Strong Cold Tolerance Research Articles

How to alleviate seasonal limitations on water quality in farmland ditches? The importance of plant selection and configuration

In subtropical monsoon climate regions, traditional plants in constructed wetlands such as farmland ditches underperform in cold months, detracting from both purification capacity and esthetic appeal. To alleviate this weakness, this study introduced Phalaris arundinacea, a species with strong adaptability and cold tolerance, into a plant community dominated by Phragmites australis, constructing an ingenious composite plant community for year‐round water quality restoration and enhancement of attractiveness. First, laboratory simulations revealed significant seasonal differences in the removal rates of ammonia nitrogen (NH3‐N), total nitrogen (TN), and total phosphorus (TP) by the P. arundinacea community and P. australis community under different pollutant loads. Phragmites australis showed superior NH3‐N and TN removal capabilities from May to October, whereas P. arundinacea excelled in the rest of the months throughout the year. For TP removal, P. australis outperformed P. arundinacea from July to October, while P. arundinacea was more effective from January to May. We then verified this in rear farmland ditches, where P. australis were strategically partial substituted with P. arundinacea (Partial Replacement Treatment [PRT]), and compared it with unchanged farmland ditches (Control Treatment). We found that PRT enhanced decontamination efficiency over the year, especially significantly improving the water quality during colder months. Hence, this study advocates a novel strategy for effective annual decontamination and maintenance of wetlands such as farmland ditches, highlighting the importance of seasonally adaptive plant communities for water restoration. This transformative approach dramatically advances the field of wetland management, insisting on the important role of cold‐resistant species for year‐round ecosystem service optimization.

Integration of molecular breeding and multi-resistance screening for developing a promising restorer line Guihui5501 with heavy grain, good grain quality, and endurance to biotic and abiotic stresses.

Rice, a critical staple on a global scale, faces escalating challenges in yield preservation due to the rising prevalence of abiotic and biotic stressors, exacerbated by frequent climatic fluctuations in recent years. Moreover, the scorching climate prevalent in the rice-growing regions of South China poses obstacles to the cultivation of good-quality, heavy-grain varieties. Addressing this dilemma requires the development of resilient varieties capable of withstanding multiple stress factors. To achieve this objective, our study employed the broad-spectrum blast-resistant line Digu, the brown planthopper (BPH)-resistant line ASD7, and the heavy-grain backbone restorer lines Fuhui838 (FH838) and Shuhui527 (SH527) as parental materials for hybridization and multiple crossings. The incorporation of molecular markers facilitated the rapid pyramiding of six target genes (Pi5, Pita, Pid2, Pid3, Bph2, and Wxb ). Through a comprehensive evaluation encompassing blast resistance, BPH resistance, cold tolerance, grain appearance, and quality, alongside agronomic trait selection, a promising restorer line, Guihui5501 (GH5501), was successfully developed. It demonstrated broad-spectrum resistance to blast, exhibiting a resistance frequency of 77.33% against 75 artificially inoculated isolates, moderate resistance to BPH (3.78 grade), strong cold tolerance during the seedling stage (1.80 grade), and characteristics of heavy grains (1,000-grain weight reaching 35.64 g) with good grain quality. The primary rice quality parameters for GH5501, with the exception of alkali spreading value, either met or exceeded the second-grade national standard for premium edible rice varieties, signifying a significant advancement in the production of good-quality heavy-grain varieties in the southern rice-growing regions. Utilizing GH5501, a hybrid combination named Nayou5501, characterized by high yield, good quality, and resistance to multiple stresses, was bred and received approval as a rice variety in Guangxi in 2021. Furthermore, genomic analysis with gene chips revealed that GH5501 possessed an additional 20 exceptional alleles, such as NRT1.1B for efficient nitrogen utilization, SKC1 for salt tolerance, and STV11 for resistance to rice stripe virus. Consequently, the restorer line GH5501 could serve as a valuable resource for the subsequent breeding of high-yielding, good-quality, and stress-tolerant hybrid rice varieties.

RNA-Seq analysis reveals the mechanism in response to cold stress of peach cv ‘Dingjiaba’

BACKGROUND: ‘Dingjiaba’ is an important Prunus persica cultivar (cv) mainly grown in the Hexi corridor in northwest China, which has an inherited strong cold tolerance. OBJECTIVE: To compare the transcriptome and physiology data of leaves of cvs ‘Dingjiaba’ (D) and ‘Kanoiwa’ (K) following cold treatment at different time periods, in order to gain new insights into the mechanisms of cold adaptation in ‘Dingjiaba’. MATERIALS AND METHODS: We analyzed the transcriptomic and physiological data of leaves of D and K cvs exposed to 0 h (D0/K0), 2 h (D2/K2), 6 h (D6/K6) and 12h (D12/K12) cold stress. RESULTS: Low temperature stress caused membrane damage and led to increased rate of electrolyte leakage and increased MDA content. Cold stress induced the accumulation of soluble sugars, soluble proteins and proline in leaves of both cvs, with a lower increase in K compared to D. Transcriptome analysis identified 4,631, 5,069, 5,662 and 3,886 differentially expressed genes (DEGs) between D0 and K0, D2 and K2, D6 and K6 and D12 and K12, respectively. The differentially expressed genes significantly enriched in metabolic pathways and biosynthesis of secondary metabolites. We further validated the reliability of sequencing data of the RNA-Seq with Real-Time Quantitative PCR, which suggested that the expression trend of the RNASeq were same as RT-PCR. CONCLUSIONS: These results provide novel insights into a series of molecular mechanisms underlying physiological metabolism and defense.

The chromosome-level genome assembly of Fraxinus americana provides insights into the evolution of Oleaceae plants

White ash (Fraxinus americana linn.) originates from the southeastern United States. It is a tall and fast-growing tree species with strong salt-alkali resistance and cold tolerance, making it an important reforestation species and widely planted worldwide. Here, we completed the chromosome-level reference genome assembly of F. americana based on Illumina, PacBio, and Hi-C reads, with a genome size of 878.98 Mb, an N50 of 3.27 Mb, and a heterozygosity rate of 0.3 %. Based on de novo prediction, transcriptome prediction, and homology-based protein prediction, we obtained 39,538 genes. Approximately 843.21 Mb of the assembly genome was composed of 37,928 annotated protein-coding genes, with a gene function annotation rate of 95.93 %. 99.94 % of the overlap clusters (877.44 Mb) were anchored to 23 chromosomes. Synteny analysis of F. americana and other Oleaceae plants showed that F. americana underwent frequent chromosome rearrangements. The amplification of the Ale transposons effectively promoted the genome size of F. americana. Compared with other Oleaceae plants, the Glutathione S-transferase (GST) gene family in the F. americana genome has undergone significant expansion, which may help F. americana cope with adverse natural environments. Furthermore, we found that key enzyme-coding gene families related to lignin biosynthesis were expanded and highly expressed in F. americana leaves. These key genes drive lignin synthesis and benefit F. americana in fast-growing, as well as resisting biotic and abiotic stress. Overall, the F. americana genome assembly provides insights into the evolution of Oleaceae plants and provides abundant resources for breeding and germplasm conservation of white ash.

基于生物量的玉米可视化模型构建

Maize is one of the characteristic species in Shanxi Province. It has strong drought and cold tolerance. The study of maize growth and development law through the construction of the model is helpful to accurately understand the growth characteristics of maize, improve the yield, and further provide an important theoretical basis for the realization of precision agriculture. In this paper, "Xianyu 335" maize was taken as the research object. The data of leaf length, leaf width, stem length, stem number and tassel length, as well as leaf, stem, tassel, ear, cob and root organ morphology and biomass of maize during the whole growth period were obtained by field experiment. The maize geometric form structure module was constructed. The dynamic simulation of maize growing process was realized by object-oriented programming in Visual Studio software platform. With the help of 3D OpenGL graphic library Nurbs (Non-Uniform Rational B-Splines) curve and surface simulation technology, the growth visualization of maize organs was realized based on the idea of curve and surface control point selection parameter modeling.

A comparative transcriptomic analysis reveals a coordinated mechanism activated in response to cold acclimation in common vetch (Vicia sativa L.)

Due to its strong abiotic stress tolerance, common vetch is widely cultivated as a green manure and forage crop in grass and crop rotation systems. The comprehensive molecular mechanisms activated in common vetch during cold adaptation remain unknown. We investigated physiological responses and transcriptome profiles of cold-sensitive (Lanjian No. 1) and cold-tolerant (Lanjian No. 3) cultivars during cold acclimation to explore the molecular mechanisms of cold acclimation. In total, 2681 and 2352 differentially expressed genes (DEGs) were identified in Lanjian No. 1 and Lanjian No. 3, respectively; 7532 DEGs were identified in both lines. DEGs involved in "plant hormone signal transduction" were significantly enriched during cold treatment, and 115 DEGs involved in cold-processed hormone signal transduction were identified. Common vetch increased the level of indoleacetic acid (IAA) by upregulating the transcriptional regulator Aux/IAA and downregulating GH3, endowing it with stronger cold tolerance. An auxin-related DEG was overexpressed in yeast and shown to possess a biological function conferring cold tolerance. This study identifies specific genes involved in Ca2+ signaling, redox regulation, circadian clock, plant hormones, and transcription factors whose transcriptional differentiation during cold acclimation may improve cold tolerance and contributes to the understanding of common and unique molecular mechanisms of cold acclimation in common vetch. The candidate genes identified here also provide valuable resources for further functional genomic and breeding studies.

Cadmium/lead tolerance of six Dianthus species and detoxification mechanism in Dianthus spiculifolius

Toxic heavy metal contaminants seriously affect plant growth and human health. Reducing the accumulation of toxic metals by phytoremediation is an effective way to solve this environmental problem. Dianthus spiculifolius Schur is an ornamental plant with strong cold and drought tolerance. Because of its fast growth, well-developed root system, and large accumulation of biomass, D. spiculifolius has potential applications as a heavy metal hyperaccumulator. Therefore, the aim of this study was evaluate the ability of D. spiculifolius and other Dianthus species to remediate heavy metals, with an ultimate goal to identify available genetic resources for toxic metal removal. The cadmium (Cd) and lead (Pb) tolerance and accumulation of six Dianthus species were analyzed comparatively in physiological and biochemical experiments. Compared with the other Dianthus species, D. spiculifolius showed higher tolerance to, and greater accumulation of, Cd and Pb. Second-generation transcriptome analysis indicated that glutathione transferase activity was increased and the glutathione metabolism pathway was enriched with genes encoding antioxidant enzymes (DsGST, DsGST3, DsGSTU10, DsGGCT2-1, and DsIDH-2) that were up-regulated under Cd/Pb treatment by RT-qPCR in D. spiculifolius. When expressed in yeast, DsGST, DsGST3, DsGSTU10 and DsIDH-2 enhanced Cd or Pb tolerance. These results indicate that D. spiculifolius has potential applications as a new ornamental hyperaccumulator plant, and that antioxidant enzymes might be involved in regulating Cd/Pb accumulation and detoxification. The findings of this study reveal some novel genetic resources that can be used to breed new plant varieties that tolerate and accumulate heavy metals.

Transcriptome responses to salt stress in roots and leaves of Lilium pumilum

Salt stress seriously affects the growth and development of plants. Most species of lilies are not salt tolerant, thus salt affecting their geographical application. As a wild flower, Lilium pumilum is an excellent breeding material because of its bright colors, strong salt tolerance and cold tolerance. There are few studies on the salt tolerance mechanism and salt tolerance gene mining of L. pumilum. In this study, the salt tolerance threshold of L. pumilum was determined to be approximately 150 mM and the abundant ion translocation occurs in roots and leaves at the concentration. RNA-seq was used to characterize the transcriptome differences between L. pumilum leaves and roots treated with 150 mM NaCl for 2 and 12 h. By de novo assembly, 47,763 and 76,871 unigenes were identified in L. pumilum leaves and roots, respectively. Differentially expressed genes in leaves were higher than those in roots at 2 h, whereas the opposite result was obtained at 12 h. GO analysis of DEGs showed that transcriptional regulation and redox processes were significantly enriched, and KEGG annotation indicated that L. pumilum roots and leaves responded to salt stress mainly through phytohormone signaling, MAPK signaling pathways, and starch and sucrose metabolism. These results reveal important salt stress-related genes and metabolic pathways in L. pumilum, providing valuable information for exploring the salt tolerance mechanism of L. pumilum, screening salt tolerance genes and breeding new salt-tolerant L. pumilum varieties.

The mechanism of abscisic acid regulation of wild Fragaria species in response to cold stress.

BackgroundAbiotic stresses have increasingly serious effects on the growth and yield of crops. Cold stress, in particular, is an increasing problem. In this study, Fragaria daltoniana and F. vesca were determined to be cold-resistant and cold-sensitive species, respectively. Integrated transcriptomics and metabolomics methods were used to analyze the regulatory mechanism of abscisic acid (ABA) in F. daltoniana and F. vesca in their response to low temperature stress.ResultsF. daltoniana and F. vesca increased their ABA content under low temperature stress by upregulating the expression of the ABA biosynthetic pathway gene NCED and downregulating the expression of the ABA degradative gene CYP707A. Both types of regulation increased the accumulation of glucose and fructose, resulting in a reduction of damage under low temperature stress. Twelve transcription factors were found to be involved in the ABA regulatory pathway. The strong cold tolerance of F. daltoniana could be owing to its higher levels of ABA that accumulated compared with those in F. vesca under low temperature stress. In addition, the gene ABF2, which is related to the transduction of glucose signaling, was significantly upregulated in the leaves of F. daltoniana, while it was downregulated in the leaves of F. vesca under low temperature stress. This could contribute to the higher levels of glucose signal transduction in F. daltoniana. Thus, this could explain the higher peroxidase activity and lower damage to cell membranes in the leaves of F. daltoniana compared with F. vesca under low temperature stress, which endows the former with stronger cold tolerance.ConclusionsUnder low temperature stress, the differences in the accumulation of ABA and the expression trends of ABF2 and ABF4 in different species of wild strawberries may be the primary reason for their differences in cold tolerance. Our results provide an important empirical reference and technical support for breeding resistant cultivated strawberry plants.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12864-022-08889-8.

Combination of Genomics, Transcriptomics Identifies Candidate Loci Related to Cold Tolerance in Dongxiang Wild Rice.

Rice, a cold-sensitive crop, is a staple food for more than 50% of the world’s population. Low temperature severely compromises the growth of rice and challenges China’s food safety. Dongxiang wild rice (DXWR) is the most northerly common wild rice in China and has strong cold tolerance, but the genetic basis of its cold tolerance is still unclear. Here, we report quantitative trait loci (QTLs) analysis for seedling cold tolerance (SCT) using a high-density single nucleotide polymorphism linkage map in the backcross recombinant inbred lines that were derived from a cross of DXWR, and an indica cultivar, GZX49. A total of 10 putative QTLs were identified for SCT under 4 °C cold treatment, each explaining 2.0–6.8% of the phenotypic variation in this population. Furthermore, transcriptome sequencing of DXWR seedlings before and after cold treatment was performed, and 898 and 3413 differentially expressed genes (DEGs) relative to 0 h in cold-tolerant for 4 h and 12 h were identified, respectively. Gene ontology and Kyoto encyclopedia of genes and genomes (KEGG) analysis were performed on these DEGs. Using transcriptome data and genetic linkage analysis, combined with qRT-PCR, sequence comparison, and bioinformatics, LOC_Os08g04840 was putatively identified as a candidate gene for the major effect locus qSCT8. These findings provided insights into the genetic basis of SCT for the improvement of cold stress potential in rice breeding programs.

Transcriptomic Insights Into Root Development and Overwintering Transcriptional Memory of Brassica rapa L. Grown in the Field.

As the only overwintering oil crop in the north area of China, living through winter is the primary feature of winter rapeseed. Roots are the only survival organ during prolonged cold exposure during winter to guarantee flowering in spring. However, little is known about its root development and overwintering memory mechanism. In this study, root collar tissues (including the shoot apical meristem) of three winter rapeseed varieties with different cold resistance, i.e., Longyou-7 (strong cold tolerance), Tianyou-4 (middle cold tolerance), and Lenox (cold-sensitive), were sampled in the pre-winter period (S1), overwintering periods (S2–S5), and re-greening stage (S6), and were used to identify the root development and overwintering memory mechanisms and seek candidate overwintering memory genes by measuring root collar diameter and RNA sequencing. The results showed that the S1–S2 stages were the significant developmental stages of the roots as root collar diameter increased slowly in the S3–S5 stages, and the roots developed fast in the strong cold resistance variety than in the weak cold resistance variety. Subsequently, the RNA-seq analysis revealed that a total of 37,905, 45,102, and 39,276 differentially expressed genes (DEGs), compared to the S1 stage, were identified in Longyou-7, Tianyou-4, and Lenox, respectively. The function enrichment analysis showed that most of the DEGs are significantly involved in phenylpropanoid biosynthesis, plant hormone signal transduction, MAPK signaling pathway, starch and sucrose metabolism, photosynthesis, amino sugar and nucleotide sugar metabolism, and spliceosome, ribosome, proteasome, and protein processing in endoplasmic reticulum pathways. Furthermore, the phenylpropanoid biosynthesis and plant hormone signal transduction pathways were related to the difference in root development of the three varieties, DEGs involved in photosynthesis and carbohydrate metabolism processes may participate in overwintering memory of Longyou-7 and Tianyou-4, and the spliceosome pathway may contribute to the super winter resistance of Longyou-7. The transcription factor enrichment analysis showed that the WRKY family made up the majority in different stages and may play an important regulatory role in root development and overwintering memory. These results provide a comprehensive insight into winter rapeseed's complex overwintering memory mechanisms. The identified candidate overwintering memory genes may also serve as important genetic resources for breeding to further improve the cold resistance of winter rapeseed.

Comparative Transcriptome Analysis Revealed the Freezing Tolerance Signaling Events in Winter Rapeseed (Brassica rapa L.).

Winter rapeseed (Brassica rapa L.) is an important oilseed crop in northwest China. Freezing stress severely limits its production and geographical distribution, and frequent extreme freezing events caused by climate change are increasing the chances of winter freeze-injury. However, the underlying mechanism of B. rapa response to freezing stress remains elusive. Here, B. rapa genome (v3.0) was used as a reference for the comparative transcriptomic analysis of Longyou 6 and Tianyou 2 (strong and weak cold tolerance, respectively) under different freezing stress. Before and after freezing stress, 5,982 and 11,630 unique differentially expressed genes (DEGs) between two cultivars were identified, respectively. After freezing stress, the GO terms in Tianyou 2 were mainly involved in “macromolecule biosynthetic process”, and those in Longyou 6 were involved in “response to stimulus” and “oxidoreductase activity”. Morphological and physiological results indicated that Longyou 6 retained a higher basal freezing resistance than Tinayou 2, and that cold acclimation could strengthen the basal freezing resistance. Freezing stress could activate the MAPK signal cascades, and the phosphorylation level of Longyou 6 showed a higher increase in response to freezing treatment than Tianyou 2. Based on our findings, it was speculated that the cell membrane of B. rapa perceives external signals under freezing stress, which are then transmitted to the nucleus through the cold-activated MAPK cascades and Ca2+-related protein kinase pathway, thus leading to activation of downstream target genes to enhance the freezing resistance of B. rapa.

Relationship between seed morphology, storage substance and chilling tolerance during germination of dominant maize hybrids in Northeast China

<p id="C3">Seed germination is the initial stage of crop morphology, which is determined by its own properties and environmental factors. Low temperature is one of the most important factors affecting seed germination. It is crucial to explore the relationship between seed properties and germination under low temperature environmental conditions for maize production in Northeast China. In the present study, 36 maize hybrids released in Northeast China were selected and the germination culture experiment was conducted under 6℃ (low temperature stress) and 15℃ (the control). The seedling vigor, seed germination rate, seed morphology and storage substances content were determined. The germination potential and germination rate of 36 maize hybrids were evaluated by the principal component analysis (PCA), the comprehensive evaluation value of cold tolerance (CL-value), and the membership function value (<italic>R</italic>-value). The relationship between the seed morphology (kernel length, kernel width, kernel thickness, kernel length/kernel width ratio, 100-kernel volume, and 100-kernel weight) and the seed storage substances (starch, protein, and fat) of 36 maize varieties were investigated. The results showed that the seedling vigor and germination rate of 36 maize hybrids were inhibited to some content, and the variation of relative seedling vigor cold injury rate and relative germination cold injury rate was the largest under low temperature stress. There was a significant correlation among the seven individual indicators that characterized cold tolerance. Principal component analysis could transform seven individual indicators into two independent comprehensive indicators. Among them, relative seedling vigor and relative germination rate had the largest positive contribution rate, which could be used as the key indicators for cold resistance evaluation at germination stage in maize. We classified 36 hybrids into four types of strong cold tolerance (19.4%), cold tolerance (30.6%), medium cold tolerance (33.3%), and cold sensitive (16.7%) by cluster analysis. Among them, Jidan 56, Kenji 267, Suiyu 23, Jidan 953, Kenji 268, Jidan 96, and Jidan 95 were strong cold-tolerant hybrids. The correlation analysis revealed that there was no significant correlation between seed morphology and cold tolerance. Starch content was significantly correlated with relative seedling vigor, relative germination rate, relative seedling vigor chilling injury rate, relative germination chilling injury rate, and relative germination time (<italic>r </italic>= 0.396^**, <italic>r </italic>= 0.404 ^**, <italic>r </italic>= -0.401 ^**, <italic>r </italic>= -0.391 ^**, and <italic>r </italic>= 0.362 ^**). There was a significant negative correlation between protein content and relative seedling vigor (<italic>r </italic>= -0.379^**). Regression analysis indicated that the types with high starch content had higher relative seedling vigor, relative germination rate, relative germination time, and lower relative seedling vigor, relative germination rate, and chilling injury rate. The regression model demonstrated that the seed starch content was 72.0%-74.0%, the relative seedling vigor was ≥70.0%, the relative germination rate was ≥80.5%, and the chilling injury rate of relative seedling vigor and relative germination rate was ≤50.0% under 6℃ stress. Under low temperature stress, the higher seed starch content was helpful to improve seed germination and reduce chilling injury. The varieties with starch content of 72.0%-74.0% were recommended to meet the requirements of seed germination in Northeast China.

Effects of root characteristics on panicle formation in japonica rice under low temperature water stress at the reproductive stage

Cold stress during the reproductive stage causes spikelet sterility and limits rice productivity in high-altitude and high-latitude regions. In higher plants, phytohormones regulate root and panicle development under environmental stress. Maintaining high root physiological activity during the reproductive stage may be a strategy for high yields in crops under abiotic stress. However, little is known about the root physiological activity and panicle size response mechanisms associated with rice cold tolerance at the reproductive stage. In this study, we investigated the effects of low root zone water temperature (Tw) during reproductive growth on root physiological characteristics and root phytohormones associated with panicle development in japonica rice from 2018 to 2019. The rice plants were subjected to 17 °C low Tw for 5, 10, and 15 days during reproductive growth. The results showed that, compared with the control, rice pollen grain development was hindered, and the percentage of fertile pollen decreased under low Tw; the number of surviving total panicle branches decreased significantly; the number of degraded branches increased significantly; the range of change increased gradually with the extension of low Tw stress time; and the impact of low Tw stress on the secondary branches and spikelets was greater than on the primary branches and spikelets. The abundance of zeatin (ZR) and auxin (IAA) in the roots, the root physiological activity, and the number of surviving spikelets and branches had a significant positive correlation in variety DN428. DN428 exhibited strong cold tolerance and possessed a high level of ZR and IAA in the roots, which allowed it to maintain root antioxidant enzyme activity, root vitality, and the root absorption surface area at a relatively stable level, resulting in the roots not accumulating large amounts of soluble protein, soluble sugar, malondialdehyde, and proline. This facilitated the accumulation and transfer of photosynthetic materials above the ground and provided a stable material foundation for spikelet and branch formation.

Seed production and yield components of Lespedeza davurica in response to N, P, and K fertilization and plant density

Lespedeza davurica Laxm is a valuable forage because of the strong cold and drought tolerance, and its high nutritional value. This crop production is limited by seed supply. The objective of this study was to investigate the effects of fertilization and plant density on seed yield. “JinNong 1” was drill-seeded in 2016 at 15 kg ha−1 at the Forage Research Station of Shanxi Agricultural University. The seedlings were manually thinned in May 2016 to two different densities, 6 and 12 plants m−2 in the main plots. Within each main plot, a factorial combination of N, P, and K fertilization levels were applied once a year from 2016 to 2018. The N levels were 0, 75, 125, and 175 kg ha−1. The P levels were 22 and 44 kg ha−1. The K levels were 62 and 124 kg ha−1. Maximum seed yield was achieved at the density of 12 plants m−2, 75 kg ha−1 of N, 22 kg ha−1 of P, and 124 kg ha−1 of K. The seed yields were 750 and 644 kg ha−1 during 2017 and 2018, respectively. High plant density showed a tradeoff with the number of primary and secondary branches, the number of raceme per branch, and 1000-seed weight. The number of pods per raceme and the number of flowers per raceme did not show a tradeoff at high density. Therefore, selecting for higher numbers of seed pods per raceme or fertile flowers may be a practical objective for breeders attempting to increase seed production.

Expression analysis of genes related to cold tolerance in Dendroctonus valens.

Pine beetles are well known in North America for their widespread devastation of pine forests. However, Dendroctonus valens LeConte is an important invasive forest pest in China also. Adults and larvae of this bark beetle mainly winter at the trunks and roots of Pinus tabuliformis and Pinus sylvestris; larvae, in particular, result in pine weakness or even death. Since the species was introduced from the United States to Shanxi in 1998, its distribution has spread northward. In 2017, it invaded a large area at the junction of Liaoning, Inner Mongolia and Hebei provinces, showing strong cold tolerance. To identify genes relevant to cold tolerance and the process of overwintering, we sequenced the transcriptomes of wintering and non-wintering adult and larval D. valens using the Illumina HiSeq platform. Differential expression analysis methods for other non-model organisms were used to compare transcript abundances in adults and larvae at two time periods, followed by the identification of functions and metabolic pathways related to genes associated with cold tolerance. We detected 4,387 and 6,091 differentially expressed genes (DEGs) between sampling dates in larvae and adults, respectively, and 1,140 common DEGs, including genes encoding protein phosphatase, very long-chain fatty acids protein, cytochrome P450, and putative leucine-rich repeat-containing proteins. In a Gene Ontology (GO) enrichment analysis, 1,140 genes were assigned to 44 terms, with significant enrichment for cellulase activity, hydrolase activity, and carbohydrate metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) classification and enrichment analyses showed that the lysosomal and purine metabolism pathways involved the most DEGs, the highly enriched terms included autophagy—animal, pentose and glucuronate interconversions and lysosomal processes. We identified 140 candidate genes associated with cold tolerance, including genes with established roles in this trait (e.g., genes encoding trehalose transporter, fructose-1,6-bisphosphatase, and trehalase). Our comparative transcriptome analysis of adult and larval D. valens in different conditions provides basic data for the discovery of key genes and molecular mechanisms underlying cold tolerance.

Identification of differentially expressed genes involved in amino acid and lipid accumulation of winter turnip rape (Brassica rapa L.) in response to cold stress.

Winter turnip rape (Brassica rapa L.) is an important overwintering oil crop that is widely planted in northwestern China. It considered to be a good genetic resource for cold-tolerant research because its roots can survive harsh winter conditions. Here, we performed comparative transcriptomics analysis of the roots of two winter turnip rape varieties, Longyou7 (L7, strong cold tolerance) and Tianyou2 (T2, low cold tolerance), under normal condition (CK) and cold stress (CT) condition. A total of 8,366 differentially expressed genes (DEGs) were detected between the two L7 root groups (L7CK_VS_L7CT), and 8,106 DEGs were detected for T2CK_VS_T2CT. Among the DEGs, two ω-3 fatty acid desaturase (FAD3), two delta-9 acyl-lipid desaturase 2 (ADS2), one diacylglycerol kinase (DGK), and one 3-ketoacyl-CoA synthase 2 (KCS2) were differentially expressed in the two varieties and identified to be related to fatty acid synthesis. Four glutamine synthetase cytosolic isozymes (GLN), serine acetyltransferase 1 (SAT1), and serine acetyltransferase 3 (SAT3) were down-regulated under cold stress, while S-adenosylmethionine decarboxylase proenzyme 1 (AMD1) had an up-regulation tendency in response to cold stress in the two samples. Moreover, the delta-1-pyrroline-5-carboxylate synthase (P5CS), δ-ornithine aminotransferase (δ-OAT), alanine-glyoxylate transaminase (AGXT), branched-chain-amino-acid transaminase (ilvE), alpha-aminoadipic semialdehyde synthase (AASS), Tyrosine aminotransferase (TAT) and arginine decarboxylase related to amino acid metabolism were identified in two cultivars variously expressed under cold stress. The above DEGs related to amino acid metabolism were suspected to the reason for amino acids content change. The RNA-seq data were validated by real-time quantitative RT-PCR of 19 randomly selected genes. The findings of our study provide the gene expression profile between two varieties of winter turnip rape, which lay the foundation for a deeper understanding of the highly complex regulatory mechanisms in plants during cold treatment.

Overwintering Larval Cold Tolerance of Sirex noctilio (Hymenoptera: Siricidae): Geographic Variation in Northeast China

Simple SummaryThe cold tolerance strategy of Sirex noctilio overwintering larvae was freeze-avoidance and their supercooling points adjusted seasonally to avoid icing damage. The cold hardiness between different populations varied on a spatiotemporal scale; specifically, the harsher the environment, the stronger the cold tolerance of overwintering Sirex noctilio larvae. A tunnel played a certain protective role but did not affect the low temperature parameters limiting the distribution of S. noctilio. We provide experimentally determined low temperature limiting parameters of Sirex noctilio and prove it has the opportunity to spread and colonize in other regions.Sirex noctilio (Hymenoptera: Siricidae) is an invasive pest that has spread and established in many regions worldwide. However, its cold tolerance strategy is still unclear. We measured the supercooling point (SCP) and the lower lethal temperature (LLT) of overwintering S. noctilio larvae during three overwintering periods in four geographically separated populations in China. In addition, using the statistical analysis of the local historical temperature data, we also conducted comprehensive studies of S. noctilio cold tolerance variations and strategies. We measured the SCP of all samples as S. noctilio could survive at its SCP during a short period of exposure (<48 h) and its cold tolerance strategy was freeze-avoidance. The average SCPs of the groups in different spatiotemporal scales were significantly related to average temperature variation with most individuals exhibiting stronger cold hardiness at low ambient temperatures. S. noctilio exhibited a strong cold tolerance and it has the ability to withstand lower temperatures in cold environments. The geographic population showed a positive tendency as the ambient temperature decreased, which would increase its chance of developing in cold regions.

Genotypic variation in cold tolerance of 18 Ethiopian rice cultivars in relation to their reproductive morphology

Abstract Male sterility induced by low temperatures during reproductive development is the major constraint on rice production in Ethiopia, which generally lies at high elevations. Because of a lack of phenotyping facilities, limited information is available on the cold tolerance of Ethiopian germplasm. We evaluated the genotypic variation in cold tolerance of 18 Ethiopian rice cultivars in two phenotyping facilities and characterized their cold tolerance in relation to their reproductive morphology in a 2-year trial in Japan. Genotypic variation in spikelet fertility was high after exposure to cold during reproductive development at both facilities, with fertility ranging from 0% to 90 %. ‘Andassa’ and ‘Tana’ had the highest fertility and ‘Fogera 2’ and ‘Getachew’ had the lowest. The two cold-tolerant germplasms had tolerance similar to that of the Japanese ‘Hitomebore’ (strong), whereas the susceptible germplasms had tolerance similar to that of the Japanese ‘Sasanishiki’ (weak). The variation in spikelet fertility was explained by both anther length and number of fertile pollen grains per anther under cold stress, and by anther length under unstressed control conditions in both years of the study; longer anther length and higher fertile pollen number leads to stronger cold tolerance. Our results suggest that anther length under unstressed conditions offers a pre-screening criterion for cold tolerance without requiring phenotyping facilities for screening.

Identification and characterization of a natural SNP variant in ALTERNATIVE OXIDASE gene associated with cold stress tolerance in watermelon

Alternative oxidase (AOX) is a mitochondrial enzyme encoded by a small nuclear gene family, which contains the two subfamilies, AOX1 and AOX2. In the present study on watermelon (Citrullus lanatus), only one ClAOX gene, belonging to AOX2 subfamily but having a similar gene structure to AtAOX1a, was found in the watermelon genome. The expression analysis suggested that ClAOX had the constitutive expression feature of AOX2 subfamily, but was cold inducible, which is normally considered an AOX1 subfamily feature. Moreover, one single nucleotide polymorphism (SNP) in ClAOX sequence, which led to the change from Lys (N) to Asn (K) in the 96th amino acids, was found among watermelon subspecies. Ectopic expression of two ClAOX alleles in the Arabidopsis aox1a knock-out mutant indicated that ClAOXK-expressing plants had stronger cold tolerance than aox1a mutant and ClAOXN-expressing plants. Our findings suggested watermelon genome contained a single ClAOX that possessed the expression features of both AOX1 and AOX2 subfamilies. A naturally existing SNP in ClAOX differentiated the cold tolerance of transgenic Arabidopsis plants, impling a possibility this gene might be a functional marker for stress-tolerance breeding.