as extremely low Signal-toNoise Ratio(SNR)and serious co-channel interference,which result in long update intervals.To minimize the position message update interval at an update probability of 95%with full coverage constraint,this paper presents an optimization model of digital multi-beamforming for space-based ADS-B.Then,a coevolution method DECCG_A&A is proposed to enhance the optimization efficiency by using an improved adaptive grouping strategy.The strategy is based on the locations of uncovered areas and the aircraft density under the coverage of each beam.Simulation results show that the update interval can be effectively controlled to be below 8 seconds compared with other existing methods,and DECCG_A&A is superior in convergence to the Genetic Algorithm(GA)as well as the coevolution algorithms using other grouping strategies.Overall,the proposed optimization model and method can significantly reduce the update interval,thus improving the surveillance performance of space-based ADS-B for air traffic control.