Extensive sampling of Saccharomyces cerevisiae in Taiwan reveals ecology and evolution of predomesticated lineages.

The ecology and genetic diversity of the model yeast Saccharomyces cerevisiae before human domestication remain poorly understood. Taiwan is regarded as part of this yeast's geographic birthplace, where the most divergent natural lineage was discovered. Here, we extensively sampled the broadleaf forests across this continental island to probe the ancestral species' diversity. We found that S. cerevisiae is distributed ubiquitously at low abundance in the forests. Whole-genome sequencing of 121 isolates revealed nine distinct lineages that diverged from Asian lineages during the Pleistocene, when a transient continental shelf land bridge connected Taiwan to other major landmasses. Three lineages are endemic to Taiwan and six are widespread in Asia, making this region a focal biodiversity hotspot. Both ancient and recent admixture events were detected between the natural lineages, and a genetic ancestry component associated with isolates from fruits was detected in most admixed isolates. Collectively, Taiwanese isolates harbor genetic diversity comparable to that of the whole Asia continent, and different lineages have coexisted at a fine spatial scale even on the same tree. Patterns of variations within each lineage revealed that S. cerevisiae is highly clonal and predominantly reproduces asexually in nature. We identified different selection patterns shaping the coding sequences of natural lineages and found fewer gene family expansion and contractions that contrast with domesticated lineages. This study establishes that S. cerevisiae has rich natural diversity sheltered from human influences, making it a powerful model system in microbial ecology.

Regulators of early maize leaf development inferred from transcriptomes of laser capture microdissection (LCM)-isolated embryonic leaf cells.

The superior photosynthetic efficiency of C4 leaves over C3 leaves is owing to their unique Kranz anatomy, in which the vein is surrounded by one layer of bundle sheath (BS) cells and one layer of mesophyll (M) cells. Kranz anatomy development starts from three contiguous ground meristem (GM) cells, but its regulators and underlying molecular mechanism are largely unknown. To identify the regulators, we obtained the transcriptomes of 11 maize embryonic leaf cell types from five stages of pre-Kranz cells starting from median GM cells and six stages of pre-M cells starting from undifferentiated cells. Principal component and clustering analyses of transcriptomic data revealed rapid pre-Kranz cell differentiation in the first two stages but slow differentiation in the last three stages, suggesting early Kranz cell fate determination. In contrast, pre-M cells exhibit a more prolonged transcriptional differentiation process. Differential gene expression and coexpression analyses identified gene coexpression modules, one of which included 3 auxin transporter and 18 transcription factor (TF) genes, including known regulators of Kranz anatomy and/or vascular development. In situ hybridization of 11 TF genes validated their expression in early Kranz development. We determined the binding motifs of 15 TFs, predicted TF target gene relationships among the 18 TF and 3 auxin transporter genes, and validated 67 predictions by electrophoresis mobility shift assay. From these data, we constructed a gene regulatory network for Kranz development. Our study sheds light on the regulation of early maize leaf development and provides candidate leaf development regulators for future study.

Dual regulation of cytochrome P450 gene expression by two distinct small RNAs, a novel tasiRNA and miRNA, in Marchantia polymorpha.

The miR390-derived TAS3 trans-acting short-interfering RNAs (tasiRNAs) module represents a conserved RNA silencing pathway in the plant kingdom; however, its characterization in the bryophyte Marchantia polymorpha is limited. This study elucidated that MpDCL4 processes MpTAS3 double-stranded RNA (dsRNA) to generate tasiRNAs, primarily from the 5'- and 3'-ends of dsRNA. Notably, we discovered a novel tasiRNA, tasi78A, can negatively regulate a cytochrome P450 gene, MpCYP78A101. Additionally, tasi78A was abundant in MpAGO1, and transient expression assays underscored the role of tasi78A in repressing MpCYP78A101. A microRNA, miR11700, also regulates MpCYP78A101 expression. This coordinate regulation suggests a role in modulating auxin signaling at apical notches of gemma, influencing the growth and sexual organ development of M. polymorpha and emphasizing the significance of RNA silencing in MpCYP78A101 regulation. However, phylogenetic analysis identified another paralog of the CYP78 family, Mp1g14150, which may have a redundant role with MpCYP78A101, explaining the absence of noticeable morphological changes in loss-of-function plants. Taken together, our findings provide new insights into the combined regulatory roles of miR390/MpTAS3/miR11700 in controlling MpCYP78A101 and expand our knowledge about the biogenesis and regulation of tasiRNAs in M. polymorpha.

Maize Golden2-like transcription factors boost rice chloroplast development, photosynthesis, and grain yield.

Chloroplasts are the sites for photosynthesis, and two Golden2-like factors act as transcriptional activators of chloroplast development in rice (Oryza sativa L.) and maize (Zea mays L.). Rice OsGLK1 and OsGLK2 are orthologous to maize ZmGLK1 (ZmG1) and ZmGLK2 (ZmG2), respectively. However, while rice OsGLK1 and OsGLK2 act redundantly to regulate chloroplast development in mesophyll cells, maize ZmG1 and ZmG2 are functionally specialized and expressed in different cell-specific manners. To boost rice chloroplast development and photosynthesis, we generated transgenic rice plants overexpressing ZmG1 and ZmG2, individually or simultaneously, with constitutive promoters (pZmUbi::ZmG1 and p35S::ZmG2) or maize promoters (pZmG1::ZmG1, pZmG2::ZmG2, and pZmG1::ZmG1/pZmG2::ZmG2). Both ZmG1 and ZmG2 genes were highly expressed in transgenic rice leaves. Moreover, ZmG1 and ZmG2 showed coordinated expression in pZmG1::ZmG1/pZmG2::ZmG2 plants. All Golden2-like (GLK) transgenic plants had higher chlorophyll and protein contents, Rubisco activities and photosynthetic rates per unit leaf area in flag leaves. However, the highest grain yields occurred when maize promoters were used; pZmG1::ZmG1, pZmG2::ZmG2, and pZmG1::ZmG1/pZmG2::ZmG2 transgenic plants showed increases in grain yield by 51%, 47%, and 70%, respectively. In contrast, the pZmUbi::ZmG1 plant produced smaller seeds without yield increases. Transcriptome analysis indicated that maize GLKs act as master regulators promoting the expression of both photosynthesis-related and stress-responsive regulatory genes in both rice shoot and root. Thus, by promoting these important functions under the control of their own promoters, maize GLK1 and GLK2 genes together dramatically improved rice photosynthetic performance and productivity. A similar approach can potentially improve the productivity of many other crops.

Analysis of genomic distributions of SARS-CoV-2 reveals a dominant strain type with strong allelic associations.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal agent of COVID 19, continues to evolve since its first emergence in December 2019. Using the complete sequences of 1,932 SARS-CoV-2 genomes, various clustering analyses consistently identified six types of the strains. Independent of the dendrogram construction, 13 signature variations in the form of single nucleotide variations (SNVs) in protein coding regions and one SNV in the 5' untranslated region (UTR) were identified and provided a direct interpretation for the six types (types I to VI). The six types of the strains and their underlying signature SNVs were validated in two subsequent analyses of 6,228 and 38,248 SARS-CoV-2 genomes which became available later. To date, type VI, characterized by the four signature SNVs C241T (5'UTR), C3037T (nsp3 F924F), C14408T (nsp12 P4715L), and A23403G (Spike D614G), with strong allelic associations, has become the dominant type. Since C241T is in the 5' UTR with uncertain significance and the characteristics can be captured by the other three strongly associated SNVs, we focus on the other three. The increasing frequency of the type VI haplotype 3037T-14408T-23403G in the majority of the submitted samples in various countries suggests a possible fitness gain conferred by the type VI signature SNVs. The fact that strains missing one or two of these signature SNVs fail to persist implies possible interactions among these SNVs. Later SNVs such as G28881A, G28882A, and G28883C have emerged with strong allelic associations, forming new subtypes. This study suggests that SNVs may become an important consideration in SARS-CoV-2 classification and surveillance.

Maize ANT1 modulates vascular development, chloroplast development, photosynthesis, and plant growth.

Arabidopsis AINTEGUMENTA (ANT), an AP2 transcription factor, is known to control plant growth and floral organogenesis. In this study, our transcriptome analysis and in situ hybridization assays of maize embryonic leaves suggested that maize ANT1 (ZmANT1) regulates vascular development. To better understand ANT1 functions, we determined the binding motif of ZmANT1 and then showed that ZmANT1 binds the promoters of millet SCR1, GNC, and AN3, which are key regulators of Kranz anatomy, chloroplast development, and plant growth, respectively. We generated a mutant with a single-codon deletion and two frameshift mutants of the ANT1 ortholog in the C4 millet Setaria viridis by the CRISPR/Cas9 technique. The two frameshift mutants displayed reduced photosynthesis efficiency and growth rate, smaller leaves, and lower grain yields than wild-type (WT) plants. Moreover, their leaves sporadically exhibited distorted Kranz anatomy and vein spacing. Conducting transcriptomic analysis of developing leaves in the WT and the three mutants we identified differentially expressed genes (DEGs) in the two frameshift mutant lines and found many down-regulated DEGs enriched in photosynthesis, heme, tetrapyrrole binding, and antioxidant activity. In addition, we predicted many target genes of ZmANT1 and chose 13 of them to confirm binding of ZmANT1 to their promoters. Based on the above observations, we proposed a model for ANT1 regulation of cell proliferation and leaf growth, vascular and vein development, chloroplast development, and photosynthesis through its target genes. Our study revealed biological roles of ANT1 in several developmental processes beyond its known roles in plant growth and floral organogenesis.

Molecular asymmetry in the cephalochordate embryo revealed by single-blastomere transcriptome profiling.

Studies in various animals have shown that asymmetrically localized maternal transcripts play important roles in axial patterning and cell fate specification in early embryos. However, comprehensive analyses of the maternal transcriptomes with spatial information are scarce and limited to a handful of model organisms. In cephalochordates (amphioxus), an early branching chordate group, maternal transcripts of germline determinants form a compact granule that is inherited by a single blastomere during cleavage stages. Further blastomere separation experiments suggest that other transcripts associated with the granule are likely responsible for organizing the posterior structure in amphioxus; however, the identities of these determinants remain unknown. In this study, we used high-throughput RNA sequencing of separated blastomeres to examine asymmetrically localized transcripts in two-cell and eight-cell stage embryos of the amphioxus Branchiostoma floridae. We identified 111 and 391 differentially enriched transcripts at the 2-cell stage and the 8-cell stage, respectively, and used in situ hybridization to validate the spatial distribution patterns for a subset of these transcripts. The identified transcripts could be categorized into two major groups: (1) vegetal tier/germ granule-enriched and (2) animal tier/anterior-enriched transcripts. Using zebrafish as a surrogate model system, we showed that overexpression of one animal tier/anterior-localized amphioxus transcript, zfp665, causes a dorsalization/anteriorization phenotype in zebrafish embryos by downregulating the expression of the ventral gene, eve1, suggesting a potential function of zfp665 in early axial patterning. Our results provide a global transcriptomic blueprint for early-stage amphioxus embryos. This dataset represents a rich platform to guide future characterization of molecular players in early amphioxus development and to elucidate conservation and divergence of developmental programs during chordate evolution.

Behavioral and brain- transcriptomic synchronization between the two opponents of a fighting pair of the fish Betta splendens.

Conspecific male animals fight for resources such as food and mating opportunities but typically stop fighting after assessing their relative fighting abilities to avoid serious injuries. Physiologically, how the fighting behavior is controlled remains unknown. Using the fighting fish Betta splendens, we studied behavioral and brain-transcriptomic changes during the fight between the two opponents. At the behavioral level, surface-breathing, and biting/striking occurred only during intervals between mouth-locking. Eventually, the behaviors of the two opponents became synchronized, with each pair showing a unique behavioral pattern. At the physiological level, we examined the expression patterns of 23,306 brain transcripts using RNA-sequencing data from brains of fighting pairs after a 20-min (D20) and a 60-min (D60) fight. The two opponents in each D60 fighting pair showed a strong gene expression correlation, whereas those in D20 fighting pairs showed a weak correlation. Moreover, each fighting pair in the D60 group showed pair-specific gene expression patterns in a grade of membership analysis (GoM) and were grouped as a pair in the heatmap clustering. The observed pair-specific individualization in brain-transcriptomic synchronization (PIBS) suggested that this synchronization provides a physiological basis for the behavioral synchronization. An analysis using the synchronized genes in fighting pairs of the D60 group found genes enriched for ion transport, synaptic function, and learning and memory. Brain-transcriptomic synchronization could be a general phenomenon and may provide a new cornerstone with which to investigate coordinating and sustaining social interactions between two interacting partners of vertebrates.

Whole-Genome Duplication Facilitated the Evolution of C4 Photosynthesis in Gynandropsis gynandra.

In higher plants, whole-genome duplication (WGD) is thought to facilitate the evolution of C4 photosynthesis from C3 photosynthesis. To understand this issue, we used new and existing leaf-development transcriptomes to construct two coding sequence databases for C4Gynandropsis gynandra and C3Tarenaya hassleriana, which shared a WGD before their divergence. We compared duplicated genes in the two species and found that the WGD contributed to four aspects of the evolution of C4 photosynthesis in G. gynandra. First, G. gynandra has retained the duplicates of ALAAT (alanine aminotransferase) and GOGAT (glutamine oxoglutarate aminotransferase) for nitrogen recycling to establish a photorespiratory CO2 pump in bundle sheath (BS) cells for increasing photosynthesis efficiency, suggesting that G. gynandra experienced a C3-C4 intermediate stage during the C4 evolution. Second, G. gynandra has retained almost all known vein-development-related paralogous genes derived from the WGD event, likely contributing to the high vein complexity of G. gynandra. Third, the WGD facilitated the evolution of C4 enzyme genes and their recruitment into the C4 pathway. Fourth, several genes encoding photosystem I proteins were derived from the WGD and are upregulated in G. gynandra, likely enabling the NADH dehydrogenase-like complex to produce extra ATPs for the C4 CO2 concentration mechanism. Thus, the WGD apparently played an enabler role in the evolution of C4 photosynthesis in G. gynandra. Importantly, an ALAAT duplicate became highly expressed in BS cells in G. gynandra, facilitating nitrogen recycling and transition to the C4 cycle. This study revealed how WDG may facilitate C4 photosynthesis evolution.

Comparative transcriptomics method to infer gene coexpression networks and its applications to maize and rice leaf transcriptomes.

Time-series transcriptomes of a biological process obtained under different conditions are useful for identifying the regulators of the process and their regulatory networks. However, such data are 3D (gene expression, time, and condition), and there is currently no method that can deal with their full complexity. Here, we developed a method that avoids time-point alignment and normalization between conditions. We applied it to analyze time-series transcriptomes of developing maize leaves under light-dark cycles and under total darkness and obtained eight time-ordered gene coexpression networks (TO-GCNs), which can be used to predict upstream regulators of any genes in the GCNs. One of the eight TO-GCNs is light-independent and likely includes all genes involved in the development of Kranz anatomy, which is a structure crucial for the high efficiency of photosynthesis in C4 plants. Using this TO-GCN, we predicted and experimentally validated a regulatory cascade upstream of SHORTROOT1, a key Kranz anatomy regulator. Moreover, we applied the method to compare transcriptomes from maize and rice leaf segments and identified regulators of maize C4 enzyme genes and RUBISCO SMALL SUBUNIT2 Our study provides not only a powerful method but also novel insights into the regulatory networks underlying Kranz anatomy development and C4 photosynthesis.

Chromosomal-level genome assembly of the semi-dwarf rice Taichung Native 1, an initiator of Green Revolution.

Here we report the 409.5 Mb chromosome-level assembly of the first bred semi-dwarf rice, the Taichung Native 1 (TN1), which served as the template for the development of the Green Revolution (GR) cultivar IR8 "miracle rice". We sequenced the TN1 genome utilizing multiple platforms and produced PacBio long reads, Illumina paired-end reads, Illumina mate-pair reads and 10x Genomics linked reads. We used a hybrid approach to assemble the 226× coverage of sequences by a combination of de novo and reference-guided approaches. The assembled TN1 genome has an N50 scaffold size of 33.1 Mb with the longest measuring 45.5 Mb. We annotated 37,526 genes, in which 24,102 (64.23%) were assigned Blast2GO annotations. The genome has 4672 or 95.4% complete BUSCOs and a repeat content of 51.52%. We developed our own method of creating a GR pangenome using the orthologous relationships of the proteins of TN1, IR8, MH63 and IR64, identifying 16,999 core orthologue groups of Green Revolution. From the pangenome, we identified a set of shared and unique gene ontology terms for the accessory clusters, characterizing TN1, IR8, MH63 and IR64. This TN1 genome assembly and GR pangenome will be a resource for new genomic discoveries about Green Revolution, and for improving the disease and insect resistances and the yield of rice.

Generation of TRIM28 Knockout K562 Cells by CRISPR/Cas9 Genome Editing and Characterization of TRIM28-Regulated Gene Expression in Cell Proliferation and Hemoglobin Beta Subunits.

TRIM28 is a scaffold protein that interacts with DNA-binding proteins and recruits corepressor complexes to cause gene silencing. TRIM28 contributes to physiological functions such as cell growth and differentiation. In the chronic myeloid leukemia cell line K562, we edited TRIM28 using CRISPR/Cas9 technology, and the complete and partial knockout (KO) cell clones were obtained and confirmed using quantitative droplet digital PCR (ddPCR) technology. The amplicon sequencing demonstrated no off-target effects in our gene editing experiments. The TRIM28 KO cells grew slowly and appeared red, seeming to have a tendency towards erythroid differentiation. To understand how TRIM28 controls K562 cell proliferation and differentiation, transcriptome profiling analysis was performed in wild-type and KO cells to identify TRIM28-regulated genes. Some of the RNAs that encode the proteins regulating the cell cycle were increased (such as p21) or decreased (such as cyclin D2) in TRIM28 KO cell clones; a tumor marker, the MAGE (melanoma antigen) family, which is involved in cell proliferation was reduced. Moreover, we found that knockout of TRIM28 can induce miR-874 expression to downregulate MAGEC2 mRNA via post-transcriptional regulation. The embryonic epsilon-globin gene was significantly increased in TRIM28 KO cell clones through the downregulation of transcription repressor SOX6. Taken together, we provide evidence to demonstrate the regulatory network of TRIM28-mediated cell growth and erythroid differentiation in K562 leukemia cells.

Whole-Genome Sequence Resource of Calonectria ilicicola, the Casual Pathogen of Soybean Red Crown Rot.

Calonectria ilicicola (anamorph: Cylindrocladium parasiticum) is a soilborne plant-pathogenic fungus with a broad host range, and it can cause red crown rot of soybean and Cylindrocladium black rot of peanut, which has become an emerging threat to crop production worldwide. Limited molecular studies have focused on Calonectria ilicicola and one of the possible difficulties is the lack of genomic resources. This study presents the first high quality and near-completed genome of C. ilicicola, using the Oxford Nanopore GridION sequencing platform. A total of 16 contigs were assembled and the genome of C. ilicicola isolate F018 was estimated to have 11 chromosomes. Currently, the C. ilicicola F018 genome represents the most contiguous assembly, which has the lowest contig number and the highest contig N50 among all Calonectria genome resources. Putative protein-coding sequences and secretory proteins were estimated to be 17,308 and 1,930 in the C. ilicicola F018 genome, respectively; and the prediction was close to other plant-pathogenic fungi, such as Fusarium species, within the Nectriaceae family. The availability of this high-quality genome resource is expected to facilitate research on fungal biology and genetics of C. ilicicola and to support advanced understanding of pathogen virulence and disease management.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Blast Fungal Genomes Show Frequent Chromosomal Changes, Gene Gains and Losses, and Effector Gene Turnover.

Pyricularia is a fungal genus comprising several pathogenic species causing the blast disease in monocots. Pyricularia oryzae, the best-known species, infects rice, wheat, finger millet, and other crops. As past comparative and population genomics studies mainly focused on isolates of P. oryzae, the genomes of the other Pyricularia species have not been well explored. In this study, we obtained a chromosomal-level genome assembly of the finger millet isolate P. oryzae MZ5-1-6 and also highly contiguous assemblies of Pyricularia sp. LS, P. grisea, and P. pennisetigena. The differences in the genomic content of repetitive DNA sequences could largely explain the variation in genome size among these new genomes. Moreover, we found extensive gene gains and losses and structural changes among Pyricularia genomes, including a large interchromosomal translocation. We searched for homologs of known blast effectors across fungal taxa and found that most avirulence effectors are specific to Pyricularia, whereas many other effectors share homologs with distant fungal taxa. In particular, we discovered a novel effector family with metalloprotease activity, distinct from the well-known AVR-Pita family. We predicted 751 gene families containing putative effectors in 7 Pyricularia genomes and found that 60 of them showed differential expression in the P. oryzae MZ5-1-6 transcriptomes obtained under experimental conditions mimicking the pathogen infection process. In summary, this study increased our understanding of the structural, functional, and evolutionary genomics of the blast pathogen and identified new potential effector genes, providing useful data for developing crops with durable resistance.

Co-opting sulphur-carrier proteins from primary metabolic pathways for 2-thiosugar biosynthesis.

Sulphur is an essential element for life and is ubiquitous in living systems. Yet how the sulphur atom is incorporated into many sulphur-containing secondary metabolites is poorly understood. For bond formation between carbon and sulphur in primary metabolites, the major ionic sulphur sources are the persulphide and thiocarboxylate groups on sulphur-carrier (donor) proteins. Each group is post-translationally generated through the action of a specific activating enzyme. In all reported bacterial cases, the gene encoding the enzyme that catalyses the carbon-sulphur bond formation reaction and that encoding the cognate sulphur-carrier protein exist in the same gene cluster. To study the production of the 2-thiosugar moiety in BE-7585A, an antibiotic from Amycolatopsis orientalis, we identified a putative 2-thioglucose synthase, BexX, whose protein sequence and mode of action seem similar to those of ThiG, the enzyme that catalyses thiazole formation in thiamine biosynthesis. However, no gene encoding a sulphur-carrier protein could be located in the BE-7585A cluster. Subsequent genome sequencing uncovered a few genes encoding sulphur-carrier proteins that are probably involved in the biosynthesis of primary metabolites but only one activating enzyme gene in the A. orientalis genome. Further experiments showed that this activating enzyme can adenylate each of these sulphur-carrier proteins and probably also catalyses the subsequent thiolation, through its rhodanese domain. A proper combination of these sulphur-delivery systems is effective for BexX-catalysed 2-thioglucose production. The ability of BexX to selectively distinguish sulphur-carrier proteins is given a structural basis using X-ray crystallography. This study is, to our knowledge, the first complete characterization of thiosugar formation in nature and also demonstrates the receptor promiscuity of the A. orientalis sulphur-delivery system. Our results also show that co-opting the sulphur-delivery machinery of primary metabolism for the biosynthesis of sulphur-containing natural products is probably a general strategy found in nature.

Integrative transcriptome sequencing reveals extensive alternative trans-splicing and cis-backsplicing in human cells.

Transcriptionally non-co-linear (NCL) transcripts can originate from trans-splicing (trans-spliced RNA; 'tsRNA') or cis-backsplicing (circular RNA; 'circRNA'). While numerous circRNAs have been detected in various species, tsRNAs remain largely uninvestigated. Here, we utilize integrative transcriptome sequencing of poly(A)- and non-poly(A)-selected RNA-seq data from diverse human cell lines to distinguish between tsRNAs and circRNAs. We identified 24,498 NCL events and found that a considerable proportion (20-35%) of them arise from both tsRNAs and circRNAs, representing extensive alternative trans-splicing and cis-backsplicing in human cells. We show that sequence generalities of exon circularization are also observed in tsRNAs. Recapitulation of NCL RNAs further shows that inverted Alu repeats can simultaneously promote the formation of tsRNAs and circRNAs. However, tsRNAs and circRNAs exhibit quite different, or even opposite, expression patterns, in terms of correlation with the expression of their co-linear counterparts, expression breadth/abundance, transcript stability, and subcellular localization preference. These results indicate that tsRNAs and circRNAs may play different regulatory roles and analysis of NCL events should take the joint effects of different NCL-splicing types and joint effects of multiple NCL events into consideration. This study describes the first transcriptome-wide analysis of trans-splicing and cis-backsplicing, expanding our understanding of the complexity of the human transcriptome.

Elevated auxin biosynthesis and transport underlie high vein density in C4 leaves.

High vein density, a distinctive trait of C4 leaves, is central to both C3-to-C4 evolution and conversion of C3 to C4-like crops. We tested the hypothesis that high vein density in C4 leaves is due to elevated auxin biosynthesis and transport in developing leaves. Up-regulation of genes in auxin biosynthesis pathways and higher auxin content were found in developing C4 leaves compared with developing C3 leaves. The same observation held for maize foliar (C4) and husk (C3) leaf primordia. Moreover, auxin content and vein density were increased in loss-of-function mutants of Arabidopsis MYC2, a suppressor of auxin biosynthesis. Treatment with an auxin biosynthesis inhibitor or an auxin transport inhibitor led to much fewer veins in new leaves. Finally, both Arabidopsis thaliana auxin efflux transporter pin1 and influx transporter lax2 mutants showed reduced vein numbers. Thus, development of high leaf vein density requires elevated auxin biosynthesis and transport.

Experimental Evolution of Yeast for High-Temperature Tolerance.

Thermotolerance is a polygenic trait that contributes to cell survival and growth under unusually high temperatures. Although some genes associated with high-temperature growth (Htg+) have been identified, how cells accumulate mutations to achieve prolonged thermotolerance is still mysterious. Here, we conducted experimental evolution of a Saccharomyces cerevisiae laboratory strain with stepwise temperature increases for it to grow at 42 °C. Whole genome resequencing of 14 evolved strains and the parental strain revealed a total of 153 mutations in the evolved strains, including single nucleotide variants, small INDELs, and segmental duplication/deletion events. Some mutations persisted from an intermediate temperature to 42 °C, so they might be Htg+ mutations. Functional categorization of mutations revealed enrichment of exonic mutations in the SWI/SNF complex and F-type ATPase, pointing to their involvement in high-temperature tolerance. In addition, multiple mutations were found in a general stress-associated signal transduction network consisting of Hog1 mediated pathway, RAS-cAMP pathway, and Rho1-Pkc1 mediated cell wall integrity pathway, implying that cells can achieve Htg+ partly through modifying existing stress regulatory mechanisms. Using pooled segregant analysis of five Htg+ phenotype-orientated pools, we inferred causative mutations for growth at 42 °C and identified those mutations with stronger impacts on the phenotype. Finally, we experimentally validated a number of the candidate Htg+ mutations. This study increased our understanding of the genetic basis of yeast tolerance to high temperature.

The SnRK1-eIFiso4G1 signaling relay regulates the translation of specific mRNAs in Arabidopsis under submergence.

Cellular responses to oxygen deprivation are essential for survival during energy crises in plants and animals. Hypoxia caused by submergence results in reprogramming of translation dynamic in plants, but the molecular mechanisms are not well understood. Here we show that Arabidopsis Snf1-related protein kinase 1 (SnRK1) phosphorylates the translation initiation factor eIFiso4G to regulate translation dynamic under submergence. In Arabidopsis, there are two eIFiso4G genes, eIFiso4G1 and eIFiso4G2, which belong to the eIF4G family. Both eIFiso4Gs were phosphorylated by SnRK1 under submergence. Interestingly, the eIFiso4G1 knockout mutant, but not the eIFiso4G2 mutant, became more sensitive to submergence, implying that eIFiso4G1 is involved in regulating submergence tolerance in Arabidopsis. Comparison of RNA sequences in the polysome fraction and the RNAs immunoprecipitated by eIFiso4G1 from Col-0 and the SnRK1 and eIFiso4G1 mutants revealed that lack of eIFiso4G1 phosphorylation disrupts the translation of specific mRNAs under submergence. Taken together, our findings suggest that the SnRK1-eIFiso4G1 relay controls the translation of an array of genes under hypoxia, including core hypoxia response genes and genes related to stress response and biosynthetic process.